Armv8.1-m: Add pacbti support

[AhmedIsmail02]

Description

In this Pull Request, Pointer Authentication, and Branch Target Identification Extension (PACBTI) support is added for Non-TrustZone variant of Cortex-M85 FreeRTOS-Kernel Port.

The PACBTI support is added for Arm Compiler For Embedded, and IAR toolchains only. The support in the kernel is not yet enabled for GNU toolchain due to known issues.

Blocks FreeRTOS-Partner-Supported-Demos PR!17

Test Steps

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

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[aggarg]

@AhmedIsmail02 Thank you for your contribution. I reviewed the code and I have the following suggestions -

1. Use portHAS_PACBTI_FEATURE instead of portPROCESSOR_VARIANT. This way we won't need to change code in multiple places when we add support for next processor variant which has PACBTI feature.
2. The current implementation seems to assume that the code is always used in CMake environment which is not true. I suggest to add configENABLE_PAC and configENABLE_BTI which can be set in FreeRTOSConfig.h. This is also consistent with the current flags configENABLE_FPU, configENABLE_MPU etc.
3. The change done in CM33_NTZ ports is also needed in CM33 ports.
4. Readability improvements.

All my suggestions are in this patch - 0001-Code-review-suggestions.patch. Please apply this patch.

Also, I think we do not need portable/CMakeLists.txt changes if we accept the above suggestions.

[AhmedIsmail02]

@aggarg Thank you for your suggestions. I do agree with almost all the code suggestions in the patch. Regarding the changes in portable/CMakeLists.txt which are related to the second suggestion, the reason why we chose to design our implementation based on CMake and not using the config solution is that some build flags (compiler and linker options) should be set based on the selected PACBTI configuration and these options also vary based on the selected compiler. These build options can't be controlled from the C code level and has to be added for the kernel and port targets to allow the compiler to insert the respective instructions based on the PACBTI configuration.
As an improvement we can minimize the number of macros checked for PAC and BTI enablement:

Before:
#if ( ( portARM_V_8_1_M_PACBTI_CONFIG == portARM_V_8_1_M_PACBTI_CONFIG_STANDARD ) || \ ( portARM_V_8_1_M_PACBTI_CONFIG == portARM_V_8_1_M_PACBTI_CONFIG_PACRET_LEAF_BTI ) ) || \ ( portARM_V_8_1_M_PACBTI_CONFIG == portARM_V_8_1_M_PACBTI_CONFIG_PACRET ) || \ ( portARM_V_8_1_M_PACBTI_CONFIG == portARM_V_8_1_M_PACBTI_CONFIG_PACRET_LEAF ) )

After:
#if ( portARM_V_8_1_M_PAC_ENABLED == 1 )

Thanks!

[aggarg]

Thank you @AhmedIsmail02 for looking at my suggestions.

These build options can't be controlled from the C code level and has to be added for the kernel and port targets to allow the compiler to insert the respective instructions based on the PACBTI configuration.

Understood. But can I not set the correct options for my compiler using my IDE and then set the FreeRTOS flags in FreeRTOSConfig.h? And with that we should be able to support CMake as well:

if(FREERTOS_ARM_V_8_1_M_PACBTI_CONFIG STREQUAL "ARM_V_8_1_M_PACBTI_CONFIG_PACRET_LEAF_BTI")
    if(${CMAKE_C_COMPILER_ID} STREQUAL "ARMClang")
        target_compile_options(freertos_kernel_port
            PUBLIC
                -mbranch-protection=bti+pac-ret+leaf
        )
        target_compile_definitions(freertos_kernel_port
            PUBLIC
                configENABLE_PAC=1
                configENABLE_BTI=1
        )

This way CMake users can still set FREERTOS_ARM_V_8_1_M_PACBTI_CONFIG to their desired values and do not need to worry about setting configENABLE_PAC and configENABLE_BTI in FreeRTOSConfig.h. Non CMake users, on the other hand, need to set correct compiler options and then set configENABLE_PAC and configENABLE_BTI in FreeRTOSConfig.h.

[aggarg]

Please apply the following patch to address CI header check failure - header_check.patch.

This will also require that this PR is merged - FreeRTOS/FreeRTOS#1285.

[AhmedIsmail02]

Hi @aggarg,
Thanks for the suggestions, the approach looks good to me as it ensures that both CMake and non-CMake based projects' behavior are aligned. I've applied the suggested changes for both the PACBTI configurations and the CI header check patch.

Thanks!

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud