[PATCH 2/2] powerpc/32: stack protector: change the canary value per task
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. Cc: Nicolas Pitre Signed-off-by: Christophe Leroy --- arch/powerpc/kernel/asm-offsets.c | 3 +++ arch/powerpc/kernel/entry_32.S| 6 +- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index a51ae9b..ede2fc4 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -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 diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S index 3841d74..5742dbd 100644 --- a/arch/powerpc/kernel/entry_32.S +++ b/arch/powerpc/kernel/entry_32.S @@ -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 */ -- 2.1.0
[PATCH 2/2] powerpc/32: stack protector: change the canary value per task
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 --- 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
Re: [PATCH 2/2] powerpc/32: stack protector: change the canary value per task
On Mon, Sep 17, 2018 at 12:15:08PM +, Christophe Leroy wrote: > 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. By far the easiest is to have the canary at a fixed offset from r2. Segher