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Commit b4a8f7a2 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
parent c6e50f93

arch/x86/include/asm/system.h

+16 −6
Original line number Diff line number Diff line
@@ -86,6 +86,18 @@ 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					  \
@@ -95,8 +107,7 @@ do { \ 
	     ".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