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powerpc/32: Change the stack protector canary value per task

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Partially copied from commit df0698be14 ("ARM: stack protector:
change the canary value per task")

A new random value for the canary is stored in the task struct whenever
a new task is forked.  This is meant to allow for different canary values
per task.  On powerpc, GCC expects the canary value to be found in a global
variable called __stack_chk_guard.  So this variable has to be updated
with the value stored in the task struct whenever a task switch occurs.

Because the variable GCC expects is global, this cannot work on SMP
unfortunately.  So, on SMP, the same initial canary value is kept
throughout, making this feature a bit less effective although it is still
useful.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Christophe Leroy 2016-11-22 11:49:32 +01:00 committed by Michael Ellerman
parent 6533b7c16e
commit 902e06eb86
2 changed files with 8 additions and 1 deletions
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3
arch/powerpc/kernel/asm-offsets.c
View File

@ -91,6 +91,9 @@ int main(void)
DEFINE(TI_livepatch_sp, offsetof(struct thread_info, livepatch_sp));
#endif
#ifdef CONFIG_CC_STACKPROTECTOR
DEFINE(TSK_STACK_CANARY, offsetof(struct task_struct, stack_canary));
#endif
DEFINE(KSP, offsetof(struct thread_struct, ksp));
DEFINE(PT_REGS, offsetof(struct thread_struct, regs));
#ifdef CONFIG_BOOKE

6
arch/powerpc/kernel/entry_32.S
View File

@ -674,7 +674,11 @@ BEGIN_FTR_SECTION
mtspr SPRN_SPEFSCR,r0 /* restore SPEFSCR reg */
END_FTR_SECTION_IFSET(CPU_FTR_SPE)
#endif /* CONFIG_SPE */
#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
lwz r0,TSK_STACK_CANARY(r2)
lis r4,__stack_chk_guard@ha
stw r0,__stack_chk_guard@l(r4)
#endif
lwz r0,_CCR(r1)
mtcrf 0xFF,r0
/* r3-r12 are destroyed -- Cort */