0x00000020 embedded system_error ai_generated true

MPU fault: unprivileged access to privileged region at address 0x20001000

ID: embedded/arm-mpu-fault-unprivileged-access

Also available as: JSON · Markdown · 中文
88%Fix Rate
86%Confidence
1Evidence
2024-01-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
ARM Cortex-M7 r1p0 active — — —
FreeRTOS 10.4.6 with MPU support active — — —

Root Cause

MPU region configuration mismatch: code running in unprivileged mode attempted to read or write a memory region marked as privileged-only.

generic

中文

MPU区域配置不匹配：在非特权模式下运行的代码尝试读取或写入标记为仅特权访问的内存区域。

Official Documentation

https://developer.arm.com/documentation/den0013/latest/ARM-MPU

Workarounds

  1. 90% success Set MPU region attribute to 'privileged read-write, unprivileged execute never' for sensitive areas. Example: MPU->RBAR = (0x20001000 & MPU_RBAR_ADDR_Msk) | MPU_RBAR_VALID_Msk | (0 << MPU_RBAR_REGION_Pos); MPU->RASR = (0x3 << MPU_RASR_AP_Pos) | MPU_RASR_XN_Msk; 
    Set MPU region attribute to 'privileged read-write, unprivileged execute never' for sensitive areas. Example: MPU->RBAR = (0x20001000 & MPU_RBAR_ADDR_Msk) | MPU_RBAR_VALID_Msk | (0 << MPU_RBAR_REGION_Pos); MPU->RASR = (0x3 << MPU_RASR_AP_Pos) | MPU_RASR_XN_Msk;
  2. 82% success Switch offending task to privileged mode by setting configUSE_TASK_FPU_SUPPORT to 1 and using vTaskPrioritySet to adjust. 
    Switch offending task to privileged mode by setting configUSE_TASK_FPU_SUPPORT to 1 and using vTaskPrioritySet to adjust.

中文步骤

  1. Set MPU region attribute to 'privileged read-write, unprivileged execute never' for sensitive areas. Example: MPU->RBAR = (0x20001000 & MPU_RBAR_ADDR_Msk) | MPU_RBAR_VALID_Msk | (0 << MPU_RBAR_REGION_Pos); MPU->RASR = (0x3 << MPU_RASR_AP_Pos) | MPU_RASR_XN_Msk;
  2. Switch offending task to privileged mode by setting configUSE_TASK_FPU_SUPPORT to 1 and using vTaskPrioritySet to adjust.

Dead Ends

Common approaches that don't work:

  1. 85% fail

    Disabling MPU entirely removes protection but does not fix root cause; security or safety requirements may be violated.

  2. 95% fail

    Increasing stack size does not resolve MPU access violations; fault is due to privilege level, not stack depth.