Bugzilla: 1053599
Upstream-status: 3.13 and 3.12.8
From 26bef1318adc1b3a530ecc807ef99346db2aa8b0 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sat, 11 Jan 2014 19:15:52 -0800
Subject: x86, fpu, amd: Clear exceptions in AMD FXSAVE workaround
From: Linus Torvalds <torvalds@linux-foundation.org>
commit 26bef1318adc1b3a530ecc807ef99346db2aa8b0 upstream.
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: halfdog <me@halfdog.net>
Tested-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/CA%2B55aFxQnY_PCG_n4=0w-VG=YLXL-yr7oMxyy0WU2gCBAf3ydg@mail.gmail.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/fpu-internal.h | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -293,12 +293,13 @@ static inline int restore_fpu_checking(s
/* 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);
}