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x86: conditionalize stack canary handling in hot path 

Impact: no unnecessary stack canary swapping during context switch

There's no point in moving stack_canary around during context switch
if it's not enabled.  Conditionalize it.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2009-01-20 12:29:19 +09:00
parent c6e50f93db
commit b4a8f7a262
1 changed files with 16 additions and 6 deletions
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22
arch/x86/include/asm/system.h
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@ -86,17 +86,28 @@ do { \
, "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
"r12", "r13", "r14", "r15"
#ifdef CONFIG_CC_STACKPROTECTOR
#define __switch_canary \
"movq %P[task_canary](%%rsi),%%r8\n\t" \
"movq %%r8,%%gs:%P[pda_canary]\n\t"
#define __switch_canary_param \
, [task_canary] "i" (offsetof(struct task_struct, stack_canary)) \
, [pda_canary] "i" (offsetof(struct x8664_pda, stack_canary))
#else /* CC_STACKPROTECTOR */
#define __switch_canary
#define __switch_canary_param
#endif /* CC_STACKPROTECTOR */
/* Save restore flags to clear handle leaking NT */
#define switch_to(prev, next, last) \
asm volatile(SAVE_CONTEXT \
asm volatile(SAVE_CONTEXT \
"movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \
"movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */ \
"call __switch_to\n\t" \
".globl thread_return\n" \
"thread_return:\n\t" \
"movq "__percpu_arg([current_task])",%%rsi\n\t" \
"movq %P[task_canary](%%rsi),%%r8\n\t" \
"movq %%r8,%%gs:%P[pda_canary]\n\t" \
__switch_canary \
"movq %P[thread_info](%%rsi),%%r8\n\t" \
LOCK_PREFIX "btr %[tif_fork],%P[ti_flags](%%r8)\n\t" \
"movq %%rax,%%rdi\n\t" \
@ -108,9 +119,8 @@ do { \
[ti_flags] "i" (offsetof(struct thread_info, flags)), \
[tif_fork] "i" (TIF_FORK), \
[thread_info] "i" (offsetof(struct task_struct, stack)), \
[task_canary] "i" (offsetof(struct task_struct, stack_canary)),\
[current_task] "m" (per_cpu_var(current_task)), \
[pda_canary] "i" (offsetof(struct x8664_pda, stack_canary))\
[current_task] "m" (per_cpu_var(current_task)) \
__switch_canary_param \
: "memory", "cc" __EXTRA_CLOBBER)
#endif