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Merge "docs(spm): update threat model" into integration

pull/1990/head v2.8
Manish Pandey 2 years ago
committed by TrustedFirmware Code Review
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1 changed files with 283 additions and 14 deletions
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  1. 297
      docs/threat_model/threat_model_spm.rst

297
docs/threat_model/threat_model_spm.rst
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@ -258,7 +258,7 @@ element of the data flow diagram.
| | 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. a |
| | 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 |
@ -286,14 +286,12 @@ element of the data flow diagram.
+------------------------+------------------+-----------------+---------------+
| ``Total Risk Rating`` | High (12) | High (12) | |
+------------------------+------------------+-----------------+---------------+
| ``Mitigations`` | The SPMC may be vulnerable to invalid state |
| | transitions for itself or while handling an SP |
| | state. The FF-A v1.1 specification provides a |
| | guidance on those state transitions (run-time |
| | model). The TF-A SPMC will be hardened in future |
| | releases to follow this guidance. |
| | Additionally The TF-A SPMC mitigates the threat by |
| | runs of the Arm `FF-A ACS`_ compliance test suite. |
| ``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. |
+------------------------+----------------------------------------------------+
+------------------------+----------------------------------------------------+
@ -482,9 +480,11 @@ element of the data flow diagram.
| | 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 will be implemented in future |
| | TF-A SPMC releases. |
| | 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. |
+------------------------+----------------------------------------------------+
+------------------------+----------------------------------------------------+
@ -882,9 +882,278 @@ element of the data flow diagram.
| | 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, Arm Limited. All rights reserved.*
*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

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