Commit 4630535c authored by Uros Bizjak's avatar Uros Bizjak Committed by Borislav Petkov
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x86/uaccess: Improve __try_cmpxchg64_user_asm() for x86_32 



Improve __try_cmpxcgh64_user_asm() for !CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT
by relaxing the output register constraint from "c" to "q" constraint,
which allows the compiler to choose between %ecx or %ebx register.

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarSean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220628161612.7993-1-ubizjak@gmail.com
parent 3163600c

arch/x86/include/asm/uaccess.h

+6 −5
Original line number Diff line number Diff line
@@ -448,7 +448,7 @@ do { \ 


#ifdef CONFIG_X86_32

/*

 * Unlike the normal CMPXCHG, hardcode ECX for both success/fail and error.

 * Unlike the normal CMPXCHG, use output GPR for both success/fail and error.

 * There are only six GPRs available and four (EAX, EBX, ECX, and EDX) are

 * hardcoded by CMPXCHG8B, leaving only ESI and EDI.  If the compiler uses

 * both ESI and EDI for the memory operand, compilation will fail if the error
@@ -461,11 +461,12 @@ do { \ 
	__typeof__(*(_ptr)) __new = (_new);				\

	asm volatile("\n"						\

		     "1: " LOCK_PREFIX "cmpxchg8b %[ptr]\n"		\

		     "mov $0, %%ecx\n\t"				\

		     "setz %%cl\n"					\

		     "mov $0, %[result]\n\t"				\

		     "setz %b[result]\n"				\

		     "2:\n"						\

		     _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG, %%ecx) \

		     : [result]"=c" (__result),				\

		     _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG,	\

					   %[result])			\

		     : [result] "=q" (__result),			\

		       "+A" (__old),					\

		       [ptr] "+m" (*_ptr)				\

		     : "b" ((u32)__new),				\