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Remove local stack variable form MPU wrappers

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It was possible for a third party that had already independently gained
the ability to execute injected code to achieve further privilege
escalation by branching directly inside a FreeRTOS MPU API wrapper
function with a manually crafted stack frame. This commit removes the
local stack variable `xRunningPrivileged` so that a manually crafted
stack frame cannot be used for privilege escalation by branching
directly inside a FreeRTOS MPU API wrapper.

We thank Certibit Consulting, LLC, Huazhong University of Science and
Technology and 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 19:49:48 +05:30 • committed by Gaurav-Aggarwal-AWS
parent c4ad77f694
commit 51ea2bfe62
7 changed files with 1642 additions and 497 deletions
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55
portable/RVDS/ARM_CM4_MPU/port.c
View file

@ -517,30 +517,55 @@ void vPortEndScheduler( void )
void vPortEnterCritical( void )
{
BaseType_t xRunningPrivileged;
xPortRaisePrivilege( xRunningPrivileged );
if( portIS_PRIVILEGED() == pdFALSE )
{
portRAISE_PRIVILEGE();
portMEMORY_BARRIER();
portDISABLE_INTERRUPTS();
uxCriticalNesting++;
portDISABLE_INTERRUPTS();
uxCriticalNesting++;
portMEMORY_BARRIER();
vPortResetPrivilege( xRunningPrivileged );
portRESET_PRIVILEGE();
portMEMORY_BARRIER();
}
else
{
portDISABLE_INTERRUPTS();
uxCriticalNesting++;
}
}
/*-----------------------------------------------------------*/
void vPortExitCritical( void )
{
BaseType_t xRunningPrivileged;
xPortRaisePrivilege( xRunningPrivileged );
configASSERT( uxCriticalNesting );
uxCriticalNesting--;
if( uxCriticalNesting == 0 )
if( portIS_PRIVILEGED() == pdFALSE )
{
portENABLE_INTERRUPTS();
}
portRAISE_PRIVILEGE();
portMEMORY_BARRIER();
vPortResetPrivilege( xRunningPrivileged );
configASSERT( uxCriticalNesting );
uxCriticalNesting--;
if( uxCriticalNesting == 0 )
{
portENABLE_INTERRUPTS();
}
portMEMORY_BARRIER();
portRESET_PRIVILEGE();
portMEMORY_BARRIER();
}
else
{
configASSERT( uxCriticalNesting );
uxCriticalNesting--;
if( uxCriticalNesting == 0 )
{
portENABLE_INTERRUPTS();
}
}
}
/*-----------------------------------------------------------*/