Re: [PATCH v3] kasan: add kasan mode messages when kasan init

[Marco Elver <elver@google.com>]

On Wed, 20 Oct 2021 at 11:48, 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>

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

Thank you.

Because this is rebased on the changes in the arm64 tree, and also
touches arch/arm64, it probably has to go through the arm64 tree.

> ---
> v3:
>  - Rebase to linux-next
>  - Move kasan_mode_info() into hw_tags.c
> v2:
>  - Rebase to linux-next
>  - HW-tag based mode need to consider asymm mode
>  - Thanks Marco's suggestion
>
>  arch/arm64/mm/kasan_init.c |  2 +-
>  mm/kasan/hw_tags.c         | 14 +++++++++++++-
>  mm/kasan/sw_tags.c         |  2 +-
>  3 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
>  }

Note: Other architectures may want to update their message once they
support any one of the tags modes. But currently that's not yet the
case.

You could also consider leaving out the "(generic)" bit if it's the
generic mode to avoid adding this to all arch/**/kasan_init.c. Both is
fine with me. I leave it to you.

> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index dc892119e88f..7355cb534e4f 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -106,6 +106,16 @@ static int __init early_kasan_flag_stacktrace(char *arg)
>  }
>  early_param("kasan.stacktrace", early_kasan_flag_stacktrace);
>
> +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";
> +}
> +
>  /* kasan_init_hw_tags_cpu() is called for each CPU. */
>  void kasan_init_hw_tags_cpu(void)
>  {
> @@ -177,7 +187,9 @@ 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/sw_tags.c b/mm/kasan/sw_tags.c
> index bd3f540feb47..77f13f391b57 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -42,7 +42,7 @@ void __init kasan_init_sw_tags(void)
>         for_each_possible_cpu(cpu)
>                 per_cpu(prng_state, cpu) = (u32)get_cycles();
>
> -       pr_info("KernelAddressSanitizer initialized\n");
> +       pr_info("KernelAddressSanitizer initialized (sw-tags)\n");
>  }
>
>  /*
> --
> 2.18.0

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