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Bugzilla: 1053599
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Upstream-status: 3.13 and 3.12.8
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From 26bef1318adc1b3a530ecc807ef99346db2aa8b0 Mon Sep 17 00:00:00 2001
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From: Linus Torvalds <torvalds@linux-foundation.org>
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Date: Sat, 11 Jan 2014 19:15:52 -0800
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Subject: x86, fpu, amd: Clear exceptions in AMD FXSAVE workaround
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From: Linus Torvalds <torvalds@linux-foundation.org>
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commit 26bef1318adc1b3a530ecc807ef99346db2aa8b0 upstream.
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Before we do an EMMS in the AMD FXSAVE information leak workaround we
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need to clear any pending exceptions, otherwise we trap with a
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floating-point exception inside this code.
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Reported-by: halfdog <me@halfdog.net>
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Tested-by: Borislav Petkov <bp@suse.de>
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Link: http://lkml.kernel.org/r/CA%2B55aFxQnY_PCG_n4=0w-VG=YLXL-yr7oMxyy0WU2gCBAf3ydg@mail.gmail.com
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Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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arch/x86/include/asm/fpu-internal.h | 13 +++++++------
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1 file changed, 7 insertions(+), 6 deletions(-)
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--- a/arch/x86/include/asm/fpu-internal.h
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+++ b/arch/x86/include/asm/fpu-internal.h
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@@ -293,12 +293,13 @@ static inline int restore_fpu_checking(s
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/* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception
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is pending. Clear the x87 state here by setting it to fixed
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values. "m" is a random variable that should be in L1 */
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- alternative_input(
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- ASM_NOP8 ASM_NOP2,
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- "emms\n\t" /* clear stack tags */
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- "fildl %P[addr]", /* set F?P to defined value */
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- X86_FEATURE_FXSAVE_LEAK,
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- [addr] "m" (tsk->thread.fpu.has_fpu));
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+ if (unlikely(static_cpu_has(X86_FEATURE_FXSAVE_LEAK))) {
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+ asm volatile(
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+ "fnclex\n\t"
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+ "emms\n\t"
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+ "fildl %P[addr]" /* set F?P to defined value */
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+ : : [addr] "m" (tsk->thread.fpu.has_fpu));
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+ }
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return fpu_restore_checking(&tsk->thread.fpu);
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}
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