Re: [PATCH 4/5] kmsan: enter the runtime around kmsan_internal_memmove_metadata() call

Marco Elver
2025-05-07T16:10:21Z

On Wed, 7 May 2025 at 18:00, Alexander Potapenko <glider@google.com> wrote:
>
> kmsan_internal_memmove_metadata() transitively calls stack_depot_save()
> (via kmsan_internal_chain_origin() and kmsan_save_stack_with_flags()),
> which may allocate memory. Guard it with kmsan_enter_runtime() and
> kmsan_leave_runtime() to avoid recursion.
>
> This bug was spotted by CONFIG_WARN_CAPABILITY_ANALYSIS=y
>
> Cc: Marco Elver <elver@google.com>
> Cc: Bart Van Assche <bvanassche@acm.org>
> Cc: Kent Overstreet <kent.overstreet@linux.dev>
> Signed-off-by: Alexander Potapenko <glider@google.com>

Acked-by: Marco Elver <elver@google.com>

> ---
> mm/kmsan/hooks.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
> index 05f2faa540545..97de3d6194f07 100644
> --- a/mm/kmsan/hooks.c
> +++ b/mm/kmsan/hooks.c
> @@ -275,8 +275,10 @@ void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
> * Don't check anything, just copy the shadow of the copied
> * bytes.
> */
> + kmsan_enter_runtime();
> kmsan_internal_memmove_metadata((void *)to, (void *)from,
> to_copy - left);
> + kmsan_leave_runtime();
> }
> user_access_restore(ua_flags);
> }
> --
> 2.49.0.967.g6a0df3ecc3-goog
>