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diff --git a/docs/threat_model/index.rst b/docs/threat_model/index.rst new file mode 100644 index 0000000..ad8b82a --- /dev/null +++ b/docs/threat_model/index.rst @@ -0,0 +1,22 @@ +Threat Model +============ + +Threat modeling is an important part of Secure Development Lifecycle (SDL) +that helps us identify potential threats and mitigations affecting a system. + +In the next sections, we first give a description of the target of evaluation +using a data flow diagram. Then we provide a list of threats we have identified +based on the data flow diagram and potential threat mitigations. + +.. toctree:: + :maxdepth: 1 + :caption: Contents + + threat_model + threat_model_spm + threat_model_el3_spm + threat_model_fvp_r + +-------------- + +*Copyright (c) 2021, Arm Limited and Contributors. All rights reserved.* diff --git a/docs/threat_model/threat_model.rst b/docs/threat_model/threat_model.rst new file mode 100644 index 0000000..38e5c87 --- /dev/null +++ b/docs/threat_model/threat_model.rst @@ -0,0 +1,896 @@ +Generic Threat Model +******************** + +************ +Introduction +************ + +This document provides a generic threat model for TF-A firmware. + +.. note:: + + This threat model doesn't consider Root and Realm worlds introduced by + :ref:`Realm Management Extension (RME)`. + +******************** +Target of Evaluation +******************** + +In this threat model, the target of evaluation is the Trusted +Firmware for A-class Processors (TF-A). This includes the boot ROM (BL1), +the trusted boot firmware (BL2) and the runtime EL3 firmware (BL31) as +shown on Figure 1. Everything else on Figure 1 is outside of the scope of +the evaluation. + +TF-A can be configured in various ways. In this threat model we consider +only the most basic configuration. To that end we make the following +assumptions: + +- All TF-A images are run from either ROM or on-chip trusted SRAM. This means + TF-A is not vulnerable to an attacker that can probe or tamper with off-chip + memory. + +- Trusted boot is enabled. This means an attacker can't boot arbitrary images + that are not approved by platform providers. + +- There is no Secure-EL2. We don't consider threats that may come with + Secure-EL2 software. + +- Measured boot is disabled. We do not consider the threats nor the mitigations + that may come with it. + +- No experimental features are enabled. We do not consider threats that may come + from them. + +Data Flow Diagram +================= + +Figure 1 shows a high-level data flow diagram for TF-A. The diagram +shows a model of the different components of a TF-A-based system and +their interactions with TF-A. A description of each diagram element +is given on Table 1. On the diagram, the red broken lines indicate +trust boundaries. Components outside of the broken lines +are considered untrusted by TF-A. + +.. uml:: ../resources/diagrams/plantuml/tfa_dfd.puml + :caption: Figure 1: TF-A Data Flow Diagram + +.. table:: Table 1: TF-A Data Flow Diagram Description + + +-----------------+--------------------------------------------------------+ + | Diagram Element | Description | + +=================+========================================================+ + | DF1 | | At boot time, images are loaded from non-volatile | + | | memory and verified by TF-A boot firmware. These | + | | images include TF-A BL2 and BL31 images, as well as | + | | other secure and non-secure images. | + +-----------------+--------------------------------------------------------+ + | DF2 | | TF-A log system framework outputs debug messages | + | | over a UART interface. | + +-----------------+--------------------------------------------------------+ + | DF3 | | Debug and trace IP on a platform can allow access | + | | to registers and memory of TF-A. | + +-----------------+--------------------------------------------------------+ + | DF4 | | Secure world software (e.g. trusted OS) interact | + | | with TF-A through SMC call interface and/or shared | + | | memory. | + +-----------------+--------------------------------------------------------+ + | DF5 | | Non-secure world software (e.g. rich OS) interact | + | | with TF-A through SMC call interface and/or shared | + | | memory. | + +-----------------+--------------------------------------------------------+ + | DF6 | | This path represents the interaction between TF-A and| + | | various hardware IPs such as TrustZone controller | + | | and GIC. At boot time TF-A configures/initializes the| + | | IPs and interacts with them at runtime through | + | | interrupts and registers. | + +-----------------+--------------------------------------------------------+ + + +*************** +Threat Analysis +*************** + +In this section we identify and provide assessment of potential threats to TF-A +firmware. The threats are identified for each diagram element on the +data flow diagram above. + +For each threat, we identify the *asset* that is under threat, the +*threat agent* and the *threat type*. Each threat is given a *risk rating* +that represents the impact and likelihood of that threat. We also discuss +potential mitigations. + +Assets +====== + +We have identified the following assets for TF-A: + +.. table:: Table 2: TF-A Assets + + +--------------------+---------------------------------------------------+ + | Asset | Description | + +====================+===================================================+ + | Sensitive Data | | These include sensitive data that an attacker | + | | must not be able to tamper with (e.g. the Root | + | | of Trust Public Key) or see (e.g. secure logs, | + | | debugging information such as crash reports). | + +--------------------+---------------------------------------------------+ + | Code Execution | | This represents the requirement that the | + | | platform should run only TF-A code approved by | + | | the platform provider. | + +--------------------+---------------------------------------------------+ + | Availability | | This represents the requirement that TF-A | + | | services should always be available for use. | + +--------------------+---------------------------------------------------+ + +Threat Agents +============= + +To understand the attack surface, it is important to identify potential +attackers, i.e. attack entry points. The following threat agents are +in scope of this threat model. + +.. table:: Table 3: Threat Agents + + +-------------------+-------------------------------------------------------+ + | Threat Agent | Description | + +===================+=======================================================+ + | NSCode | | Malicious or faulty code running in the Non-secure | + | | world, including NS-EL0 NS-EL1 and NS-EL2 levels | + +-------------------+-------------------------------------------------------+ + | SecCode | | Malicious or faulty code running in the secure | + | | world, including S-EL0 and S-EL1 levels | + +-------------------+-------------------------------------------------------+ + | AppDebug | | Physical attacker using debug signals to access | + | | TF-A resources | + +-------------------+-------------------------------------------------------+ + | PhysicalAccess | | Physical attacker having access to external device | + | | communication bus and to external flash | + | | communication bus using common hardware | + +-------------------+-------------------------------------------------------+ + +.. note:: + + In this threat model an advanced physical attacker that has the capability + to tamper with a hardware (e.g. "rewiring" a chip using a focused + ion beam (FIB) workstation or decapsulate the chip using chemicals) is + considered out-of-scope. + +Threat Types +============ + +In this threat model we categorize threats using the `STRIDE threat +analysis technique`_. In this technique a threat is categorized as one +or more of these types: ``Spoofing``, ``Tampering``, ``Repudiation``, +``Information disclosure``, ``Denial of service`` or +``Elevation of privilege``. + +Threat Risk Ratings +=================== + +For each threat identified, a risk rating that ranges +from *informational* to *critical* is given based on the likelihood of the +threat occuring if a mitigation is not in place, and the impact of the +threat (i.e. how severe the consequences could be). Table 4 explains each +rating in terms of score, impact and likelihood. + +.. table:: Table 4: Rating and score as applied to impact and likelihood + + +-----------------------+-------------------------+---------------------------+ + | **Rating (Score)** | **Impact** | **Likelihood** | + +=======================+=========================+===========================+ + | Critical (5) | | Extreme impact to | | Threat is almost | + | | entire organization | certain to be exploited.| + | | if exploited. | | + | | | | Knowledge of the threat | + | | | and how to exploit it | + | | | are in the public | + | | | domain. | + +-----------------------+-------------------------+---------------------------+ + | High (4) | | Major impact to entire| | Threat is relatively | + | | organization or single| easy to detect and | + | | line of business if | exploit by an attacker | + | | exploited | with little skill. | + +-----------------------+-------------------------+---------------------------+ + | Medium (3) | | Noticeable impact to | | A knowledgeable insider | + | | line of business if | or expert attacker could| + | | exploited. | exploit the threat | + | | | without much difficulty.| + +-----------------------+-------------------------+---------------------------+ + | Low (2) | | Minor damage if | | Exploiting the threat | + | | exploited or could | would require | + | | be used in conjunction| considerable expertise | + | | with other | and resources | + | | vulnerabilities to | | + | | perform a more serious| | + | | attack | | + +-----------------------+-------------------------+---------------------------+ + | Informational (1) | | Poor programming | | Threat is not likely | + | | practice or poor | to be exploited on its | + | | design decision that | own, but may be used to | + | | may not represent an | gain information for | + | | immediate risk on its | launching another | + | | own, but may have | attack | + | | security implications | | + | | if multiplied and/or | | + | | combined with other | | + | | threats. | | + +-----------------------+-------------------------+---------------------------+ + +Aggregate risk scores are assigned to identified threats; +specifically, the impact score multiplied by the likelihood score. +For example, a threat with high likelihood and low impact would have an +aggregate risk score of eight (8); that is, four (4) for high likelihood +multiplied by two (2) for low impact. The aggregate risk score determines +the finding's overall risk level, as shown in the following table. + +.. table:: Table 5: Overall risk levels and corresponding aggregate scores + + +---------------------+-----------------------------------+ + | Overall Risk Level | Aggregate Risk Score | + | | (Impact multiplied by Likelihood) | + +=====================+===================================+ + | Critical | 20–25 | + +---------------------+-----------------------------------+ + | High | 12–19 | + +---------------------+-----------------------------------+ + | Medium | 6–11 | + +---------------------+-----------------------------------+ + | Low | 2–5 | + +---------------------+-----------------------------------+ + | Informational | 1 | + +---------------------+-----------------------------------+ + +The likelihood and impact of a threat depends on the +target environment in which TF-A is running. For example, attacks +that require physical access are unlikely in server environments while +they are more common in Internet of Things(IoT) environments. +In this threat model we consider three target environments: +``Internet of Things(IoT)``, ``Mobile`` and ``Server``. + +Threat Assessment +================= + +The following threats were identified by applying STRIDE analysis on +each diagram element of the data flow diagram. + +For each threat, we strive to indicate whether the mitigations are currently +implemented or not. However, the answer to this question is not always straight +forward. Some mitigations are partially implemented in the generic code but also +rely on the platform code to implement some bits of it. This threat model aims +to be platform-independent and it is important to keep in mind that such threats +only get mitigated if the platform code properly fulfills its responsibilities. + +Also, some mitigations require enabling specific features, which must be +explicitly turned on via a build flag. + +These are highlighted in the ``Mitigations implemented?`` box. + ++------------------------+----------------------------------------------------+ +| ID | 01 | ++========================+====================================================+ +| Threat | | **An attacker can mangle firmware images to | +| | execute arbitrary code** | +| | | +| | | Some TF-A images are loaded from external | +| | storage. It is possible for an attacker to access| +| | the external flash memory and change its contents| +| | physically, through the Rich OS, or using the | +| | updating mechanism to modify the non-volatile | +| | images to execute arbitrary code. