Messages in this thread Patch in this message | | | From | Christophe Leroy <> | Subject | [PATCH 2/2] powerpc/32: stack protector: change the canary value per task | Date | Mon, 17 Sep 2018 12:15:08 +0000 (UTC) |
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Partially copied from commit df0698be14c66 ("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> --- I would have liked to use -mstack-protector-guard=tls -mstack-protector-guard-reg=r2 -mstack-protector-guard-offset=offsetof(struct task_struct, stack_canary) but I have not found how set the value of offsetof(struct task_struct, stack_canary) in Makefile. Any idea ?
arch/powerpc/kernel/asm-offsets.c | 3 +++ arch/powerpc/kernel/entry_32.S | 5 +++++ 2 files changed, 8 insertions(+)
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index 89cf15566c4e..cb02d23764ca 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -89,6 +89,9 @@ int main(void) DEFINE(THREAD_INFO_GAP, _ALIGN_UP(sizeof(struct thread_info), 16)); OFFSET(KSP_LIMIT, thread_struct, ksp_limit); #endif /* CONFIG_PPC64 */ +#ifdef CONFIG_CC_STACKPROTECTOR + DEFINE(TSK_STACK_CANARY, offsetof(struct task_struct, stack_canary)); +#endif #ifdef CONFIG_LIVEPATCH OFFSET(TI_livepatch_sp, thread_info, livepatch_sp); diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S index e58c3f467db5..0cdb4170a21d 100644 --- a/arch/powerpc/kernel/entry_32.S +++ b/arch/powerpc/kernel/entry_32.S @@ -721,6 +721,11 @@ 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 -- 2.13.3
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