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arch: arm: re-program MPU stack guard upon userspace enter

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Before entering userspace, the MPU stack guard is
configured to guard the default (i.e. afterwards, the "user")
thread stack, as the privileged stack has not yet been set. Upon
entering userspace the MPU stack guard needs to be re-programmed
to the privileged stack, otherwise, there is a risk that the
first system call might be serviced without privileged stack
protection, if it occurs before any context-switch. This commit
fixes this issue, by calling configure_mpu_stack_guard(..) upon
userspace entering.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
This commit is contained in:
Ioannis Glaropoulos 2018-10-09 23:05:13 +02:00 committed by Maureen Helm
parent 99b5c65edb
commit 3fb6ea210a
1 changed files with 9 additions and 0 deletions
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9
arch/arm/core/userspace.S
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@ -40,6 +40,15 @@ SECTION_FUNC(TEXT,_arm_userspace_enter)
/* move user_entry to lr */
mov lr, r0
#if defined (CONFIG_MPU_STACK_GUARD)
/* Re-program MPU to guard the privileged stack. */
push {r1,r2,r3,lr}
ldr r0, =_kernel
ldr r0, [r0, #_kernel_offset_to_current]
bl configure_mpu_stack_guard
pop {r1,r2,r3,lr}
#endif
/* set stack to priviliged stack */
ldr r0, =_kernel
ldr r0, [r0, #_kernel_offset_to_current]