From: Andy Lutomirski <luto@kernel.org>
Date: Fri, 22 Feb 2019 17:17:04 -0800
Subject: x86/uaccess: Don't leak the AC flag into __put_user() value evaluation
Git-commit: 2a418cf3f5f1caf911af288e978d61c9844b0695
Patch-mainline: v5.0
References: bsc#1114279
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
---
arch/x86/include/asm/uaccess.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -287,8 +287,7 @@ do { \
__put_user_asm(x, ptr, retval, "l", "k", "ir", errret); \
break; \
case 8: \
- __put_user_asm_u64((__typeof__(*ptr))(x), ptr, retval, \
- errret); \
+ __put_user_asm_u64(x, ptr, retval, errret); \
break; \
default: \
__put_user_bad(); \
@@ -434,8 +433,10 @@ do { \
#define __put_user_nocheck(x, ptr, size) \
({ \
int __pu_err; \
+ __typeof__(*(ptr)) __pu_val; \
+ __pu_val = x; \
__uaccess_begin(); \
- __put_user_size((x), (ptr), (size), __pu_err, -EFAULT); \
+ __put_user_size(__pu_val, (ptr), (size), __pu_err, -EFAULT); \
__uaccess_end(); \
__builtin_expect(__pu_err, 0); \
})