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF4, DF5 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | BL2, BL31 | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | Code Execution | ++------------------------+----------------------------------------------------+ +| Threat Agent | PhysicalAccess, NSCode, SecCode | ++------------------------+----------------------------------------------------+ +| Threat Type | Tampering, Elevation of Privilege | ++------------------------+------------------+-----------------+---------------+ +| Application | Server | IoT | Mobile | ++------------------------+------------------+-----------------+---------------+ +| Impact | Critical (5) | Critical (5) | Critical (5) | ++------------------------+------------------+-----------------+---------------+ +| Likelihood | Critical (5) | Critical (5) | Critical (5) | ++------------------------+------------------+-----------------+---------------+ +| Total Risk Rating | Critical (25) | Critical (25) | Critical (25) | ++------------------------+------------------+-----------------+---------------+ +| Mitigations | | 1) Implement the `Trusted Board Boot (TBB)`_ | +| | feature which prevents malicious firmware from | +| | running on the platform by authenticating all | +| | firmware images. | +| | | +| | | 2) Perform extra checks on unauthenticated data, | +| | such as FIP metadata, prior to use. | ++------------------------+----------------------------------------------------+ +| Mitigations | | 1) Yes, provided that the ``TRUSTED_BOARD_BOOT`` | +| implemented? | build option is set to 1. | +| | | +| | | 2) Yes. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 02 | ++========================+====================================================+ +| Threat | | **An attacker may attempt to boot outdated, | +| | potentially vulnerable firmware image** | +| | | +| | | When updating firmware, an attacker may attempt | +| | to rollback to an older version that has unfixed | +| | vulnerabilities. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF4, DF5 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | BL2, BL31 | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | Code Execution | ++------------------------+----------------------------------------------------+ +| Threat Agent | PhysicalAccess, NSCode, SecCode | ++------------------------+----------------------------------------------------+ +| Threat Type | Tampering | ++------------------------+------------------+-----------------+---------------+ +| Application | Server | IoT | Mobile | ++------------------------+------------------+-----------------+---------------+ +| Impact | Critical (5) | Critical (5) | Critical (5) | ++------------------------+------------------+-----------------+---------------+ +| Likelihood | Critical (5) | Critical (5) | Critical (5) | ++------------------------+------------------+-----------------+---------------+ +| Total Risk Rating | Critical (25) | Critical (25) | Critical (25) | ++------------------------+------------------+-----------------+---------------+ +| Mitigations | Implement anti-rollback protection using | +| | non-volatile counters (NV counters) as required | +| | by `TBBR-Client specification`_. | ++------------------------+----------------------------------------------------+ +| Mitigations | | Yes / Platform specific. | +| implemented? | | +| | | After a firmware image is validated, the image | +| | revision number taken from a certificate | +| | extension field is compared with the | +| | corresponding NV counter stored in hardware to | +| | make sure the new counter value is larger than | +| | the current counter value. | +| | | +| | | **Platforms must implement this protection using | +| | platform specific hardware NV counters.** | ++------------------------+----------------------------------------------------+ + ++------------------------+-------------------------------------------------------+ +| ID | 03 | ++========================+=======================================================+ +| Threat | | **An attacker can use Time-of-Check-Time-of-Use | +| | (TOCTOU) attack to bypass image authentication | +| | during the boot process** | +| | | +| | | Time-of-Check-Time-of-Use (TOCTOU) threats occur | +| | when the security check is produced before the time | +| | the resource is accessed. If an attacker is sitting | +| | in the middle of the off-chip images, they could | +| | change the binary containing executable code right | +| | after the integrity and authentication check has | +| | been performed. | ++------------------------+-------------------------------------------------------+ +| Diagram Elements | DF1 | ++------------------------+-------------------------------------------------------+ +| Affected TF-A | BL1, BL2 | +| Components | | ++------------------------+-------------------------------------------------------+ +| Assets | Code Execution, Sensitive Data | ++------------------------+-------------------------------------------------------+ +| Threat Agent | PhysicalAccess | ++------------------------+-------------------------------------------------------+ +| Threat Type | Elevation of Privilege | ++------------------------+---------------------+-----------------+---------------+ +| Application | Server | IoT | Mobile | ++------------------------+---------------------+-----------------+---------------+ +| Impact | N/A | Critical (5) | Critical (5) | ++------------------------+---------------------+-----------------+---------------+ +| Likelihood | N/A | Medium (3) | Medium (3) | ++------------------------+---------------------+-----------------+---------------+ +| Total Risk Rating | N/A | High (15) | High (15) | ++------------------------+---------------------+-----------------+---------------+ +| Mitigations | Copy image to on-chip memory before authenticating | +| | it. | ++------------------------+-------------------------------------------------------+ +| Mitigations | | Platform specific. | +| implemented? | | +| | | The list of images to load and their location is | +| | platform specific. Platforms are responsible for | +| | arranging images to be loaded in on-chip memory. | ++------------------------+-------------------------------------------------------+ + ++------------------------+-------------------------------------------------------+ +| ID | 04 | ++========================+=======================================================+ +| Threat | | **An attacker with physical access can execute | +| | arbitrary image by bypassing the signature | +| | verification stage using glitching techniques** | +| | | +| | | Glitching (Fault injection) attacks attempt to put | +| | a hardware into a undefined state by manipulating an| +| | environmental variable such as power supply. | +| | | +| | | TF-A relies on a chain of trust that starts with the| +| | ROTPK, which is the key stored inside the chip and | +| | the root of all validation processes. If an attacker| +| | can break this chain of trust, they could execute | +| | arbitrary code on the device. This could be | +| | achieved with physical access to the device by | +| | attacking the normal execution flow of the | +| | process using glitching techniques that target | +| | points where the image is validated against the | +| | signature. | ++------------------------+-------------------------------------------------------+ +| Diagram Elements | DF1 | ++------------------------+-------------------------------------------------------+ +| Affected TF-A | BL1, BL2 | +| Components | | ++------------------------+-------------------------------------------------------+ +| Assets | Code Execution | ++------------------------+-------------------------------------------------------+ +| Threat Agent | PhysicalAccess | ++------------------------+-------------------------------------------------------+ +| Threat Type | Tampering, Elevation of Privilege | ++------------------------+---------------------+-----------------+---------------+ +| Application | Server | IoT | Mobile | ++------------------------+---------------------+-----------------+---------------+ +| Impact | N/A | Critical (5) | Critical (5) | ++------------------------+---------------------+-----------------+---------------+ +| Likelihood | N/A | Medium (3) | Medium (3) | ++------------------------+---------------------+-----------------+---------------+ +| Total Risk Rating | N/A | High (15) | High (15) | ++------------------------+---------------------+-----------------+---------------+ +| Mitigations | Mechanisms to detect clock glitch and power | +| | variations. | ++------------------------+-------------------------------------------------------+ +| Mitigations | | No. | +| implemented? | | +| | | The most effective mitigation is adding glitching | +| | detection and mitigation circuit at the hardware | +| | level. | +| | | +| | | However, software techniques, such as adding | +| | redundant checks when performing conditional | +| | branches that are security sensitive, can be used | +| | to harden TF-A against such attacks. | +| | **At the moment TF-A doesn't implement such | +| | mitigations.** | ++------------------------+-------------------------------------------------------+ + ++------------------------+---------------------------------------------------+ +| ID | 05 | ++========================+===================================================+ +| Threat | | **Information leak via UART logs** | +| | | +| | | During the development stages of software it is | +| | common to print all sorts of information on the | +| | console, including sensitive or confidential | +| | information such as crash reports with detailed | +| | information of the CPU state, current registers | +| | values, privilege level or stack dumps. | +| | | +| | | This information is useful when debugging | +| | problems before releasing the production | +| | version but it could be used by an attacker | +| | to develop a working exploit if left enabled in | +| | the production version. | +| | | +| | | This happens when directly logging sensitive | +| | information and more subtly when logging | +| | side-channel information that can be used by an | +| | attacker to learn about sensitive information. | ++------------------------+---------------------------------------------------+ +| Diagram Elements | DF2 | ++------------------------+---------------------------------------------------+ +| Affected TF-A | BL1, BL2, BL31 | +| Components | | ++------------------------+---------------------------------------------------+ +| Assets | Sensitive Data | ++------------------------+---------------------------------------------------+ +| Threat Agent | AppDebug | ++------------------------+---------------------------------------------------+ +| Threat Type | Information Disclosure | ++------------------------+------------------+----------------+---------------+ +| Application | Server | IoT | Mobile | ++------------------------+------------------+----------------+---------------+ +| Impact | N/A | Low (2) | Low (2) | ++------------------------+------------------+----------------+---------------+ +| Likelihood | N/A | High (4) | High (4) | ++------------------------+------------------+----------------+---------------+ +| Total Risk Rating | N/A | Medium (8) | Medium (8) | ++------------------------+------------------+----------------+---------------+ +| Mitigations | | Remove sensitive information logging in | +| | production releases. | +| | | +| | | Do not conditionally log information depending | +| | on potentially sensitive data. | +| | | +| | | Do not log high precision timing information. | ++------------------------+---------------------------------------------------+ +| Mitigations | | Yes / Platform Specific. | +| implemented? | Requires the right build options to be used. | +| | | +| | | Crash reporting is only enabled for debug | +| | builds by default, see ``CRASH_REPORTING`` | +| | build option. | +| | | +| | | The log level can be tuned at build time, from | +| | very verbose to no output at all. See | +| | ``LOG_LEVEL`` build option. By default, release | +| | builds are a lot less verbose than debug ones | +| | but still produce some output. | +| | | +| | | Messages produced by the platform code should | +| | use the appropriate level of verbosity so as | +| | not to leak sensitive information in production | +| | builds. | ++------------------------+---------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 06 | ++========================+====================================================+ +| Threat | | **An attacker can read sensitive data and | +| | execute arbitrary code through the external | +| | debug and trace interface** | +| | | +| | | Arm processors include hardware-assisted debug | +| | and trace features that can be controlled without| +| | the need for software operating on the platform. | +| | If left enabled without authentication, this | +| | feature can be used by an attacker to inspect and| +| | modify TF-A registers and memory allowing the | +| | attacker to read sensitive data and execute | +| | arbitrary code. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | BL1, BL2, BL31 | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | Code Execution, Sensitive Data | ++------------------------+----------------------------------------------------+ +| Threat Agent | AppDebug | ++------------------------+----------------------------------------------------+ +| Threat Type | Tampering, Information Disclosure, | +| | Elevation of privilege | ++------------------------+------------------+---------------+-----------------+ +| Application | Server | IoT | Mobile | ++------------------------+------------------+---------------+-----------------+ +| Impact | N/A | High (4) | High (4) | ++------------------------+------------------+---------------+-----------------+ +| Likelihood | N/A | Critical (5) | Critical (5) | ++------------------------+------------------+---------------+-----------------+ +| Total Risk Rating | N/A | Critical (20) | Critical (20) | ++------------------------+------------------+---------------+-----------------+ +| Mitigations | Disable the debug and trace capability for | +| | production releases or enable proper debug | +| | authentication as recommended by [`DEN0034`_]. | ++------------------------+----------------------------------------------------+ +| Mitigations | | Platform specific. | +| implemented? | | +| | | Configuration of debug and trace capabilities is | +| | entirely platform specific. | ++------------------------+----------------------------------------------------+ + ++------------------------+------------------------------------------------------+ +| ID | 07 | ++========================+======================================================+ +| Threat | | **An attacker can perform a denial-of-service | +| | attack by using a broken SMC call that causes the | +| | system to reboot or enter into unknown state.