Adding upstream version 2.8.0+dfsg.upstream/2.8.0+dfsgupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 650 insertions, 0 deletions

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+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