x86: msr: fix bogus return values from rdmsr_safe/wrmsr_safe (08970fc4) · Commits · 戴 / test

Impact: bogus error codes (+other?) on x86-64 The rdmsr_safe/wrmsr_safe routines have macros for the handling of the edx:eax arguments. Those macros take a variable number of assembly arguments. This is rather inherently incompatible with using %digit-style escapes in the inline assembly; replace those with %[name]-style escapes. This fixes miscompilation on x86-64, which at the very least caused bogus return values. It is possible that this could also corrupt the return value; I am not sure. Signed-off-by:

H. Peter Anvin <hpa@zytor.com>

include/asm-x86/msr.h

+8 −8

Original line number	Diff line number	Diff line
		@@ -52,14 +52,14 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
		{
		DECLARE_ARGS(val, low, high);

		asm volatile("2: rdmsr ; xor %0,%0\n"
		asm volatile("2: rdmsr ; xor %[err],%[err]\n"
		"1:\n\t"
		".section .fixup,\"ax\"\n\t"
		"3: mov %3,%0 ; jmp 1b\n\t"
		"3: mov %[fault],%[err] ; jmp 1b\n\t"
		".previous\n\t"
		_ASM_EXTABLE(2b, 3b)
		: "=r" (*err), EAX_EDX_RET(val, low, high)
		: "c" (msr), "i" (-EFAULT));
		: [err] "=r" (*err), EAX_EDX_RET(val, low, high)
		: "c" (msr), [fault] "i" (-EFAULT));
		return EAX_EDX_VAL(val, low, high);
		}

		@@ -73,15 +73,15 @@ static inline int native_write_msr_safe(unsigned int msr,
		unsigned low, unsigned high)
		{
		int err;
		asm volatile("2: wrmsr ; xor %0,%0\n"
		asm volatile("2: wrmsr ; xor %[err],%[err]\n"
		"1:\n\t"
		".section .fixup,\"ax\"\n\t"
		"3: mov %4,%0 ; jmp 1b\n\t"
		"3: mov %[fault],%[err] ; jmp 1b\n\t"
		".previous\n\t"
		_ASM_EXTABLE(2b, 3b)
		: "=a" (err)
		: [err] "=a" (err)
		: "c" (msr), "0" (low), "d" (high),
		"i" (-EFAULT)
		[fault] "i" (-EFAULT)
		: "memory");
		return err;
		}

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