** | +| | | +| | | Secure and non-secure clients access TF-A services | +| | through SMC calls. Malicious code can attempt to | +| | place the TF-A runtime into an inconsistent state | +| | by calling unimplemented SMC call or by passing | +| | invalid arguments. | ++------------------------+------------------------------------------------------+ +| Diagram Elements | DF4, DF5 | ++------------------------+------------------------------------------------------+ +| Affected TF-A | BL31 | +| Components | | ++------------------------+------------------------------------------------------+ +| Assets | Availability | ++------------------------+------------------------------------------------------+ +| Threat Agent | NSCode, SecCode | ++------------------------+------------------------------------------------------+ +| Threat Type | Denial of Service | ++------------------------+-------------------+----------------+-----------------+ +| Application | Server | IoT | Mobile | ++------------------------+-------------------+----------------+-----------------+ +| Impact | Medium (3) | Medium (3) | Medium (3) | ++------------------------+-------------------+----------------+-----------------+ +| Likelihood | High (4) | High (4) | High (4) | ++------------------------+-------------------+----------------+-----------------+ +| Total Risk Rating | High (12) | High (12) | High (12) | ++------------------------+-------------------+----------------+-----------------+ +| Mitigations | Validate SMC function ids and arguments before using | +| | them. | ++------------------------+------------------------------------------------------+ +| Mitigations | | Yes / Platform specific. | +| implemented? | | +| | | For standard services, all input is validated. | +| | | +| | | Platforms that implement SiP services must also | +| | validate SMC call arguments. | ++------------------------+------------------------------------------------------+ + ++------------------------+------------------------------------------------------+ +| ID | 08 | ++========================+======================================================+ +| Threat | | **Memory corruption due to memory overflows and | +| | lack of boundary checking when accessing resources | +| | could allow an attacker to execute arbitrary code, | +| | modify some state variable to change the normal | +| | flow of the program, or leak sensitive | +| | information** | +| | | +| | | Like in other software, TF-A has multiple points | +| | where memory corruption security errors can arise. | +| | | +| | | Some of the errors include integer overflow, | +| | buffer overflow, incorrect array boundary checks, | +| | and incorrect error management. | +| | Improper use of asserts instead of proper input | +| | validations might also result in these kinds of | +| | errors in release builds. | ++------------------------+------------------------------------------------------+ +| Diagram Elements | DF4, DF5 | ++------------------------+------------------------------------------------------+ +| Affected TF-A | BL1, BL2, BL31 | +| Components | | ++------------------------+------------------------------------------------------+ +| Assets | Code Execution, Sensitive Data | ++------------------------+------------------------------------------------------+ +| Threat Agent | NSCode, SecCode | ++------------------------+------------------------------------------------------+ +| Threat Type | Tampering, Information Disclosure, | +| | Elevation of Privilege | ++------------------------+-------------------+-----------------+----------------+ +| Application | Server | IoT | Mobile | ++------------------------+-------------------+-----------------+----------------+ +| Impact | Critical (5) | Critical (5) | Critical (5) | ++------------------------+-------------------+-----------------+----------------+ +| Likelihood | Medium (3 | Medium (3) | Medium (3) | ++------------------------+-------------------+-----------------+----------------+ +| Total Risk Rating | High (15) | High (15) | High (15) | ++------------------------+-------------------+-----------------+----------------+ +| Mitigations | | 1) Use proper input validation. | +| | | +| | | 2) Code reviews, testing. | ++------------------------+------------------------------------------------------+ +| Mitigations | | 1) Yes. | +| implemented? | Data received from normal world, such as addresses | +| | and sizes identifying memory regions, are | +| | sanitized before being used. These security checks | +| | make sure that the normal world software does not | +| | access memory beyond its limit. | +| | | +| | | By default *asserts* are only used to check for | +| | programming errors in debug builds. Other types of | +| | errors are handled through condition checks that | +| | remain enabled in release builds. See | +| | `TF-A error handling policy`_. TF-A provides an | +| | option to use *asserts* in release builds, however | +| | we recommend using proper runtime checks instead | +| | of relying on asserts in release builds. | +| | | +| | | 2) Yes. | +| | TF-A uses a combination of manual code reviews | +| | and automated program analysis and testing to | +| | detect and fix memory corruption bugs. All TF-A | +| | code including platform code go through manual | +| | code reviews. Additionally, static code analysis | +| | is performed using Coverity Scan on all TF-A code. | +| | The code is also tested with | +| | `Trusted Firmware-A Tests`_ on Juno and FVP | +| | platforms. | ++------------------------+------------------------------------------------------+ + ++------------------------+------------------------------------------------------+ +| ID | 09 | ++========================+======================================================+ +| Threat | | **Improperly handled SMC calls can leak register | +| | contents** | +| | | +| | | When switching between worlds, TF-A register state | +| | can leak to software in different security | +| | contexts. | ++------------------------+------------------------------------------------------+ +| Diagram Elements | DF4, DF5 | ++------------------------+------------------------------------------------------+ +| Affected TF-A | BL31 | +| Components | | ++------------------------+------------------------------------------------------+ +| Assets | Sensitive Data | ++------------------------+------------------------------------------------------+ +| Threat Agent | NSCode, SecCode | ++------------------------+------------------------------------------------------+ +| Threat Type | Information Disclosure | ++------------------------+-------------------+----------------+-----------------+ +| Application | Server | IoT | Mobile | ++------------------------+-------------------+----------------+-----------------+ +| Impact | Medium (3) | Medium (3) | Medium (3) | ++------------------------+-------------------+----------------+-----------------+ +| Likelihood | High (4) | High (4) | High (4) | ++------------------------+-------------------+----------------+-----------------+ +| Total Risk Rating | High (12) | High (12) | High (12) | ++------------------------+-------------------+----------------+-----------------+ +| Mitigations | Save and restore registers when switching contexts. | ++------------------------+------------------------------------------------------+ +| Mitigations | | Yes. | +| implemented? | | +| | | This is the default behaviour in TF-A. | +| | Build options are also provided to save/restore | +| | additional registers such as floating-point | +| | registers. These should be enabled if required. | ++------------------------+------------------------------------------------------+ + ++------------------------+-----------------------------------------------------+ +| ID | 10 | ++========================+=====================================================+ +| Threat | | **SMC calls can leak sensitive information from | +| | TF-A memory via microarchitectural side channels**| +| | | +| | | Microarchitectural side-channel attacks such as | +| | `Spectre`_ can be used to leak data across | +| | security boundaries. An attacker might attempt to | +| | use this kind of attack to leak sensitive | +| | data from TF-A memory. | ++------------------------+-----------------------------------------------------+ +| Diagram Elements | DF4, DF5 | ++------------------------+-----------------------------------------------------+ +| Affected TF-A | BL31 | +| Components | | ++------------------------+-----------------------------------------------------+ +| Assets | Sensitive Data | ++------------------------+-----------------------------------------------------+ +| Threat Agent | SecCode, NSCode | ++------------------------+-----------------------------------------------------+ +| Threat Type | Information Disclosure | ++------------------------+-------------------+----------------+----------------+ +| Application | Server | IoT | Mobile | ++------------------------+-------------------+----------------+----------------+ +| Impact | Medium (3) | Medium (3) | Medium (3) | ++------------------------+-------------------+----------------+----------------+ +| Likelihood | Medium (3) | Medium (3) | Medium (3) | ++------------------------+-------------------+----------------+----------------+ +| Total Risk Rating | Medium (9) | Medium (9) | Medium (9) | ++------------------------+-------------------+----------------+----------------+ +| Mitigations | Enable appropriate side-channel protections. | ++------------------------+-----------------------------------------------------+ +| Mitigations | | Yes / Platform specific. | +| implemented? | | +| | | TF-A implements software mitigations for Spectre | +| | type attacks as recommended by `Cache Speculation | +| | Side-channels`_ for the generic code. | +| | | +| | | SiPs should implement similar mitigations for | +| | code that is deemed to be vulnerable to such | +| | attacks. | ++------------------------+-----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 11 | ++========================+====================================================+ +| Threat | | **Misconfiguration of the Memory Management Unit | +| | (MMU) may allow a normal world software to | +| | access sensitive data or execute arbitrary | +| | code** | +| | | +| | | A misconfiguration of the MMU could | +| | lead to an open door for software running in the | +| | normal world to access sensitive data or even | +| | execute code if the proper security mechanisms | +| | are not in place. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF5, DF6 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | BL1, BL2, BL31 | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | Sensitive Data, Code execution | ++------------------------+----------------------------------------------------+ +| Threat Agent | NSCode | ++------------------------+----------------------------------------------------+ +| Threat Type | Information Disclosure, Elevation of Privilege | ++------------------------+-----------------+-----------------+----------------+ +| Application | Server | IoT | Mobile | ++------------------------+-----------------+-----------------+----------------+ +| Impact | Critical (5) | Critical (5) | Critical (5) | ++------------------------+-----------------+-----------------+----------------+ +| Likelihood | High (4) | High (4) | High (4) | ++------------------------+-----------------+-----------------+----------------+ +| Total Risk Rating | Critical (20) | Critical (20) | Critical (20) | ++------------------------+-----------------+-----------------+----------------+ +| Mitigations | When configuring access permissions, the | +| | principle of least privilege ought to be | +| | enforced. This means we should not grant more | +| | privileges than strictly needed, e.g. code | +| | should be read-only executable, read-only data | +| | should be read-only execute-never, and so on. | ++------------------------+----------------------------------------------------+ +| Mitigations | | Platform specific. | +| implemented? | | +| | | MMU configuration is platform specific, | +| | therefore platforms need to make sure that the | +| | correct attributes are assigned to memory | +| | regions. | +| | | +| | | TF-A provides a library which abstracts the | +| | low-level details of MMU configuration. It | +| | provides well-defined and tested APIs. | +| | Platforms are encouraged to use it to limit the | +| | risk of misconfiguration. | ++------------------------+----------------------------------------------------+ + ++------------------------+-----------------------------------------------------+ +| ID | 12 | ++========================+=====================================================+ +| Threat | | **Incorrect configuration of Performance Monitor | +| | Unit (PMU) counters can allow an attacker to | +| | mount side-channel attacks using information | +| | exposed by the counters** | +| | | +| | | Non-secure software can configure PMU registers | +| | to count events at any exception level and in | +| | both Secure and Non-secure states. This allows | +| | a Non-secure software (or a lower-level Secure | +| | software) to potentially carry out | +| | side-channel timing attacks against TF-A. | ++------------------------+-----------------------------------------------------+ +| Diagram Elements | DF5, DF6 | ++------------------------+-----------------------------------------------------+ +| Affected TF-A | BL31 | +| Components | | ++------------------------+-----------------------------------------------------+ +| Assets | Sensitive Data | ++------------------------+-----------------------------------------------------+ +| Threat Agent | NSCode | ++------------------------+-----------------------------------------------------+ +| Threat Type | Information Disclosure | ++------------------------+-------------------+----------------+----------------+ +| Impact | Medium (3) | Medium (3) | Medium (3) | ++------------------------+-------------------+----------------+----------------+ +| Likelihood | Low (2) | Low (2) | Low (2) | ++------------------------+-------------------+----------------+----------------+ +| Total Risk Rating | Medium (6) | Medium (6) | Medium (6) | ++------------------------+-------------------+----------------+----------------+ +| Mitigations | Follow mitigation strategies as described in | +| | `Secure Development Guidelines`_. | ++------------------------+-----------------------------------------------------+ +| Mitigations | | Yes / platform specific. | +| implemented? | | +| | | General events and cycle counting in the Secure | +| | world is prohibited by default when applicable. | +| | | +| | | However, on some implementations (e.g. PMUv3) | +| | Secure world event counting depends on external | +| | debug interface signals, i.e. Secure world event | +| | counting is enabled if external debug is enabled. | +| | | +| | | Configuration of debug signals is platform | +| | specific, therefore platforms need to make sure | +| | that external debug is disabled in production or | +| | proper debug authentication is in place. This | +| | should be the case if threat #06 is properly | +| | mitigated. | ++------------------------+-----------------------------------------------------+ + +-------------- + +*Copyright (c) 2021-2022, Arm Limited. All rights reserved.