Re: [PATCH v2] kasan: add kasan mode messages when kasan init

[Marco Elver <elver@google.com>]

On Wed, 20 Oct 2021 at 08:13, Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com> wrote:
>
> There are multiple kasan modes. It makes sense that we add some messages
> to know which kasan mode is when booting up. see [1].
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=212195 [1]
> Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
> ---
> change since v2:
>  - Rebase to linux-next
>  - HW-tags based mode need to consider asymm mode
>  - Thanks for Marco's suggestion
>
>  arch/arm64/mm/kasan_init.c |  2 +-
>  mm/kasan/hw_tags.c         |  4 +++-
>  mm/kasan/kasan.h           | 10 ++++++++++
>  mm/kasan/sw_tags.c         |  2 +-
>  4 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index 5b996ca4d996..6f5a6fe8edd7 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -309,7 +309,7 @@ void __init kasan_init(void)
>         kasan_init_depth();
>  #if defined(CONFIG_KASAN_GENERIC)
>         /* CONFIG_KASAN_SW_TAGS also requires kasan_init_sw_tags(). */
> -       pr_info("KernelAddressSanitizer initialized\n");
> +       pr_info("KernelAddressSanitizer initialized (generic)\n");
>  #endif
>  }
>
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index dc892119e88f..1d5c89c7cdfe 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -177,7 +177,9 @@ void __init kasan_init_hw_tags(void)
>                 break;
>         }
>
> -       pr_info("KernelAddressSanitizer initialized\n");
> +       pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, stacktrace=%s)\n",
> +               kasan_mode_info(),
> +               kasan_stack_collection_enabled() ? "on" : "off");
>  }
>
>  void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index aebd8df86a1f..387ed7b6de37 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -36,6 +36,16 @@ static inline bool kasan_sync_fault_possible(void)
>  {
>         return kasan_mode == KASAN_MODE_SYNC || kasan_mode == KASAN_MODE_ASYMM;
>  }
> +
> +static inline const char *kasan_mode_info(void)
> +{
> +       if (kasan_mode == KASAN_MODE_ASYNC)
> +               return "async";
> +       else if (kasan_mode == KASAN_MODE_ASYMM)
> +               return "asymm";
> +       else
> +               return "sync";
> +}

This creates an inconsistency, because for
kasan_stack_collection_enabled(), kasan_async_fault_possible(), and
kasan_sync_fault_possible() there are !KASAN_HW_TAGS stubs.

A stub for kasan_mode_info() if !KASAN_HW_TAGS appears useless though,
and I wouldn't know what its return value should be.

Do you expect this helper to be used outside hw_tags.c? If not,
perhaps just move it into hw_tags.c.

Thanks,
-- Marco