linux-kernel - Re: [PATCH 4/5] kmsan: enter the runtime around kmsan_internal_memmove

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Message-ID: <CANpmjNO6aSwyvsnfcLs1fd8vBET+VaVx2=AX6WcVGJ1tZqcv7A@mail.gmail.com>
Date: Wed, 7 May 2025 18:09:44 +0200
From: Marco Elver <elver@...gle.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: dvyukov@...gle.com, bvanassche@....org, kent.overstreet@...ux.dev, 
	iii@...ux.ibm.com, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, 
	kasan-dev@...glegroups.com
Subject: Re: [PATCH 4/5] kmsan: enter the runtime around kmsan_internal_memmove_metadata()
 call

On Wed, 7 May 2025 at 18:00, Alexander Potapenko <glider@...gle.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@...gle.com>
> Cc: Bart Van Assche <bvanassche@....org>
> Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> Signed-off-by: Alexander Potapenko <glider@...gle.com>

Acked-by: Marco Elver <elver@...gle.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
>