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Use highest numbered MPU regions for kernel

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ARMv7-M allows overlapping MPU regions. When 2 MPU regions overlap, the
MPU configuration of the higher numbered MPU region is applied. For
example, if a memory area is covered by 2 MPU regions 0 and 1, the
memory permissions for MPU region 1 are applied.

We use 5 MPU regions for kernel code and kernel data protections and
leave the remaining for the application writer. We were using lowest
numbered MPU regions (0-4) for kernel protections and leaving the
remaining for the application writer. The application writer could
configure those higher numbered MPU regions to override kernel
protections.

This commit changes the code to use highest numbered MPU regions for
kernel protections and leave the remaining for the application writer.
This ensures that the application writer cannot override kernel
protections.

We thank the SecLab team at Northeastern University for reporting this
issue.

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>
This commit is contained in:
Gaurav Aggarwal 2022-09-07 14:47:14 +05:30 • committed by Gaurav-Aggarwal-AWS
parent ca099b9e9b
commit ea9c26f524
8 changed files with 79 additions and 134 deletions
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27
portable/GCC/ARM_CM3_MPU/port.c
View file

@ -756,7 +756,7 @@ void vPortStoreTaskMPUSettings( xMPU_SETTINGS * xMPUSettings,
xMPUSettings->xRegion[ 0 ].ulRegionBaseAddress =
( ( uint32_t ) __SRAM_segment_start__ ) | /* Base address. */
( portMPU_REGION_VALID ) |
( portSTACK_REGION );
( portSTACK_REGION ); /* Region number. */
xMPUSettings->xRegion[ 0 ].ulRegionAttribute =
( portMPU_REGION_READ_WRITE ) |
@ -764,23 +764,10 @@ void vPortStoreTaskMPUSettings( xMPU_SETTINGS * xMPUSettings,
( prvGetMPURegionSizeSetting( ( uint32_t ) __SRAM_segment_end__ - ( uint32_t ) __SRAM_segment_start__ ) ) |
( portMPU_REGION_ENABLE );
/* Re-instate the privileged only RAM region as xRegion[ 0 ] will have
* just removed the privileged only parameters. */
xMPUSettings->xRegion[ 1 ].ulRegionBaseAddress =
( ( uint32_t ) __privileged_data_start__ ) | /* Base address. */
( portMPU_REGION_VALID ) |
( portSTACK_REGION + 1 );
xMPUSettings->xRegion[ 1 ].ulRegionAttribute =
( portMPU_REGION_PRIVILEGED_READ_WRITE ) |
( portMPU_REGION_CACHEABLE_BUFFERABLE ) |
prvGetMPURegionSizeSetting( ( uint32_t ) __privileged_data_end__ - ( uint32_t ) __privileged_data_start__ ) |
( portMPU_REGION_ENABLE );
/* Invalidate all other regions. */
for( ul = 2; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
/* Invalidate user configurable regions. */
for( ul = 1UL; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
{
xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( portSTACK_REGION + ul ) | portMPU_REGION_VALID;
xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( ( ul - 1UL ) | portMPU_REGION_VALID );
xMPUSettings->xRegion[ ul ].ulRegionAttribute = 0UL;
}
}
@ -807,7 +794,7 @@ void vPortStoreTaskMPUSettings( xMPU_SETTINGS * xMPUSettings,
lIndex = 0;
for( ul = 1; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
for( ul = 1UL; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
{
if( ( xRegions[ lIndex ] ).ulLengthInBytes > 0UL )
{
@ -817,7 +804,7 @@ void vPortStoreTaskMPUSettings( xMPU_SETTINGS * xMPUSettings,
xMPUSettings->xRegion[ ul ].ulRegionBaseAddress =
( ( uint32_t ) xRegions[ lIndex ].pvBaseAddress ) |
( portMPU_REGION_VALID ) |
( portSTACK_REGION + ul ); /* Region number. */
( ul - 1UL ); /* Region number. */
xMPUSettings->xRegion[ ul ].ulRegionAttribute =
( prvGetMPURegionSizeSetting( xRegions[ lIndex ].ulLengthInBytes ) ) |
@ -827,7 +814,7 @@ void vPortStoreTaskMPUSettings( xMPU_SETTINGS * xMPUSettings,
else
{
/* Invalidate the region. */
xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( portSTACK_REGION + ul ) | portMPU_REGION_VALID;
xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( ( ul - 1UL ) | portMPU_REGION_VALID );
xMPUSettings->xRegion[ ul ].ulRegionAttribute = 0UL;
}