Re: [PATCH v2 1/3] mm: kmsan: implement kmsan_memmove()

[Marco Elver <elver@google.com>]

On Wed, 20 Mar 2024 at 11:18, Alexander Potapenko <glider@google.com> wrote:
>
> Provide a hook that can be used by custom memcpy implementations to tell
> KMSAN that the metadata needs to be copied. Without that, false positive
> reports are possible in the cases where KMSAN fails to intercept memory
> initialization.
>
> Link: https://lore.kernel.org/all/3b7dbd88-0861-4638-b2d2-911c97a4cadf@I-love.SAKURA.ne.jp/
> Suggested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Marco Elver <elver@google.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>

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

> ---
>  include/linux/kmsan-checks.h | 15 +++++++++++++++
>  mm/kmsan/hooks.c             | 11 +++++++++++
>  2 files changed, 26 insertions(+)
>
> diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
> index c4cae333deec5..e1082dc40abc2 100644
> --- a/include/linux/kmsan-checks.h
> +++ b/include/linux/kmsan-checks.h
> @@ -61,6 +61,17 @@ void kmsan_check_memory(const void *address, size_t size);
>  void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
>                         size_t left);
>
> +/**
> + * kmsan_memmove() - Notify KMSAN about a data copy within kernel.
> + * @to:   destination address in the kernel.
> + * @from: source address in the kernel.
> + * @size: number of bytes to copy.
> + *
> + * Invoked after non-instrumented version (e.g. implemented using assembly
> + * code) of memmove()/memcpy() is called, in order to copy KMSAN's metadata.
> + */
> +void kmsan_memmove(void *to, const void *from, size_t to_copy);
> +
>  #else
>
>  static inline void kmsan_poison_memory(const void *address, size_t size,
> @@ -78,6 +89,10 @@ static inline void kmsan_copy_to_user(void __user *to, const void *from,
>  {
>  }
>
> +static inline void kmsan_memmove(void *to, const void *from, size_t to_copy)
> +{
> +}
> +
>  #endif
>
>  #endif /* _LINUX_KMSAN_CHECKS_H */
> diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
> index 5d6e2dee5692a..364f778ee226d 100644
> --- a/mm/kmsan/hooks.c
> +++ b/mm/kmsan/hooks.c
> @@ -285,6 +285,17 @@ void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
>  }
>  EXPORT_SYMBOL(kmsan_copy_to_user);
>
> +void kmsan_memmove(void *to, const void *from, size_t size)
> +{
> +       if (!kmsan_enabled || kmsan_in_runtime())
> +               return;
> +
> +       kmsan_enter_runtime();
> +       kmsan_internal_memmove_metadata(to, (void *)from, size);
> +       kmsan_leave_runtime();
> +}
> +EXPORT_SYMBOL(kmsan_memmove);
> +
>  /* Helper function to check an URB. */
>  void kmsan_handle_urb(const struct urb *urb, bool is_out)
>  {
> --
> 2.44.0.291.gc1ea87d7ee-goog
>