* + + +.. _STRIDE threat analysis technique: https://docs.microsoft.com/en-us/azure/security/develop/threat-modeling-tool-threats#stride-model +.. _DEN0034: https://developer.arm.com/documentation/den0034/latest +.. _Cache Speculation Side-channels: https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability +.. _Spectre: https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability +.. _TBBR-Client specification: https://developer.arm.com/documentation/den0006/d/ +.. _Trusted Board Boot (TBB): https://trustedfirmware-a.readthedocs.io/en/latest/design/trusted-board-boot.html +.. _TF-A error handling policy: https://trustedfirmware-a.readthedocs.io/en/latest/process/coding-guidelines.html#error-handling-and-robustness +.. _Secure Development Guidelines: https://trustedfirmware-a.readthedocs.io/en/latest/process/security-hardening.html#secure-development-guidelines +.. _Trusted Firmware-A Tests: https://git.trustedfirmware.org/TF-A/tf-a-tests.git/about/ diff --git a/docs/threat_model/threat_model_el3_spm.rst b/docs/threat_model/threat_model_el3_spm.rst new file mode 100644 index 0000000..c3af7a2 --- /dev/null +++ b/docs/threat_model/threat_model_el3_spm.rst @@ -0,0 +1,650 @@ +EL3 SPMC Threat Model +********************* + +************ +Introduction +************ +This document provides a threat model for the TF-A `EL3 Secure Partition Manager`_ +(EL3 SPM) implementation. The EL3 SPM implementation is based on the +`Arm Firmware Framework for Arm A-profile`_ specification. + +******************** +Target of Evaluation +******************** +In this threat model, the target of evaluation is the ``Secure Partition Manager Core`` +component (SPMC) within the EL3 firmware. +The monitor and SPMD at EL3 are covered by the `Generic TF-A threat model`_. + +The scope for this threat model is: + +- The TF-A implementation for the EL3 SPMC +- The implementation complies with the FF-A v1.1 specification. +- Secure partition is statically provisioned at boot time. +- Focus on the run-time part of the life-cycle (no specific emphasis on boot + time, factory firmware provisioning, firmware udpate etc.) +- Not covering advanced or invasive physical attacks such as decapsulation, + FIB etc. + +Data Flow Diagram +================= +Figure 1 shows a high-level data flow diagram for the SPM split into an SPMD +and SPMC component at EL3. The SPMD mostly acts as a relayer/pass-through between +the normal world and the secure world. It is assumed to expose small attack surface. + +A description of each diagram element is given in Table 1. In the diagram, the +red broken lines indicate trust boundaries. + +Components outside of the broken lines are considered untrusted. + +.. uml:: ../resources/diagrams/plantuml/el3_spm_dfd.puml + :caption: Figure 1: EL3 SPMC Data Flow Diagram + +.. table:: Table 1: EL3 SPMC Data Flow Diagram Description + + +---------------------+--------------------------------------------------------+ + | Diagram Element | Description | + +=====================+========================================================+ + | DF1 | SP to SPMC communication. FF-A function invocation or | + | | implementation-defined Hypervisor call. | + | | | + | | Note:- To communicate with LSP, SP1 performs a direct | + | | message request to SPMC targeting LSP as destination. | + +---------------------+--------------------------------------------------------+ + | DF2 | SPMC to SPMD communication. | + +---------------------+--------------------------------------------------------+ + | DF3 | SPMD to NS forwarding. | + +---------------------+--------------------------------------------------------+ + | DF4 | SPMC to LSP communication. | + | | NWd to LSP communication happens through SPMC. | + | | LSP can send direct response SP1 or NWd through SPMC. | + +---------------------+--------------------------------------------------------+ + | DF5 | HW control. | + +---------------------+--------------------------------------------------------+ + | DF6 | Bootloader image loading. | + +---------------------+--------------------------------------------------------+ + | DF7 | External memory access. | + +---------------------+--------------------------------------------------------+ + + +*************** +Threat Analysis +*************** + +This threat model follows a similar methodology to the `Generic TF-A threat model`_. +The following sections define: + +- Trust boundaries +- Assets +- Theat agents +- Threat types + +Trust boundaries +================ + +- Normal world is untrusted. +- Secure world and normal world are separate trust boundaries. +- EL3 monitor, SPMD and SPMC are trusted. +- Bootloaders (in particular BL1/BL2 if using TF-A) and run-time BL31 are + implicitely trusted by the usage of trusted boot. +- EL3 monitor, SPMD, SPMC do not trust SPs. + +Assets +====== + +The following assets are identified: + +- SPMC state. +- SP state. +- Information exchange between endpoints (partition messages). +- SPMC secrets (e.g. pointer authentication key when enabled) +- SP secrets (e.g. application keys). +- Scheduling cycles. +- Shared memory. + +Threat Agents +============= + +The following threat agents are identified: + +- Non-secure endpoint (referred NS-Endpoint later): normal world client at + NS-EL2 (Hypervisor) or NS-EL1 (VM or OS kernel). +- Secure endpoint (referred as S-Endpoint later): typically a secure partition. +- Hardware attacks (non-invasive) requiring a physical access to the device, + such as bus probing or DRAM stress. + +Threat types +============ + +The following threat categories as exposed in the `Generic TF-A threat model`_ +are re-used: + +- Spoofing +- Tampering +- Repudiation +- Information disclosure +- Denial of service +- Elevation of privileges + +Similarly this threat model re-uses the same threat risk ratings. The risk +analysis is evaluated based on the environment being ``Server`` or ``Mobile``. +IOT is not evaluated as the EL3 SPMC is primarily meant for use in Client. + +Threat Assessment +================= + +The following threats are identified by applying STRIDE analysis on each diagram +element of the data flow diagram. + ++------------------------+----------------------------------------------------+ +| ID | 01 | ++========================+====================================================+ +| Threat | **An endpoint impersonates the sender | +| | FF-A ID in a direct request/response invocation.** | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMD, SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SP state | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Spoofing | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------++------------------------+ +| Impact | Critical(5) | Critical(5) | ++------------------------+--------------------------++------------------------+ +| Likelihood | Critical(5) | Critical(5) | ++------------------------+--------------------------++------------------------+ +| Total Risk Rating | Critical(25) | Critical(25) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | SPMC must be able to correctly identify an | +| | endpoint and enforce checks to disallow spoofing. | ++------------------------+----------------------------------------------------+ +| Mitigations | Yes. | +| implemented? | The SPMC enforces checks in the direct message | +| | request/response interfaces such an endpoint cannot| +| | spoof the origin and destination worlds (e.g. a NWd| +| | originated message directed to the SWd cannot use a| +| | SWd ID as the sender ID). | +| | Also enforces check for direct response being sent | +| | only to originator of request. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 02 | ++========================+====================================================+ +| Threat | **An endpoint impersonates the receiver | +| | FF-A ID in a direct request/response invocation.** | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMD, SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SP state | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Spoofing, Denial of Service | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------++------------------------+ +| Impact | Critical(5) | Critical(5) | ++------------------------+--------------------------++------------------------+ +| Likelihood | Critical(5) | Critical(5) | ++------------------------+--------------------------++------------------------+ +| Total Risk Rating | Critical(25) | Critical(25) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | Validate if endpoind has permission to send | +| | request to other endpoint by implementation | +| | defined means. | ++------------------------+----------------------------------------------------+ +| Mitigations | Platform specific. | +| implemented? | | +| | The guidance below is left for a system integrator | +| | to implement as necessary. | +| | | +| | Additionally a software component residing in the | +| | SPMC can be added for the purpose of direct | +| | request/response filtering. | +| | | +| | It can be configured with the list of known IDs | +| | and about which interaction can occur between one | +| | and another endpoint (e.g. which NWd endpoint ID | +| | sends a direct request to which SWd endpoint ID). | +| | | +| | This component checks the sender/receiver fields | +| | for a legitimate communication between endpoints. | +| | | +| | A similar component can exist in the OS kernel | +| | driver, or Hypervisor although it remains untrusted| +| | by the SPMD/SPMC. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 03 | ++========================+====================================================+ +| Threat | **Tampering with memory shared between an endpoint | +| | and the SPMC.** | +| | | +| | A malicious endpoint may attempt tampering with its| +| | RX/TX buffer contents while the SPMC is processing | +| | it (TOCTOU). | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF3, DF7 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | Shared memory, Information exchange | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Tampering | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | High (4) | High (4) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | High (4) | High (4) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | High (16) | High (16) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | Validate all inputs, copy before use. | ++------------------------+----------------------------------------------------+ +| Mitigations | Yes. In context of FF-A v1.1 this is the case of | +| implemented? | sharing the RX/TX buffer pair and usage in the | +| | PARTITION_INFO_GET or memory sharing primitives. | +| | | +| | The SPMC copies the contents of the TX buffer | +| | to an internal temporary buffer before processing | +| | its contents. The SPMC implements hardened input | +| | validation on data transmitted through the TX | +| | buffer by an untrusted endpoint. | +| | | +| | The TF-A SPMC enforces | +| | checks on data transmitted through RX/TX buffers. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 04 | ++========================+====================================================+ +| Threat | **An endpoint may tamper with its own state or the | +| | state of another endpoint.** | +| | | +| | A malicious endpoint may attempt violating: | +| | | +| | - its own or another SP state by using an unusual | +| | combination (or out-of-order) FF-A function | +| | invocations. | +| | This can also be an endpoint emitting FF-A | +| | function invocations to another endpoint while | +| | the latter in not in a state to receive it (e.g. | +| | SP sends a direct request to the normal world | +| | early while the normal world is not booted yet). | +| | - the SPMC state itself by employing unexpected | +| | transitions in FF-A memory sharing, direct | +| | requests and responses, or handling of interrupts| +| | This can be led by random stimuli injection or | +| | fuzzing. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMD, SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SP state, SPMC state | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Tampering | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | High (4) | High (4) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | High (12) | High (12) | ++------------------------+------------------+-----------------+---------------+ +| Mitigations | Follow guidelines in FF-A v1.1 specification on | +| | state transitions (run-time model). | ++------------------------+----------------------------------------------------+ +| Mitigations | Yes. The TF-A SPMC is hardened to follow this | +| implemented? | guidance. