[PATCH 4.9 126/223] compiler.h: Add read_word_at_a_time() function.

Greg Kroah-Hartman
2019-08-02T09:45:42Z

[ Upstream commit 7f1e541fc8d57a143dd5df1d0a1276046e08c083 ]

Sometimes we know that it's safe to do potentially out-of-bounds access
because we know it won't cross a page boundary. Still, KASAN will
report this as a bug.

Add read_word_at_a_time() function which is supposed to be used in such
cases. In read_word_at_a_time() KASAN performs relaxed check - only the
first byte of access is validated.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/compiler.h | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index ced454c03819..3050de0dac96 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -302,6 +302,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
* with an explicit memory barrier or atomic instruction that provides the
* required ordering.
*/
+#include <linux/kasan-checks.h>

#define __READ_ONCE(x, check) \
({ \
@@ -320,6 +321,13 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
*/
#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)

+static __no_kasan_or_inline
+unsigned long read_word_at_a_time(const void *addr)
+{
+ kasan_check_read(addr, 1);
+ return *(unsigned long *)addr;
+}
+
#define WRITE_ONCE(x, val) \
({ \
union { typeof(x) __val; char __c[1]; } __u = \
--
2.20.1