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x86/mmx: Use KFPU_387 for MMX string operations

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The default kernel_fpu_begin() doesn't work on systems that support XMM but
haven't yet enabled CR4.OSFXSR.  This causes crashes when _mmx_memcpy() is
called too early because LDMXCSR generates #UD when the aforementioned bit
is clear.

Fix it by using kernel_fpu_begin_mask(KFPU_387) explicitly.

Fixes: 7ad816762f9b ("x86/fpu: Reset MXCSR to default in kernel_fpu_begin()")
Reported-by: Krzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Krzysztof Piotr Olędzki <ole@ans.pl>
Tested-by: Krzysztof Mazur <krzysiek@podlesie.net>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/e7bf21855fe99e5f3baa27446e32623358f69e8d.1611205691.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski
2021-01-20 21:09:49 -08:00
committed by Borislav Petkov
parent e45122893a
commit 67de8dca50
1 changed files with 15 additions and 5 deletions
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20
arch/x86/lib/mmx_32.c
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@ -26,6 +26,16 @@
#include <asm/fpu/api.h>
#include <asm/asm.h>
/*
* Use KFPU_387. MMX instructions are not affected by MXCSR,
* but both AMD and Intel documentation states that even integer MMX
* operations will result in #MF if an exception is pending in FCW.
*
* EMMS is not needed afterwards because, after calling kernel_fpu_end(),
* any subsequent user of the 387 stack will reinitialize it using
* KFPU_387.
*/
void *_mmx_memcpy(void *to, const void *from, size_t len)
{
void *p;
@ -37,7 +47,7 @@ void *_mmx_memcpy(void *to, const void *from, size_t len)
p = to;
i = len >> 6; /* len/64 */
kernel_fpu_begin();
kernel_fpu_begin_mask(KFPU_387);
__asm__ __volatile__ (
"1: prefetch (%0)\n" /* This set is 28 bytes */
@ -127,7 +137,7 @@ static void fast_clear_page(void *page)
{
int i;
kernel_fpu_begin();
kernel_fpu_begin_mask(KFPU_387);
__asm__ __volatile__ (
" pxor %%mm0, %%mm0\n" : :
@ -160,7 +170,7 @@ static void fast_copy_page(void *to, void *from)
{
int i;
kernel_fpu_begin();
kernel_fpu_begin_mask(KFPU_387);
/*
* maybe the prefetch stuff can go before the expensive fnsave...
@ -247,7 +257,7 @@ static void fast_clear_page(void *page)
{
int i;
kernel_fpu_begin();
kernel_fpu_begin_mask(KFPU_387);
__asm__ __volatile__ (
" pxor %%mm0, %%mm0\n" : :
@ -282,7 +292,7 @@ static void fast_copy_page(void *to, void *from)
{
int i;
kernel_fpu_begin();
kernel_fpu_begin_mask(KFPU_387);
__asm__ __volatile__ (
"1: prefetch (%0)\n"