arch: arm: enable PXN support for armv8.1-m #86942
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What is the change? This commit adds support for Armv8.1-M MPU architecture's PXN attribute. This includes support for configuring MPU regions with PXN via custom mpu_config, devicetree and static mpu_config. The existing MPU region attribute macros are updated to retain existing behaviour with this change with an addition of REGION_RAM_ATTR_PXN to be used if one needs to configure a RAM region with PXN MPU attribute. Why do we need this change? Armv8.1-M architecture introduced a new MPU region attribute called Privilege eXecute Never (PXN). If an MPU region is configured with the PXN attribute set and if the, processor attempts to execute code in this region while at privileged level, a Memory Management Fault exception is triggered. This ensures that specific tasks are executed only in unprivileged mode and helps in preventing secure privilege escalation attacks. Signed-off-by: Sudan Landge <sudan.landge@arm.com>
What is the change? - PXN attributes is set for static mpu regions such that __ramfunc and __ram_text_reloc having userspace code cannot be executed in privileged mode. - Updated the notable change section to inform about the change in behaviour of code executed from __ramfunc and __ram_text_reloc MPU regions. Why do we need this change? - The current static MPU regions allows executing userspace/unprivileged code from privileged mode which may not be expected and can lead to secure privileged escalation attacks. Signed-off-by: Sudan Landge <sudan.landge@arm.com>
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Adds a test to verify Armv8.1-M MPU architecture's PXN attribute. Verify PXN via static mpu config by utilizing existing __ramfunc MPU region Since previous commit changes the behaviour of __ramfunc region, executing userspace code in this region in privileged mode will result in an MPU fault while execution in unprivileged mode should work fine. Verify PXN via DT by creating a custom section in the unused SRAM region. Since the overlay sets the PXN attribute for the SRAM, executing code in this region in privileged mode will result in an MPU fault while, execution in unprivileged mode should work fine. Also, instead of testing DT config for each board, do it only for MPS3 boards that which can be tested with simulation. Signed-off-by: Sudan Landge <sudan.landge@arm.com>
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Mar 20, 2025
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What is the change?
This commit adds support for Armv8.1-M MPU architecture's PXN attribute.
This includes support for configuring MPU regions with PXN via
custom mpu_config, devicetree and static mpu_config.
The existing MPU region attribute macros are updated to retain existing
behaviour with this change with an addition of REGION_RAM_ATTR_PXN to be
used if one needs to configure a RAM region with PXN MPU attribute.
Why do we need this change?
Armv8.1-M architecture introduced a new MPU region attribute called
Privilege eXecute Never (PXN).
If an MPU region is configured with the PXN attribute set and if the,
processor attempts to execute code in this region while at
privileged level, a Memory Management Fault exception is triggered.
This ensures that specific tasks are executed only in unprivileged mode
and helps in preventing secure privilege escalation attacks.