Re: [PATCH v2 03/14] kasan: sw_tags: Support outline stack tag generation

[Andrey Konovalov]

On Tue, Feb 18, 2025 at 9:17 AM Maciej Wieczor-Retman
<maciej.wieczor-retman@xxxxxxxxx> wrote:
>
> From: Samuel Holland <samuel.holland@xxxxxxxxxx>
>
> This allows stack tagging to be disabled at runtime by tagging all
> stack objects with the match-all tag. This is necessary on RISC-V,
> where a kernel with KASAN_SW_TAGS enabled is expected to boot on
> hardware without pointer masking support.

Same question, is this needed on x86?



>
> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
> Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
> ---
>  mm/kasan/kasan.h   | 2 ++
>  mm/kasan/sw_tags.c | 9 +++++++++
>  2 files changed, 11 insertions(+)
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 129178be5e64..2fb26f74dff9 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -636,6 +636,8 @@ void *__asan_memset(void *addr, int c, ssize_t len);
>  void *__asan_memmove(void *dest, const void *src, ssize_t len);
>  void *__asan_memcpy(void *dest, const void *src, ssize_t len);
>
> +u8 __hwasan_generate_tag(void);
> +
>  void __hwasan_load1_noabort(void *);
>  void __hwasan_store1_noabort(void *);
>  void __hwasan_load2_noabort(void *);
> diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> index b9382b5b6a37..94465a8a3640 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -71,6 +71,15 @@ u8 kasan_random_tag(void)
>         return (u8)(state % (KASAN_TAG_MAX + 1));
>  }
>
> +u8 __hwasan_generate_tag(void)
> +{
> +       if (!kasan_enabled())
> +               return KASAN_TAG_KERNEL;
> +
> +       return kasan_random_tag();
> +}
> +EXPORT_SYMBOL(__hwasan_generate_tag);
> +
>  bool kasan_check_range(const void *addr, size_t size, bool write,
>                         unsigned long ret_ip)
>  {
> --
> 2.47.1
>