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 05 | ++========================+====================================================+ +| Threat | **Replay fragments of past communication between | +| | endpoints.** | +| | | +| | A malicious endpoint may replay a message exchange | +| | that occurred between two legitimate endpoints as | +| | a matter of triggering a malfunction or extracting | +| | secrets from the receiving endpoint. In particular | +| | the memory sharing operation with fragmented | +| | messages between an endpoint and the SPMC may be | +| | replayed by a malicious agent as a matter of | +| | getting access or gaining permissions to a memory | +| | region which does not belong to this agent. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF2, DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | Information exchange | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Repudiation | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | High (4) | High (4) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | High (12) | High (12) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | Strict input validation and state tracking. | ++------------------------+----------------------------------------------------+ +| Mitigations | Platform specific. | +| implemented? | | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 06 | ++========================+====================================================+ +| Threat | **A malicious endpoint may attempt to extract data | +| | or state information by the use of invalid or | +| | incorrect input arguments.** | +| | | +| | Lack of input parameter validation or side effects | +| | of maliciously forged input parameters might affect| +| | the SPMC. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMD, SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SP secrets, SPMC secrets, SP state, SPMC state | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Information discolure | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | High (4) | High (4) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | High (12) | High (12) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | SPMC must be prepared to receive incorrect input | +| | data from secure partitions and reject them | +| | appropriately. | +| | The use of software (canaries) or hardware | +| | hardening techniques (XN, WXN, pointer | +| | authentication) helps detecting and stopping | +| | an exploitation early. | ++------------------------+----------------------------------------------------+ +| Mitigations | Yes. The TF-A SPMC mitigates this threat by | +| implemented? | implementing stack protector, pointer | +| | authentication, XN, WXN, security hardening | +| | techniques. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 07 | ++========================+====================================================+ +| Threat | **A malicious endpoint may forge a direct message | +| | request such that it reveals the internal state of | +| | another endpoint through the direct message | +| | response.** | +| | | +| | The secure partition or SPMC replies to a partition| +| | message by a direct message response with | +| | information which may reveal its internal state | +| | (e.g. partition message response outside of | +| | allowed bounds). | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SPMC or SP state | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Information discolure | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | Low (2) | Low (2) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | Medium (6) | Medium (6) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | Follow FF-A specification about state transitions, | +| | run time model, do input validation. | ++------------------------+----------------------------------------------------+ +| Mitigations | Yes. For the specific case of direct requests | +| implemented? | targeting the SPMC, the latter is hardened to | +| | prevent its internal state or the state of an SP | +| | to be revealed through a direct message response. | +| | Further FF-A v1.1 guidance about run time models | +| | and partition states is followed. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 08 | ++========================+====================================================+ +| Threat | **Probing the FF-A communication between | +| | endpoints.** | +| | | +| | SPMC and SPs are typically loaded to external | +| | memory (protected by a TrustZone memory | +| | controller). A malicious agent may use non invasive| +| | methods to probe the external memory bus and | +| | extract the traffic between an SP and the SPMC or | +| | among SPs when shared buffers are held in external | +| | memory. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF7 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SP/SPMC state, SP/SPMC secrets | ++------------------------+----------------------------------------------------+ +| Threat Agent | Hardware attack | ++------------------------+----------------------------------------------------+ +| Threat Type | Information disclosure | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | Low (2) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | Medium (6) | Medium (9) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | Implement DRAM protection techniques using | +| | hardware countermeasures at platform or chip level.| ++------------------------+--------------------------+-------------------------+ +| Mitigations | Platform specific. | +| implemented? | | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 09 | ++========================+====================================================+ +| Threat | **A malicious agent may attempt revealing the SPMC | +| | state or secrets by the use of software-based cache| +| | side-channel attack techniques.** | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF7 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SP or SPMC state | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Information disclosure | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | Low (2) | Low (2) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | Medium (6) | Medium (6) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | The SPMC may be hardened further with SW | +| | mitigations (e.g. speculation barriers) for the | +| | cases not covered in HW. Usage of hardened | +| | compilers and appropriate options, code inspection | +| | are recommended ways to mitigate Spectre types of | +| | attacks. | ++------------------------+----------------------------------------------------+ +| Mitigations | No. | +| implemented? | | ++------------------------+----------------------------------------------------+ + + ++------------------------+----------------------------------------------------+ +| ID | 10 | ++========================+====================================================+ +| Threat | **A malicious endpoint may attempt flooding the | +| | SPMC with requests targeting a service within an | +| | endpoint such that it denies another endpoint to | +| | access this service.** | +| | | +| | Similarly, the malicious endpoint may target a | +| | a service within an endpoint such that the latter | +| | is unable to request services from another | +| | endpoint. | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SPMC state, Scheduling cycles | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Denial of service | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | Medium (9) | Medium (9) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | Bounding the time for operations to complete can | +| | be achieved by the usage of a trusted watchdog. | +| | Other quality of service monitoring can be achieved| +| | in the SPMC such as counting a number of operations| +| | in a limited timeframe. | ++------------------------+----------------------------------------------------+ +| Mitigations | Platform specific. | +| implemented? | | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 11 | ++========================+====================================================+ +| Threat | **Denying a lender endpoint to make progress if | +| | borrower endpoint encountered a fatal exception. | +| | Denying a new sender endpoint to make progress | +| | if receiver encountered a fatal exception.** | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | Shared resources, Scheduling cycles. | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Denial of service | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | Medium (3) | Medium (3) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | Medium (9) | Medium (9) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | SPMC must be able to detect fatal error in SP and | +| | take ownership of shared resources. It should | +| | be able to relinquish the access to shared memory | +| | regions to allow lender to proceed. | +| | SPMC must return ABORTED if new direct requests are| +| | targeted to SP which has had a fatal error. | ++------------------------+----------------------------------------------------+ +| Mitigations | Platform specific. | +| implemented? | | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 12 | ++========================+====================================================+ +| Threat | **A malicious endpoint may attempt to donate, | +| | share, lend, relinquish or reclaim unauthorized | +| | memory region.** | ++------------------------+----------------------------------------------------+ +| Diagram Elements | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| Affected TF-A | SPMC | +| Components | | ++------------------------+----------------------------------------------------+ +| Assets | SP secrets, SPMC secrets, SP state, SPMC state | ++------------------------+----------------------------------------------------+ +| Threat Agent | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| Threat Type | Elevation of Privilege | ++------------------------+--------------------------+-------------------------+ +| Application | Server | Mobile | ++------------------------+--------------------------+-------------------------+ +| Impact | High (4) | High (4) | ++------------------------+--------------------------+-------------------------+ +| Likelihood | High (4) | High (4) | ++------------------------+--------------------------+-------------------------+ +| Total Risk Rating | High (16) | High (16) | ++------------------------+--------------------------+-------------------------+ +| Mitigations | Follow FF-A specification guidelines | +| | on Memory management transactions. | ++------------------------+----------------------------------------------------+ +| Mitigations | Yes. The SPMC tracks ownership and access state | +| implemented? | for memory transactions appropriately, and | +| | validating the same for all operations. | +| | SPMC follows FF-A v1.1 | +| | guidance for memory transaction lifecycle. | ++------------------------+----------------------------------------------------+ + +--------------- + +*Copyright (c) 2022, Arm Limited. All rights reserved.* + +.. _Arm Firmware Framework for Arm A-profile: https://developer.arm.com/docs/den0077/latest +.. _EL3 Secure Partition Manager: ../components/el3-spmc.html +.. _Generic TF-A threat model: ./threat_model.html#threat-analysis +.. _FF-A ACS: https://github.com/ARM-software/ff-a-acs/releases diff --git a/docs/threat_model/threat_model_fvp_r.rst b/docs/threat_model/threat_model_fvp_r.rst new file mode 100644 index 0000000..c1462bb --- /dev/null +++ b/docs/threat_model/threat_model_fvp_r.rst @@ -0,0 +1,97 @@ +fvp_r-Platform Threat Model +*************************** + +************************ +Introduction +************************ +This document provides a threat model for TF-A fvp_r platform. + +************************ +Target of Evaluation +************************ +In this threat model, the target of evaluation is the fvp_r platform of Trusted +Firmware for A-class Processors (TF-A). The fvp_r platform provides limited +support of AArch64 R-class Processors (v8-R64). + +This is a delta document, only pointing out differences from the general TF-A +threat-model document, :ref:`Generic Threat Model` + +BL1 Only +======== +The most fundamental difference between the threat model for the current fvp_r +implementation compared to the general TF-A threat model, is that fvp_r is +currently limited to BL1 only. Any threats from the general TF-A threat model +unrelated to BL1 are therefore not relevant to the fvp_r implementation. + +The fvp_r BL1 implementation directly loads a customer/partner-defined runtime +system. The threat model for that runtime system, being partner-defined, is +out-of-scope for this threat-model. + +Relatedly, all exceptions, synchronous and asynchronous, are disabled during BL1 +execution. So, any references to exceptions are not relevant. + +EL3 is Unsupported and All Secure +================================= +v8-R64 cores do not support EL3, and (essentially) all operation is defined as +Secure-mode. Therefore: + + - Any threats regarding NS operation are not relevant. + + - Any mentions of SMCs are also not relevant. + + - Anything otherwise-relevant code running in EL3 is instead run in EL2. + +MPU instead of MMU +================== +v8-R64 cores, running in EL2, use an MPU for memory management, rather than an +MMU. The MPU in the fvp_r implementation is configured to function effectively +identically with the MMU for the usual BL1 implementation. There are +memory-map differences, but the MPU configuration is functionally equivalent. + +No AArch32 Support +================== +Another substantial difference between v8-A and v8-R64 cores is that v8-R64 does +not support AArch32. However, this is not believed to have any threat-modeling +ramifications. + + +Threat Assessment +================= +For this section, please reference the Threat Assessment under the general TF-A +threat-model document, :ref:`Generic Threat Model` + +The following threats from that document are still relevant to the fvp_r +implementation: + + - ID 01: An attacker can mangle firmware images to execute arbitrary code. + + - ID 03: An attacker can use Time-of-Check-Time-of-Use (TOCTOU) attack to + bypass image authentication during the boot process. + + - ID 04: An attacker with physical access can execute arbitrary image by + bypassing the signature verification stage using clock- or power-glitching + techniques. + + - ID 05: Information leak via UART logs such as crashes + + - ID 06: An attacker can read sensitive data and execute arbitrary code + through the external debug and trace interface. + + - ID 08: Memory corruption due to memory overflows and lack of boundary + checking when accessing resources could allow an attacker to execute + arbitrary code, modify some state variable to change the normal flow of + the program, or leak sensitive. + + - ID 11: Misconfiguration of the Memory Protection Unit (MPU) may allow + normal world software to access sensitive data or execute arbitrary code. + Arguably, MPUs having fewer memory regions, there may be a temptation to + share memory regions, making this a greater threat. However, since the + fvp_r implementation is limited to BL1, since BL1's regions are fixed, + and since the MPU configuration is equivalent with that for the fvp + platform and others, this is not expected to be a concern. + + + +-------------- + +*Copyright (c) 2021, Arm Limited. All rights reserved.