[PATCH 4.19 69/79] x86/uaccess: Dont leak the AC flags into __get_user() argument evaluation

Greg Kroah-Hartman
2019-09-19T22:14:52Z

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit 9b8bd476e78e89c9ea26c3b435ad0201c3d7dbf5 ]

Identical to __put_user(); the __get_user() argument evalution will too
leak UBSAN crud into the __uaccess_begin() / __uaccess_end() region.
While uncommon this was observed to happen for:

drivers/xen/gntdev.c: if (__get_user(old_status, batch->status[i]))

where UBSAN added array bound checking.

This complements commit:

6ae865615fc4 ("x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation")

Tested-by Sedat Dilek <sedat.dilek@gmail.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: broonie@kernel.org
Cc: sfr@canb.auug.org.au
Cc: akpm@linux-foundation.org
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: mhocko@suse.cz
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20190829082445.GM2369@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/include/asm/uaccess.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 4111edb3188e2..9718303410614 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -451,8 +451,10 @@ do { \
({ \
int __gu_err; \
__inttype(*(ptr)) __gu_val; \
+ __typeof__(ptr) __gu_ptr = (ptr); \
+ __typeof__(size) __gu_size = (size); \
__uaccess_begin_nospec(); \
- __get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT); \
+ __get_user_size(__gu_val, __gu_ptr, __gu_size, __gu_err, -EFAULT); \
__uaccess_end(); \
(x) = (__force __typeof__(*(ptr)))__gu_val; \
__builtin_expect(__gu_err, 0); \
--
2.20.1