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Fix portSWITCH_TO_USER_MODE() on Armv7-M MPU ports (#803)

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A task's privilege level is stored in ulTaskFlag member in the TCB. Current
implementation of portSWITCH_TO_USER_MODE() does not update this
flag but just lowers the processor's privilege level. This results in many
APIs incorrectly determining task's privilege level and access permissions -

- xPortIsAuthorizedToAccessBuffer
- xPortIsTaskPrivileged
- xPortIsAuthorizedToAccessKernelObject

This PR fixes the portSWITCH_TO_USER_MODE() implementation to correctly
update the ulTaskFlag member in the TCB before lowering the processor's
privilege level.
This commit is contained in:
Soren Ptak 2023-09-26 02:06:23 -07:00 • committed by GitHub
parent ac5deb155d
commit 84bdb05bd2
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GPG key ID: 4AEE18F83AFDEB23
8 changed files with 131 additions and 45 deletions
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47
portable/RVDS/ARM_CM4_MPU/port.c
View file

@ -219,6 +219,11 @@ BaseType_t xIsPrivileged( void );
*/
void vResetPrivilege( void );
/**
* @brief Make a task unprivileged.
*/
void vPortSwitchToUserMode( void );
/**
* @brief Enter critical section.
*/
@ -312,7 +317,7 @@ StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
}
else
{
xMPUSettings->ulTaskFlags &= ( ~portTASK_IS_PRIVILEGED_FLAG );
xMPUSettings->ulTaskFlags &= ( ~( portTASK_IS_PRIVILEGED_FLAG ) );
xMPUSettings->ulContext[ 0 ] = portINITIAL_CONTROL_IF_UNPRIVILEGED;
}
@ -1219,19 +1224,6 @@ __weak void vSetupTimerInterrupt( void )
}
/*-----------------------------------------------------------*/
__asm void vPortSwitchToUserMode( void )
{
/* *INDENT-OFF* */
PRESERVE8
mrs r0, control
orr r0, #1
msr control, r0
bx r14
/* *INDENT-ON* */
}
/*-----------------------------------------------------------*/
__asm void vPortEnableVFP( void )
{
/* *INDENT-OFF* */
@ -1349,10 +1341,10 @@ __asm BaseType_t xIsPrivileged( void )
PRESERVE8
mrs r0, control /* r0 = CONTROL. */
tst r0, #1 /* Perform r0 & 1 (bitwise AND) and update the conditions flag. */
tst r0, #1 /* Perform r0 & 1 (bitwise AND) and update the conditions flag. */
ite ne
movne r0, #0 /* CONTROL[0]!=0. Return false to indicate that the processor is not privileged. */
moveq r0, #1 /* CONTROL[0]==0. Return true to indicate that the processor is privileged. */
movne r0, #0 /* CONTROL[0]!=0. Return false to indicate that the processor is not privileged. */
moveq r0, #1 /* CONTROL[0]==0. Return true to indicate that the processor is privileged. */
bx lr /* Return. */
/* *INDENT-ON* */
}
@ -1363,14 +1355,27 @@ __asm void vResetPrivilege( void )
/* *INDENT-OFF* */
PRESERVE8
mrs r0, control /* r0 = CONTROL. */
orrs r0, #1 /* r0 = r0 | 1. */
msr control, r0 /* CONTROL = r0. */
bx lr /* Return. */
mrs r0, control /* r0 = CONTROL. */
orrs r0, #1 /* r0 = r0 | 1. */
msr control, r0 /* CONTROL = r0. */
bx lr /* Return. */
/* *INDENT-ON* */
}
/*-----------------------------------------------------------*/
void vPortSwitchToUserMode( void )
{
/* Load the current task's MPU settings from its TCB. */
xMPU_SETTINGS * xTaskMpuSettings = xTaskGetMPUSettings( NULL );
/* Mark the task as unprivileged. */
xTaskMpuSettings->ulTaskFlags &= ( ~( portTASK_IS_PRIVILEGED_FLAG ) );
/* Lower the processor's privilege level. */
vResetPrivilege();
}
/*-----------------------------------------------------------*/
void vPortStoreTaskMPUSettings( xMPU_SETTINGS * xMPUSettings,
const struct xMEMORY_REGION * const xRegions,
StackType_t * pxBottomOfStack,

18
portable/RVDS/ARM_CM4_MPU/portmacro.h
View file

@ -189,9 +189,6 @@ typedef unsigned long UBaseType_t;
#define portNUM_CONFIGURABLE_REGIONS ( configTOTAL_MPU_REGIONS - 5UL )
#define portTOTAL_NUM_REGIONS_IN_TCB ( portNUM_CONFIGURABLE_REGIONS + 1 ) /* Plus 1 to create space for the stack region. */
void vPortSwitchToUserMode( void );
#define portSWITCH_TO_USER_MODE() vPortSwitchToUserMode()
typedef struct MPU_REGION_REGISTERS
{
uint32_t ulRegionBaseAddress;
@ -356,24 +353,33 @@ extern void vPortExitCritical( void );
extern BaseType_t xIsPrivileged( void );
extern void vResetPrivilege( void );
extern void vPortSwitchToUserMode( void );
/**
* @brief Checks whether or not the processor is privileged.
*
* @return 1 if the processor is already privileged, 0 otherwise.
*/
#define portIS_PRIVILEGED() xIsPrivileged()
#define portIS_PRIVILEGED() xIsPrivileged()
/**
* @brief Raise an SVC request to raise privilege.
*/
#define portRAISE_PRIVILEGE() __asm { svc portSVC_RAISE_PRIVILEGE }
#define portRAISE_PRIVILEGE() __asm { svc portSVC_RAISE_PRIVILEGE }
/**
* @brief Lowers the privilege level by setting the bit 0 of the CONTROL
* register.
*/
#define portRESET_PRIVILEGE() vResetPrivilege()
#define portRESET_PRIVILEGE() vResetPrivilege()
/**
* @brief Make a task unprivileged.
*
* It must be called from privileged tasks only. Calling it from unprivileged
* task will result in a memory protection fault.
*/
#define portSWITCH_TO_USER_MODE() vPortSwitchToUserMode()
/*-----------------------------------------------------------*/
extern BaseType_t xPortIsTaskPrivileged( void );