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arch: arm: Flush pipeline after switching privilege levels

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During the transition of privilege levels while performing syscalls,
the ARM documentation recommends flushing the pipeline to avoid
pre-fetched instructions from being executed with the previous
privilege level.

The manual says:
   4.16 CONTROL register
   (...) after programming the CONTROL register, an ISB instruction
   should be used.
   (...) This is not implemented in the Cortex M0 processor.

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>
This commit is contained in:
Leandro Pereira 2018-04-06 16:03:47 -07:00 • committed by Kumar Gala
commit 4d5fbbc517
2 changed files with 24 additions and 0 deletions
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12
arch/arm/core/swap_helper.S
View file

@ -183,6 +183,12 @@ _thread_irq_disabled:
orr r3, r0 orr r3, r0
msr CONTROL, r3 msr CONTROL, r3
/* ISB is not strictly necessary here (stack pointer is not being
* touched), but it's recommended to avoid executing pre-fetched
* instructions with the previous privilege.
*/
isb
/* r2 contains k_thread */ /* r2 contains k_thread */
add r0, r2, #0 add r0, r2, #0
push {r2, lr} push {r2, lr}
@ -387,6 +393,12 @@ valid_syscall_id:
bic r2, #1 bic r2, #1
msr CONTROL, r2 msr CONTROL, r2
/* ISB is not strictly necessary here (stack pointer is not being
* touched), but it's recommended to avoid executing pre-fetched
* instructions with the previous privilege.
*/
isb
/* return from SVC to the modified LR - _arm_do_syscall */ /* return from SVC to the modified LR - _arm_do_syscall */
bx lr bx lr
#endif #endif

12
arch/arm/core/userspace.S
View file

@ -94,6 +94,12 @@ SECTION_FUNC(TEXT,_arm_userspace_enter)
orrs ip, ip, #1 orrs ip, ip, #1
msr CONTROL, ip msr CONTROL, ip
/* ISB is not strictly necessary here (stack pointer is not being
* touched), but it's recommended to avoid executing pre-fetched
* instructions with the previous privilege.
*/
isb
/* jump to _thread_entry entry */ /* jump to _thread_entry entry */
ldr ip, =_thread_entry ldr ip, =_thread_entry
bx ip bx ip
@ -173,6 +179,12 @@ dispatch_syscall:
orrs ip, ip, #1 orrs ip, ip, #1
msr CONTROL, ip msr CONTROL, ip
/* ISB is not strictly necessary here (stack pointer is not being
* touched), but it's recommended to avoid executing pre-fetched
* instructions with the previous privilege.
*/
isb
/* /*
* return back to original function that called SVC, add 1 to force thumb * return back to original function that called SVC, add 1 to force thumb
* mode * mode