* diff --git a/docs/threat_model/threat_model_spm.rst b/docs/threat_model/threat_model_spm.rst new file mode 100644 index 0000000..98dbf76 --- /dev/null +++ b/docs/threat_model/threat_model_spm.rst @@ -0,0 +1,1161 @@ +SPMC Threat Model +***************** + +************************ +Introduction +************************ +This document provides a threat model for the TF-A `Secure Partition Manager`_ +(SPM) implementation or more generally the S-EL2 reference firmware running on +systems implementing the FEAT_SEL2 (formerly Armv8.4 Secure EL2) architecture +extension. The SPM implementation is based on the `Arm Firmware Framework for +Arm A-profile`_ specification. + +In brief, the broad FF-A specification and S-EL2 firmware implementation +provide: + +- Isolation of mutually mistrusting SW components, or endpoints in the FF-A + terminology. +- Distinct sandboxes in the secure world called secure partitions. This permits + isolation of services from multiple vendors. +- A standard protocol for communication and memory sharing between FF-A + endpoints. +- Mutual isolation of the normal world and the secure world (e.g. a Trusted OS + is prevented to map an arbitrary NS physical memory region such as the kernel + or the Hypervisor). + +************************ +Target of Evaluation +************************ +In this threat model, the target of evaluation is the S-EL2 firmware or the +``Secure Partition Manager Core`` component (SPMC). +The monitor and SPMD at EL3 are covered by the `Generic TF-A threat model`_. + +The scope for this threat model is: + +- The TF-A implementation for the S-EL2 SPMC based on the Hafnium hypervisor + running in the secure world of TrustZone (at S-EL2 exception level). + The threat model is not related to the normal world Hypervisor or VMs. + The S-EL1 SPMC solution is not covered. +- The implementation complies with the FF-A v1.0 specification, and a few + features of FF-A v1.1 specification. +- Secure partitions are statically provisioned at boot time. +- Focus on the run-time part of the life-cycle (no specific emphasis on boot + time, factory firmware provisioning, firmware udpate etc.) +- Not covering advanced or invasive physical attacks such as decapsulation, + FIB etc. +- Assumes secure boot or in particular TF-A trusted boot (TBBR or dual CoT) is + enabled. An attacker cannot boot arbitrary images that are not approved by the + SiP or platform providers. + +Data Flow Diagram +====================== +Figure 1 shows a high-level data flow diagram for the SPM split into an SPMD +component at EL3 and an SPMC component at S-EL2. The SPMD mostly acts as a +relayer/pass-through between the normal world and the secure world. It is +assumed to expose small attack surface. + +A description of each diagram element is given in Table 1. In the diagram, the +red broken lines indicate trust boundaries. + +Components outside of the broken lines are considered untrusted. + +.. uml:: ../resources/diagrams/plantuml/spm_dfd.puml + :caption: Figure 1: SPMC Data Flow Diagram + +.. table:: Table 1: SPMC Data Flow Diagram Description + + +---------------------+--------------------------------------------------------+ + | Diagram Element | Description | + +=====================+========================================================+ + | ``DF1`` | SP to SPMC communication. FF-A function invocation or | + | | implementation-defined Hypervisor call. | + +---------------------+--------------------------------------------------------+ + | ``DF2`` | SPMC to SPMD FF-A call. | + +---------------------+--------------------------------------------------------+ + | ``DF3`` | SPMD to NS forwarding. | + +---------------------+--------------------------------------------------------+ + | ``DF4`` | SP to SP FF-A direct message request/response. | + | | Note as a matter of simplifying the diagram | + | | the SP to SP communication happens through the SPMC | + | | (SP1 performs a direct message request to the | + | | SPMC targeting SP2 as destination. And similarly for | + | | the direct message response from SP2 to SP1). | + +---------------------+--------------------------------------------------------+ + | ``DF5`` | HW control. | + +---------------------+--------------------------------------------------------+ + | ``DF6`` | Bootloader image loading. | + +---------------------+--------------------------------------------------------+ + | ``DF7`` | External memory access. | + +---------------------+--------------------------------------------------------+ + +********************* +Threat Analysis +********************* + +This threat model follows a similar methodology to the `Generic TF-A threat model`_. +The following sections define: + +- Trust boundaries +- Assets +- Theat agents +- Threat types + +Trust boundaries +============================ + +- Normal world is untrusted. +- Secure world and normal world are separate trust boundaries. +- EL3 monitor, SPMD and SPMC are trusted. +- Bootloaders (in particular BL1/BL2 if using TF-A) and run-time BL31 are + implicitely trusted by the usage of secure boot. +- EL3 monitor, SPMD, SPMC do not trust SPs. + +.. figure:: ../resources/diagrams/spm-threat-model-trust-boundaries.png + + Figure 2: Trust boundaries + +Assets +============================ + +The following assets are identified: + +- SPMC state. +- SP state. +- Information exchange between endpoints (partition messages). +- SPMC secrets (e.g. pointer authentication key when enabled) +- SP secrets (e.g. application keys). +- Scheduling cycles. +- Shared memory. + +Threat Agents +============================ + +The following threat agents are identified: + +- NS-Endpoint identifies a non-secure endpoint: normal world client at NS-EL2 + (Hypervisor) or NS-EL1 (VM or OS kernel). +- S-Endpoint identifies a secure endpoint typically a secure partition. +- Hardware attacks (non-invasive) requiring a physical access to the device, + such as bus probing or DRAM stress. + +Threat types +============================ + +The following threat categories as exposed in the `Generic TF-A threat model`_ +are re-used: + +- Spoofing +- Tampering +- Repudiation +- Information disclosure +- Denial of service +- Elevation of privileges + +Similarly this threat model re-uses the same threat risk ratings. The risk +analysis is evaluated based on the environment being ``Server`` or ``Mobile``. + +Threat Assessment +============================ + +The following threats are identified by applying STRIDE analysis on each diagram +element of the data flow diagram. + ++------------------------+----------------------------------------------------+ +| ID | 01 | ++========================+====================================================+ +| ``Threat`` | **An endpoint impersonates the sender or receiver | +| | FF-A ID in a direct request/response invocation.** | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMD, SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SP state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Spoofing | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------++----------------+---------------+ +| ``Impact`` | Critical(5) | Critical(5) | | ++------------------------+------------------++----------------+---------------+ +| ``Likelihood`` | Critical(5) | Critical(5) | | ++------------------------+------------------++----------------+---------------+ +| ``Total Risk Rating`` | Critical(25) | Critical(25) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC does not mitigate this threat. | +| | The guidance below is left for a system integrator | +| | to implemented as necessary. | +| | The SPMC must enforce checks in the direct message | +| | request/response interfaces such an endpoint cannot| +| | spoof the origin and destination worlds (e.g. a NWd| +| | originated message directed to the SWd cannot use a| +| | SWd ID as the sender ID). | +| | Additionally a software component residing in the | +| | SPMC can be added for the purpose of direct | +| | request/response filtering. | +| | It can be configured with the list of known IDs | +| | and about which interaction can occur between one | +| | and another endpoint (e.g. which NWd endpoint ID | +| | sends a direct request to which SWd endpoint ID). | +| | This component checks the sender/receiver fields | +| | for a legitimate communication between endpoints. | +| | A similar component can exist in the OS kernel | +| | driver, or Hypervisor although it remains untrusted| +| | by the SPMD/SPMC. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 02 | ++========================+====================================================+ +| ``Threat`` | **Tampering with memory shared between an endpoint | +| | and the SPMC.** | +| | A malicious endpoint may attempt tampering with its| +| | RX/TX buffer contents while the SPMC is processing | +| | it (TOCTOU). | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF3, DF4, DF7 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | Shared memory, Information exchange | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | High (4) | High (4) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | High (4) | High (4) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | High (16) | High (16) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | In context of FF-A v1.0 this is the case of sharing| +| | the RX/TX buffer pair and usage in the | +| | PARTITION_INFO_GET or mem sharing primitives. | +| | The SPMC must copy the contents of the TX buffer | +| | to an internal temporary buffer before processing | +| | its contents. The SPMC must implement hardened | +| | input validation on data transmitted through the TX| +| | buffer by an untrusted endpoint. | +| | The TF-A SPMC mitigates this threat by enforcing | +| | checks on data transmitted through RX/TX buffers. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 03 | ++========================+====================================================+ +| ``Threat`` | **An endpoint may tamper with its own state or the | +| | state of another endpoint.** | +| | A malicious endpoint may attempt violating: | +| | - its own or another SP state by using an unusual | +| | combination (or out-of-order) FF-A function | +| | invocations. | +| | This can also be an endpoint emitting | +| | FF-A function invocations to another endpoint while| +| | the latter is not in a state to receive it (e.g. a | +| | SP sends a direct request to the normal world early| +| | while the normal world is not booted yet). | +| | - the SPMC state itself by employing unexpected | +| | transitions in FF-A memory sharing, direct requests| +| | and responses, or handling of interrupts. | +| | This can be led by random stimuli injection or | +| | fuzzing. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMD, SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SP state, SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | High (4) | High (4) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | High (12) | High (12) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC provides mitigation against such | +| | threat by following the guidance for partition | +| | runtime models as described in FF-A v1.1 EAC0 spec.| +| | The SPMC performs numerous checks in runtime to | +| | prevent illegal state transitions by adhering to | +| | the partition runtime model. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 04 | ++========================+====================================================+ +| ``Threat`` | *An attacker may attempt injecting errors by the | +| | use of external DRAM stress techniques.** | +| | A malicious agent may attempt toggling an SP | +| | Stage-2 MMU descriptor bit within the page tables | +| | that the SPMC manages. This can happen in Rowhammer| +| | types of attack. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF7 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SP or SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | Hardware attack | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering | ++------------------------+------------------+---------------+-----------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+---------------+-----------------+ +| ``Impact`` | High (4) | High (4) | | ++------------------------+------------------+---------------+-----------------+ +| ``Likelihood`` | Low (2) | Medium (3) | | ++------------------------+------------------+---------------+-----------------+ +| ``Total Risk Rating`` | Medium (8) | High (12) | | ++------------------------+------------------+---------------+-----------------+ +| ``Mitigations`` | The TF-A SPMC does not provide mitigations to this | +| | type of attack. It can be addressed by the use of | +| | dedicated HW circuity or hardening at the chipset | +| | or platform level left to the integrator. