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arch: arm: update arch.mode in user thread system calls

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This commit updates the thread.mode variable, in system
calls, whenever we modify the execution privilege level.
We need to do this, in order to be able to properly handle
context-switching triggered by ISRs, while doing the system
calls. The commit ensures that a context-switch, triggered
by an ISR during or after,a system call will preserve the
right privilege level.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
This commit is contained in:
Ioannis Glaropoulos 2019-04-01 12:40:23 +02:00 • committed by Anas Nashif
commit 4a58fa1186
2 changed files with 18 additions and 0 deletions
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9
arch/arm/core/swap_helper.S
View file

@ -418,6 +418,14 @@ _do_syscall:
ldr r6, =K_SYSCALL_BAD ldr r6, =K_SYSCALL_BAD
valid_syscall_id: valid_syscall_id:
push {r0, r1}
ldr r0, =_kernel
ldr r0, [r0, #_kernel_offset_to_current]
ldr r1, [r0, #_thread_offset_to_mode]
bic r1, #1
/* Store (privileged) mode in thread's mode state variable */
str r1, [r0, #_thread_offset_to_mode]
dsb
/* set mode to privileged, r2 still contains value from CONTROL */ /* set mode to privileged, r2 still contains value from CONTROL */
bic r2, #1 bic r2, #1
msr CONTROL, r2 msr CONTROL, r2
@ -427,6 +435,7 @@ valid_syscall_id:
* instructions with the previous privilege. * instructions with the previous privilege.
*/ */
isb isb
pop {r0, r1}
/* return from SVC to the modified LR - _arm_do_syscall */ /* return from SVC to the modified LR - _arm_do_syscall */
bx lr bx lr

9
arch/arm/core/userspace.S
View file

@ -242,6 +242,14 @@ dispatch_syscall:
ldr ip, [sp,#8] ldr ip, [sp,#8]
msr PSP, ip msr PSP, ip
push {r0, r1}
ldr r0, =_kernel
ldr r0, [r0, #_kernel_offset_to_current]
ldr r1, [r0, #_thread_offset_to_mode]
orrs r1, r1, #1
/* Store (unprivileged) mode in thread's mode state variable */
str r1, [r0, #_thread_offset_to_mode]
dsb
/* drop privileges by setting bit 0 in CONTROL */ /* drop privileges by setting bit 0 in CONTROL */
mrs ip, CONTROL mrs ip, CONTROL
orrs ip, ip, #1 orrs ip, ip, #1
@ -252,6 +260,7 @@ dispatch_syscall:
* instructions with the previous privilege. * instructions with the previous privilege.
*/ */
isb isb
pop {r0, r1}
/* Zero out volatile (caller-saved) registers so as to not leak state from /* Zero out volatile (caller-saved) registers so as to not leak state from
* kernel mode. The C calling convention for the syscall handler will * kernel mode. The C calling convention for the syscall handler will