Commit 67de8dca authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Borislav Petkov
Browse files

x86/mmx: Use KFPU_387 for MMX string operations 



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: 7ad81676 ("x86/fpu: Reset MXCSR to default in kernel_fpu_begin()")
Reported-by: default avatarKrzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Tested-by: default avatarKrzysztof Piotr Olędzki <ole@ans.pl>
Tested-by: default avatarKrzysztof Mazur <krzysiek@podlesie.net>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/e7bf21855fe99e5f3baa27446e32623358f69e8d.1611205691.git.luto@kernel.org
parent e4512289

arch/x86/lib/mmx_32.c

+15 −5
Original line number Diff line number Diff line
@@ -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"