On Wed, Mar 25, 2020 at 5:13 PM <glider@xxxxxxxxxx> wrote:
>
> READ_ONCE_NOCHECK() is already used by KASAN to ignore memory accesses
> from e.g. stack unwinders.
> Define READ_ONCE_NOCHECK() for KMSAN so that it returns initialized
> values. This helps defeat false positives from leftover stack contents.
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> To: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
> v3:
> - removed unnecessary #ifdef as requested by Mark Rutland
> v4:
> - added an #include as requested by Marco Elver
>
> Change-Id: Ib38369ba038ab3b581d8e45b81036c3304fb79cb
> ---
> include/linux/compiler.h | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index f504edebd5d71..c6c67729729e3 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -279,6 +279,7 @@ void __write_once_size(volatile void *p, void *res, int size)
> */
> #include <asm/barrier.h>
> #include <linux/kasan-checks.h>
> +#include <linux/kmsan-checks.h>
>
> #define __READ_ONCE(x, check) \
> ({ \
> @@ -294,9 +295,9 @@ void __write_once_size(volatile void *p, void *res, int size)
>
> /*
> * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
> - * to hide memory access from KASAN.
> + * to hide memory access from KASAN or KMSAN.
> */
> -#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
> +#define READ_ONCE_NOCHECK(x) KMSAN_INIT_VALUE(__READ_ONCE(x, 0))
>
> static __no_kasan_or_inline
> unsigned long read_word_at_a_time(const void *addr)
> --
> 2.25.1.696.g5e7596f4ac-goog
>
