On Thu, Oct 22, 2020 at 1:45 PM Marco Elver <el...@google.com> wrote:
>
> Avoid setting up watchpoints on NULL pointers, as otherwise we would
> crash inside the KCSAN runtime (when checking for value changes) instead
> of the instrumented code.
>
> Because that may be confusing, skip any address less than PAGE_SIZE.
>
> Signed-off-by: Marco Elver <el...@google.com>
Reviewed-by: Dmitry Vyukov <dvyu...@google.com>
> ---
> kernel/kcsan/encoding.h | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kcsan/encoding.h b/kernel/kcsan/encoding.h
> index f03562aaf2eb..64b3c0f2a685 100644
> --- a/kernel/kcsan/encoding.h
> +++ b/kernel/kcsan/encoding.h
> @@ -48,7 +48,11 @@
>
> static inline bool check_encodable(unsigned long addr, size_t size)
> {
> - return size <= MAX_ENCODABLE_SIZE;
> + /*
> + * While we can encode addrs<PAGE_SIZE, avoid crashing with a NULL
> + * pointer deref inside KCSAN.
> + */
> + return addr >= PAGE_SIZE && size <= MAX_ENCODABLE_SIZE;
> }
>
> static inline long
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>
