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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 |