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>
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1 changed files with 16 additions and 6 deletions
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@ -86,17 +86,28 @@ do { \
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, "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
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"r12", "r13", "r14", "r15"
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#ifdef CONFIG_CC_STACKPROTECTOR
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#define __switch_canary \
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"movq %P[task_canary](%%rsi),%%r8\n\t" \
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"movq %%r8,%%gs:%P[pda_canary]\n\t"
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#define __switch_canary_param \
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, [task_canary] "i" (offsetof(struct task_struct, stack_canary)) \
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, [pda_canary] "i" (offsetof(struct x8664_pda, stack_canary))
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#else /* CC_STACKPROTECTOR */
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#define __switch_canary
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#define __switch_canary_param
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#endif /* CC_STACKPROTECTOR */
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/* Save restore flags to clear handle leaking NT */
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#define switch_to(prev, next, last) \
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asm volatile(SAVE_CONTEXT \
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asm volatile(SAVE_CONTEXT \
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"movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \
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"movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */ \
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"call __switch_to\n\t" \
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".globl thread_return\n" \
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"thread_return:\n\t" \
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"movq "__percpu_arg([current_task])",%%rsi\n\t" \
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"movq %P[task_canary](%%rsi),%%r8\n\t" \
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"movq %%r8,%%gs:%P[pda_canary]\n\t" \
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__switch_canary \
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"movq %P[thread_info](%%rsi),%%r8\n\t" \
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LOCK_PREFIX "btr %[tif_fork],%P[ti_flags](%%r8)\n\t" \
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"movq %%rax,%%rdi\n\t" \
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@ -108,9 +119,8 @@ do { \
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[ti_flags] "i" (offsetof(struct thread_info, flags)), \
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[tif_fork] "i" (TIF_FORK), \
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[thread_info] "i" (offsetof(struct task_struct, stack)), \
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[task_canary] "i" (offsetof(struct task_struct, stack_canary)),\
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[current_task] "m" (per_cpu_var(current_task)), \
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[pda_canary] "i" (offsetof(struct x8664_pda, stack_canary))\
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[current_task] "m" (per_cpu_var(current_task)) \
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__switch_canary_param \
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: "memory", "cc" __EXTRA_CLOBBER)
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#endif
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