Re: [PATCH 3.12 69/72] Revert "fix minor infoleak in get_user_ex()"

[Linus Torvalds]

So a patch something like this might be a safe way to fix the
potential infoleak in older kernels.

THIS IS UNTESTED. It's a very obvious patch, though, so if it compiles
it probably works. It just initializes the output variable with 0 in
the inline asm description, instead of doing it in the exception
handler.

It will generate slightly worse code (a few unnecessary ALU
operations), but it doesn't have any interactions with the exception
handler implementation.

                  Linus
 arch/x86/include/asm/uaccess.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 5838fa911aa0..c2e06ee8b290 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -321,7 +321,7 @@ do {									\
 #define __get_user_asm_u64(x, ptr, retval, errret) \
 	 __get_user_asm(x, ptr, retval, "q", "", "=r", errret)
 #define __get_user_asm_ex_u64(x, ptr) \
-	 __get_user_asm_ex(x, ptr, "q", "", "=r")
+	 __get_user_asm_ex(x, ptr, "q", "", "=&r")
 #endif
 
 #define __get_user_size(x, ptr, size, retval, errret)			\
@@ -364,13 +364,13 @@ do {									\
 	__chk_user_ptr(ptr);						\
 	switch (size) {							\
 	case 1:								\
-		__get_user_asm_ex(x, ptr, "b", "b", "=q");		\
+		__get_user_asm_ex(x, ptr, "b", "b", "=&q");		\
 		break;							\
 	case 2:								\
-		__get_user_asm_ex(x, ptr, "w", "w", "=r");		\
+		__get_user_asm_ex(x, ptr, "w", "w", "=&r");		\
 		break;							\
 	case 4:								\
-		__get_user_asm_ex(x, ptr, "l", "k", "=r");		\
+		__get_user_asm_ex(x, ptr, "l", "k", "=&r");		\
 		break;							\
 	case 8:								\
 		__get_user_asm_ex_u64(x, ptr);				\
@@ -384,7 +384,7 @@ do {									\
 	asm volatile("1:	mov"itype" %1,%"rtype"0\n"		\
 		     "2:\n"						\
 		     _ASM_EXTABLE_EX(1b, 2b)				\
-		     : ltype(x) : "m" (__m(addr)))
+		     : ltype(x) : "m" (__m(addr)), "0" (0))
 
 #define __put_user_nocheck(x, ptr, size)			\
 ({								\