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Commit 26bef131 authored by Linus Torvalds's avatar Linus Torvalds Committed by H. Peter Anvin
Browse files

x86, fpu, amd: Clear exceptions in AMD FXSAVE workaround 



Before we do an EMMS in the AMD FXSAVE information leak workaround we
need to clear any pending exceptions, otherwise we trap with a
floating-point exception inside this code.

Reported-by: default avatarhalfdog <me@halfdog.net>
Tested-by: default avatarBorislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/CA%2B55aFxQnY_PCG_n4=0w-VG=YLXL-yr7oMxyy0WU2gCBAf3ydg@mail.gmail.com


Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 1739f09e

arch/x86/include/asm/fpu-internal.h

+7 −6
Original line number Diff line number Diff line
@@ -293,12 +293,13 @@ static inline int restore_fpu_checking(struct task_struct *tsk) 
	/* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception

	   is pending.  Clear the x87 state here by setting it to fixed

	   values. "m" is a random variable that should be in L1 */

	alternative_input(

		ASM_NOP8 ASM_NOP2,

		"emms\n\t"		/* clear stack tags */

		"fildl %P[addr]",	/* set F?P to defined value */

		X86_FEATURE_FXSAVE_LEAK,

		[addr] "m" (tsk->thread.fpu.has_fpu));

	if (unlikely(static_cpu_has(X86_FEATURE_FXSAVE_LEAK))) {

		asm volatile(

			"fnclex\n\t"

			"emms\n\t"

			"fildl %P[addr]"	/* set F?P to defined value */

			: : [addr] "m" (tsk->thread.fpu.has_fpu));

	}



	return fpu_restore_checking(&tsk->thread.fpu);

}