[PATCH v4.4] x86/uaccess: Don't leak the AC flag into __put_user() value evaluation - Linux-stable-mirror

3 Mar 2019

From: Andy Lutomirski luto@kernel.org
commit 2a418cf3f5f1caf911af288e978d61c9844b0695 upstream.
When calling __put_user(foo(), ptr), the __put_user() macro would call
foo() in between __uaccess_begin() and __uaccess_end().  If that code
were buggy, then those bugs would be run without SMAP protection.
Fortunately, there seem to be few instances of the problem in the
kernel. Nevertheless, __put_user() should be fixed to avoid doing this.
Therefore, evaluate __put_user()'s argument before setting AC.
This issue was noticed when an objtool hack by Peter Zijlstra complained
about genregs_get() and I compared the assembly output to the C source.
[ bp: Massage commit message and fixed up whitespace. ]
Fixes: 11f1a4b9755f ("x86: reorganize SMAP handling in user space accesses")
Signed-off-by: Andy Lutomirski luto@kernel.org
Signed-off-by: Borislav Petkov bp@suse.de
Acked-by: Linus Torvalds torvalds@linux-foundation.org
Cc: Peter Zijlstra peterz@infradead.org
Cc: Brian Gerst brgerst@gmail.com
Cc: Josh Poimboeuf jpoimboe@redhat.com
Cc: Denys Vlasenko dvlasenk@redhat.com
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20190225125231.845656645@infradead.org
Signed-off-by: Maxim Zhukov mussitantesmortem@gmail.com
---
 arch/x86/include/asm/uaccess.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index d788b0cdc0ad..4f4a9fa61b8a 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -306,7 +306,7 @@ do {									\
    	__put_user_asm(x, ptr, retval, "l", "k", "ir", errret);	\
    	break;							\
    case 8:								\
-		__put_user_asm_u64((__typeof__(*ptr))(x), ptr, retval,	\
+		__put_user_asm_u64(x, ptr, retval,	\
    			   errret);				\
    	break;							\
    default:							\
@@ -410,7 +410,9 @@ do {									\
 #define __put_user_nocheck(x, ptr, size)			\
 ({								\
    int __pu_err;						\
-	__put_user_size((x), (ptr), (size), __pu_err, -EFAULT);	\
+	__typeof__(*(ptr)) __pu_val;				\
+	__pu_val = x;						\
+	__put_user_size(__pu_val, (ptr), (size), __pu_err, -EFAULT);	\
    __builtin_expect(__pu_err, 0);				\
 })
-- 
2.21.0


    