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compiler.h: Add read_word_at_a_time() function.

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[ 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>
This commit is contained in:
Andrey Ryabinin 2018-02-01 21:00:49 +03:00 committed by Greg Kroah-Hartman
parent 229b670e66
commit 4b5d4bdfd1
1 changed files with 8 additions and 0 deletions
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8
include/linux/compiler.h
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@ -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 = \