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 05 | ++========================+====================================================+ +| ``Threat`` | **Protection of the SPMC from a DMA capable device | +| | upstream to an SMMU.** | +| | A device may attempt to tamper with the internal | +| | SPMC code/data sections. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF5 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC or SP state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering, Elevation of privileges | ++------------------------+------------------+---------------+-----------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+---------------+-----------------+ +| ``Impact`` | High (4) | High (4) | | ++------------------------+------------------+---------------+-----------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+---------------+-----------------+ +| ``Total Risk Rating`` | High (12) | High (12) | | ++------------------------+------------------+---------------+-----------------+ +| ``Mitigations`` | A platform may prefer assigning boot time, | +| | statically alocated memory regions through the SMMU| +| | configuration and page tables. The FF-A v1.1 | +| | specification provisions this capability through | +| | static DMA isolation. | +| | The TF-A SPMC does not mitigate this threat. | +| | It will adopt the static DMA isolation approach in | +| | a future release. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 06 | ++========================+====================================================+ +| ``Threat`` | **Replay fragments of past communication between | +| | endpoints.** | +| | A malicious endpoint may replay a message exchange | +| | that occured between two legitimate endpoint as | +| | a matter of triggering a malfunction or extracting | +| | secrets from the receiving endpoint. In particular | +| | the memory sharing operation with fragmented | +| | messages between an endpoint and the SPMC may be | +| | replayed by a malicious agent as a matter of | +| | getting access or gaining permissions to a memory | +| | region which does not belong to this agent. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF2, DF3 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | Information exchange | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Repdudiation | ++------------------------+------------------+---------------+-----------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+---------------+-----------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+---------------+-----------------+ +| ``Likelihood`` | High (4) | High (4) | | ++------------------------+------------------+---------------+-----------------+ +| ``Total Risk Rating`` | High (12) | High (12) | | ++------------------------+------------------+---------------+-----------------+ +| ``Mitigations`` | The TF-A SPMC does not mitigate this threat. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 07 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint may attempt to extract data | +| | or state information by the use of invalid or | +| | incorrect input arguments.** | +| | Lack of input parameter validation or side effects | +| | of maliciously forged input parameters might affect| +| | the SPMC. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMD, SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SP secrets, SPMC secrets, SP state, SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Information discolure | ++------------------------+------------------+---------------+-----------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+---------------+-----------------+ +| ``Impact`` | High (4) | High (4) | | ++------------------------+------------------+---------------+-----------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+---------------+-----------------+ +| ``Total Risk Rating`` | High (12) | High (12) | | ++------------------------+------------------+---------------+-----------------+ +| ``Mitigations`` | Secure Partitions must follow security standards | +| | and best practises as a way to mitigate the risk | +| | of common vulnerabilities to be exploited. | +| | The use of software (canaries) or hardware | +| | hardening techniques (XN, WXN, BTI, pointer | +| | authentication, MTE) helps detecting and stopping | +| | an exploitation early. | +| | The TF-A SPMC mitigates this threat by implementing| +| | stack protector, pointer authentication, BTI, XN, | +| | WXN, security hardening techniques. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 08 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint may forge a direct message | +| | request such that it reveals the internal state of | +| | another endpoint through the direct message | +| | response.** | +| | The secure partition or SPMC replies to a partition| +| | message by a direct message response with | +| | information which may reveal its internal state | +| | (.e.g. partition message response outside of | +| | allowed bounds). | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC or SP state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Information discolure | ++------------------------+------------------+---------------+-----------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+---------------+-----------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+---------------+-----------------+ +| ``Likelihood`` | Low (2) | Low (2) | | ++------------------------+------------------+---------------+-----------------+ +| ``Total Risk Rating`` | Medium (6) | Medium (6) | | ++------------------------+------------------+---------------+-----------------+ +| ``Mitigations`` | For the specific case of direct requests targeting | +| | the SPMC, the latter is hardened to prevent | +| | its internal state or the state of an SP to be | +| | revealed through a direct message response. | +| | Further, SPMC performs numerous checks in runtime | +| | on the basis of the rules established by partition | +| | runtime models to stop any malicious attempts by | +| | an endpoint to extract internal state of another | +| | endpoint. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 09 | ++========================+====================================================+ +| ``Threat`` | **Probing the FF-A communication between | +| | endpoints.** | +| | SPMC and SPs are typically loaded to external | +| | memory (protected by a TrustZone memory | +| | controller). A malicious agent may use non invasive| +| | methods to probe the external memory bus and | +| | extract the traffic between an SP and the SPMC or | +| | among SPs when shared buffers are held in external | +| | memory. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF7 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SP/SPMC state, SP/SPMC secrets | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | Hardware attack | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Information disclosure | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Low (2) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (6) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | It is expected the platform or chipset provides | +| | guarantees in protecting the DRAM contents. | +| | The TF-A SPMC does not mitigate this class of | +| | attack and this is left to the integrator. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 10 | ++========================+====================================================+ +| ``Threat`` | **A malicious agent may attempt revealing the SPMC | +| | state or secrets by the use of software-based cache| +| | side-channel attack techniques.** | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF7 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SP or SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Information disclosure | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Low (2) | Low (2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (6) | Medium (6) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | From an integration perspective it is assumed | +| | platforms consuming the SPMC component at S-EL2 | +| | (hence implementing the Armv8.4 FEAT_SEL2 | +| | architecture extension) implement mitigations to | +| | Spectre, Meltdown or other cache timing | +| | side-channel type of attacks. | +| | The TF-A SPMC implements one mitigation (barrier | +| | preventing speculation past exeception returns). | +| | The SPMC may be hardened further with SW | +| | mitigations (e.g. speculation barriers) for the | +| | cases not covered in HW. Usage of hardened | +| | compilers and appropriate options, code inspection | +| | are recommended ways to mitigate Spectre types of | +| | attacks. For non-hardened cores, the usage of | +| | techniques such a kernel page table isolation can | +| | help mitigating Meltdown type of attacks. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 11 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint may attempt flooding the | +| | SPMC with requests targeting a service within an | +| | endpoint such that it denies another endpoint to | +| | access this service.** | +| | Similarly, the malicious endpoint may target a | +| | a service within an endpoint such that the latter | +| | is unable to request services from another | +| | endpoint. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Denial of service | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (9) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC does not mitigate this threat. | +| | Bounding the time for operations to complete can | +| | be achieved by the usage of a trusted watchdog. | +| | Other quality of service monitoring can be achieved| +| | in the SPMC such as counting a number of operations| +| | in a limited timeframe. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 12 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint may attempt to allocate | +| | notifications bitmaps in the SPMC, through the | +| | FFA_NOTIFICATION_BITMAP_CREATE.** | +| | This might be an attempt to exhaust SPMC's memory, | +| | or to allocate a bitmap for a VM that was not | +| | intended to receive notifications from SPs. Thus | +| | creating the possibility for a channel that was not| +| | meant to exist. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Denial of service, Spoofing | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium(3) | Medium(3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium(3) | Medium(3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium(9) | Medium(9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC mitigates this threat by defining a | +| | a fixed size pool for bitmap allocation. | +| | It also limits the designated FF-A calls to be used| +| | from NWd endpoints. | +| | In the NWd the hypervisor is supposed to limit the | +| | access to the designated FF-A call. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 13 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint may attempt to destroy the | +| | notifications bitmaps in the SPMC, through the | +| | FFA_NOTIFICATION_BITMAP_DESTROY.** | +| | This might be an attempt to tamper with the SPMC | +| | state such that a partition isn't able to receive | +| | notifications. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Low(4) | Low(4) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC mitigates this issue by limiting the | +| | designated FF-A call to be issued by the NWd. | +| | Also, the notifications bitmap can't be destroyed | +| | if there are pending notifications. | +| | In the NWd, the hypervisor must restrict the | +| | NS-endpoints that can issue the designated call. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 14 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint might attempt to give | +| | permissions to an unintended sender to set | +| | notifications targeting another receiver using the | +| | FF-A call FFA_NOTIFICATION_BIND.** | +| | This might be an attempt to tamper with the SPMC | +| | state such that an unintended, and possibly | +| | malicious, communication channel is established. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering, Spoofing | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium(3) | Medium(3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium(6) | Medium(6) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC mitigates this by restricting | +| | designated FFA_NOTIFICATION_BIND call to be issued | +| | by the receiver only. The receiver is responsible | +| | for allocating the notifications IDs to one | +| | specific partition. | +| | Also, receivers that are not meant to receive | +| | notifications, must have notifications receipt | +| | disabled in the respective partition's manifest. | +| | As for calls coming from NWd, if the NWd VM has had| +| | its bitmap allocated at initialization, the TF-A | +| | SPMC can't guarantee this threat won't happen. | +| | The Hypervisor must mitigate in the NWd, similarly | +| | to SPMC for calls in SWd. Though, if the Hypervisor| +| | has been compromised, the SPMC won't be able to | +| | mitigate it for calls forwarded from NWd. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 15 | ++========================+====================================================+ +| ``Threat`` | **A malicious partition endpoint might attempt to | +| | set notifications that are not bound to it.** | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Spoofing | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Low(4) | Low(4) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC mitigates this by checking the | +| | sender's ID provided in the input to the call | +| | FFA_NOTIFICATION_SET. The SPMC keeps track of which| +| | notifications are bound to which sender, for a | +| | given receiver. If the sender is an SP, the | +| | provided sender ID must match the ID of the | +| | currently running partition. