FAILED: patch "[PATCH] x86/uaccess: Don't leak the AC flag into __put_user() value" failed to apply to 4.14-stable tree

The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2a418cf3f5f1caf911af288e978d61c9844b0695 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <[email protected]>
Date: Fri, 22 Feb 2019 17:17:04 -0800
Subject: [PATCH] x86/uaccess: Don't leak the AC flag into __put_user() value
evaluation

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. ]

index a77445d1b034..28376aa2d053 100644
@@ -284,7 +284,7 @@ do {									\
 		__put_user_goto(x, ptr, "l", "k", "ir", label);		\
 		break;							\
 	case 8:								\
-		__put_user_goto_u64((__typeof__(*ptr))(x), ptr, label);	\
+		__put_user_goto_u64(x, ptr, label);			\
 		break;							\
 	default:							\
 		__put_user_bad();					\

@@ -431,8 +431,10 @@ do {									\
 ({								\
 	__label__ __pu_label;					\
 	int __pu_err = -EFAULT;					\
+	__typeof__(*(ptr)) __pu_val;				\
+	__pu_val = x;						\
 	__uaccess_begin();					\
-	__put_user_size((x), (ptr), (size), __pu_label);	\
+	__put_user_size(__pu_val, (ptr), (size), __pu_label);	\
 	__pu_err = 0;						\
 __pu_label:							\
 	__uaccess_end();					\