[ 119/143] x86, fpu, amd: Clear exceptions in AMD FXSAVE workaround

Willy Tarreau
2014-05-12T01:45:25Z

From: Linus Torvalds <torvalds@linux-foundation.org>

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>
(cherry picked from commit 26bef1318adc1b3a530ecc807ef99346db2aa8b0)
[wt: in 2.6.32, patch applies to arch/x86/include/asm/i387.h. There's
no static_cpu_has() so we use boot_cpu_has() like other kernels do
with gcc3.
]
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
arch/x86/include/asm/i387.h | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index 0b20bbb..cb42fad 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -242,12 +242,13 @@ clear_state:
/* 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. safe_address is a random variable that should be in L1 */
- alternative_input(
- GENERIC_NOP8 GENERIC_NOP2,
- "emms\n\t" /* clear stack tags */
- "fildl %[addr]", /* set F?P to defined value */
- X86_FEATURE_FXSAVE_LEAK,
- [addr] "m" (safe_address));
+ if (unlikely(boot_cpu_has(X86_FEATURE_FXSAVE_LEAK))) {
+ asm volatile(
+ "fnclex\n\t"
+ "emms\n\t"
+ "fildl %[addr]" /* set F?P to defined value */
+ : : [addr] "m" (safe_address));
+ }
end:
task_thread_info(tsk)->status &= ~TS_USEDFPU;
}
--
1.7.12.2.21.g234cd45.dirty