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 16 | ++========================+====================================================+ +| ``Threat`` | **A malicious partition endpoint might attempt to | +| | get notifications that are not targeted to it.** | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Spoofing | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Informational(1) | Informational(1)| | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC mitigates this by checking the | +| | receiver's ID provided in the input to the call | +| | FFA_NOTIFICATION_GET. The SPMC keeps track of which| +| | notifications are pending for each receiver. | +| | The provided receiver ID must match the ID of the | +| | currently running partition, if it is an SP. | +| | For calls forwarded from NWd, the SPMC will return | +| | the pending notifications if the receiver had its | +| | bitmap created, and has pending notifications. | +| | If Hypervisor or OS kernel are compromised, the | +| | SPMC won't be able to mitigate calls from rogue NWd| +| | endpoints. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 17 | ++========================+====================================================+ +| ``Threat`` | **A malicious partition endpoint might attempt to | +| | get the information about pending notifications, | +| | through the FFA_NOTIFICATION_INFO_GET call.** | +| | This call is meant to be used by the NWd FF-A | +| | driver. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Information disclosure | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium(3) | Medium(3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium(6) | Medium(6) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC mitigates this by returning error to | +| | calls made by SPs to FFA_NOTIFICATION_INFO_GET. | +| | If Hypervisor or OS kernel are compromised, the | +| | SPMC won't be able mitigate calls from rogue NWd | +| | endpoints. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 18 | ++========================+====================================================+ +| ``Threat`` | **A malicious partition endpoint might attempt to | +| | flood another partition endpoint with notifications| +| | hindering its operation.** | +| | The intent of the malicious endpoint could be to | +| | interfere with both the receiver's and/or primary | +| | endpoint execution, as they can both be preempted | +| | by the NPI and SRI, respectively. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF4 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state, SP state, CPU cycles | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | DoS | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Low(2) | Low(2) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium(3) | Medium(3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium(6) | Medium(6) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC does not mitigate this threat. | +| | However, the impact is limited due to the | +| | architecture: | +| | - Notifications are not queued, one that has been | +| | signaled needs to be retrieved by the receiver, | +| | until it can be sent again. | +| | - Both SRI and NPI can't be pended until handled | +| | which limits the amount of spurious interrupts. | +| | - A given receiver could only bind a maximum number| +| | of notifications to a given sender, within a given | +| | execution context. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 19 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint may abuse FFA_RUN call to | +| | resume or turn on other endpoint execution | +| | contexts, attempting to alter the internal state of| +| | SPMC and SPs, potentially leading to illegal state | +| | transitions and deadlocks.** | +| | An endpoint can call into another endpoint | +| | execution context using FFA_MSG_SEND_DIRECT_REQ | +| | ABI to create a call chain. A malicious endpoint | +| | could abuse this to form loops in a call chain that| +| | could lead to potential deadlocks. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF4 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC, SPMD | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state, SP state, Scheduling cycles | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering, Denial of Service | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (9) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC provides mitigation against such | +| | threats by following the guidance for partition | +| | runtime models as described in FF-A v1.1 EAC0 spec.| +| | The SPMC performs numerous checks in runtime to | +| | prevent illegal state transitions by adhering to | +| | the partition runtime model. Further, if the | +| | receiver endpoint is a predecessor of current | +| | endpoint in the present call chain, the SPMC denies| +| | any attempts to form loops by returning FFA_DENIED | +| | error code. Only the primary scheduler is allowed | +| | to turn on execution contexts of other partitions | +| | though SPMC does not have the ability to | +| | scrutinize its identity. Secure partitions have | +| | limited ability to resume execution contexts of | +| | other partitions based on the runtime model. Such | +| | attempts cannot compromise the integrity of the | +| | SPMC. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 20 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint can perform a | +| | denial-of-service attack by using FFA_INTERRUPT | +| | call that could attempt to cause the system to | +| | crash or enter into an unknown state as no physical| +| | interrupt could be pending for it to be handled in | +| | the SPMC.** | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF5 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC, SPMD | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state, SP state, Scheduling cycles | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint, S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering, Denial of Service | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (9) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC provides mitigation against such | +| | attack by detecting invocations from partitions | +| | and simply returning FFA_ERROR status interface. | +| | SPMC only allows SPMD to use FFA_INTERRUPT ABI to | +| | communicate a pending secure interrupt triggered | +| | while execution was in normal world. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 21 | ++========================+====================================================+ +| ``Threat`` | **A malicious secure endpoint might deactivate a | +| | (virtual) secure interrupt that was not originally | +| | signaled by SPMC, thereby attempting to alter the | +| | state of the SPMC and potentially lead to system | +| | crash.** | +| | SPMC maps the virtual interrupt ids to the physical| +| | interrupt ids to keep the implementation of virtual| +| | interrupt driver simple. | +| | Similarly, a malicious secure endpoint might invoke| +| | the deactivation ABI more than once for a secure | +| | interrupt. Moreover, a malicious secure endpoint | +| | might attempt to deactivate a (virtual) secure | +| | interrupt that was signaled to another endpoint | +| | execution context by the SPMC even before secure | +| | interrupt was handled. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF5 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state, SP state | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (9) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | At initialization, the TF-A SPMC parses the | +| | partition manifests to find the target execution | +| | context responsible for handling the various | +| | secure physical interrupts. The TF-A SPMC provides | +| | mitigation against above mentioned threats by: | +| | | +| | - Keeping track of each pending virtual interrupt | +| | signaled to an execution context of a secure | +| | secure partition. | +| | - Denying any deactivation call from SP if there is| +| | no pending physical interrupt mapped to the | +| | given virtual interrupt. | +| | - Denying any deactivation call from SP if the | +| | virtual interrupt has not been signaled to the | +| | current execution context. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 22 | ++========================+====================================================+ +| ``Threat`` | **A malicious secure endpoint might not deactivate | +| | a virtual interrupt signaled to it by the SPMC but | +| | perform secure interrupt signal completion. This | +| | attempt to corrupt the internal state of the SPMC | +| | could lead to an unknown state and further lead to | +| | system crash.** | +| | Similarly, a malicious secure endpoint could | +| | deliberately not perform either interrupt | +| | deactivation or interrupt completion signal. Since,| +| | the SPMC can only process one secure interrupt at a| +| | time, this could choke the system where all | +| | interrupts are indefinitely masked which could | +| | potentially lead to system crash or reboot. | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF5 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state, SP state, Scheduling cycles | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | S-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Tampering, Denial of Service | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (9) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC does not provide mitigation against | +| | such threat. This is a limitation of the current | +| | SPMC implementation and needs to be handled in the | +| | future releases. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 23 | ++========================+====================================================+ +| ``Threat`` | **A malicious endpoint could leverage non-secure | +| | interrupts to preempt a secure endpoint, thereby | +| | attempting to render it unable to handle a secure | +| | virtual interrupt targetted for it. This could lead| +| | to priority inversion as secure virtual interrupts | +| | are kept pending while non-secure interrupts are | +| | handled by normal world VMs.** | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF5 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC, SPMD | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state, SP state, Scheduling cycles | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Denial of Service | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (9) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC alone does not provide mitigation | +| | against such threats. System integrators must take | +| | necessary high level design decisions that takes | +| | care of interrupt prioritization. The SPMC performs| +| | its role of enabling SPs to specify appropriate | +| | action towards non-secure interrupt with the help | +| | of partition manifest based on the guidance in the | +| | FF-A v1.1 EAC0 specification. | ++------------------------+----------------------------------------------------+ + ++------------------------+----------------------------------------------------+ +| ID | 24 | ++========================+====================================================+ +| ``Threat`` | **A secure endpoint depends on primary scheduler | +| | for CPU cycles. A malicious endpoint could delay | +| | the secure endpoint from being scheduled. Secure | +| | interrupts, if not handled timely, could compromise| +| | the state of SP and SPMC, thereby rendering the | +| | system unresponsive.** | ++------------------------+----------------------------------------------------+ +| ``Diagram Elements`` | DF1, DF2, DF3, DF5 | ++------------------------+----------------------------------------------------+ +| ``Affected TF-A | SPMC, SPMD | +| Components`` | | ++------------------------+----------------------------------------------------+ +| ``Assets`` | SPMC state, SP state, Scheduling cycles | ++------------------------+----------------------------------------------------+ +| ``Threat Agent`` | NS-Endpoint | ++------------------------+----------------------------------------------------+ +| ``Threat Type`` | Denial of Service | ++------------------------+------------------+-----------------+---------------+ +| ``Application`` | ``Server`` | ``Mobile`` | | ++------------------------+------------------+-----------------+---------------+ +| ``Impact`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Likelihood`` | Medium (3) | Medium (3) | | ++------------------------+------------------+-----------------+---------------+ +| ``Total Risk Rating`` | Medium (9) | Medium (9) | | ++------------------------+------------------+-----------------+---------------+ +| ``Mitigations`` | The TF-A SPMC does not provide full mitigation | +| | against such threats. However, based on the | +| | guidance provided in the FF-A v1.1 EAC0 spec, SPMC | +| | provisions CPU cycles to run a secure endpoint | +| | execution context in SPMC schedule mode which | +| | cannot be preempted by a non-secure interrupt. | +| | This reduces the dependency on primary scheduler | +| | for cycle allocation. Moreover, all further | +| | interrupts are masked until pending secure virtual | +| | interrupt on current CPU is handled. This allows SP| +| | execution context to make progress even upon being | +| | interrupted. | ++------------------------+----------------------------------------------------+ + +-------------- + +*Copyright (c) 2021-2022, Arm Limited. All rights reserved.* + +.. _Arm Firmware Framework for Arm A-profile: https://developer.arm.com/docs/den0077/latest +.. _Secure Partition Manager: ../components/secure-partition-manager.html +.. _Generic TF-A threat model: ./threat_model.html#threat-analysis +.. _FF-A ACS: https://github.com/ARM-software/ff-a-acs/releases |