[PATCH v2 3/9] kasan: sw_tags: Support outline stack tag generation

[Andrey Konovalov]

On Tue, Oct 22, 2024 at 3:59 AM Samuel Holland
<samuel.holland at sifive.com> wrote:
>
> 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.
>
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
> ---
>
> Changes in v2:
>  - Split the generic and RISC-V parts of stack tag generation control
>    to avoid breaking bisectability
>
>  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 f438a6cdc964..72da5ddcceaa 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 220b5d4c6876..32435d33583a 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -70,6 +70,15 @@ 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)
>  {
> --
> 2.45.1
>

Reviewed-by: Andrey Konovalov <andreyknvl at gmail.com>