Re: [PATCH] kasan: Fix hw tags enablement when KUNIT tests are disabled

[Andrey Konovalov]

On Fri, Apr 8, 2022 at 12:04 PM Vincenzo Frascino
<vincenzo.frascino@xxxxxxx> wrote:
>
> Kasan enables hw tags via kasan_enable_tagging() which based on the mode
> passed via kernel command line selects the correct hw backend.
> kasan_enable_tagging() is meant to be invoked indirectly via the cpu features
> framework of the architectures that support these backends.
> Currently the invocation of this function is guarded by CONFIG_KASAN_KUNIT_TEST
> which allows the enablement of the correct backend only when KUNIT tests are
> enabled in the kernel.

> ... and prevents to enable MTE on arm64 when KUNIT tests for kasan hw_tags are
> disabled.

Oh, indeed. Thanks for finding this!

> This inconsistency was introduced in commit:
>
>   f05842cfb9ae2 ("kasan, arm64: allow using KUnit tests with HW_TAGS mode")

No, that commit is fine. The issue was introduced recently in
ed6d74446cbf ("kasan: test: support async (again) and asymm modes for
HW_TAGS"), where I changed kasan_init_hw_tags_cpu() to call
kasan_enable_tagging() instead of hw_enable_tagging_*().

> Fix the issue making sure that the CONFIG_KASAN_KUNIT_TEST guard does not
> prevent the correct invocation of kasan_enable_tagging().
>
> Fixes: f05842cfb9ae2 ("kasan, arm64: allow using KUnit tests with HW_TAGS mode")
> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> ---
>  mm/kasan/hw_tags.c |  4 ++--
>  mm/kasan/kasan.h   | 10 ++++++----
>  2 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 07a76c46daa5..e2677501c36e 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -336,8 +336,6 @@ void __kasan_poison_vmalloc(const void *start, unsigned long size)
>
>  #endif
>
> -#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
> -
>  void kasan_enable_tagging(void)
>  {
>         if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
> @@ -349,6 +347,8 @@ void kasan_enable_tagging(void)
>  }
>  EXPORT_SYMBOL_GPL(kasan_enable_tagging);

Please keep this EXPORT_SYMBOL_GPL under CONFIG_KASAN_KUNIT_TEST.

>
> +#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
> +
>  void kasan_force_async_fault(void)
>  {
>         hw_force_async_tag_fault();
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index d79b83d673b1..b01b4bbe0409 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -355,25 +355,27 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>  #define hw_set_mem_tag_range(addr, size, tag, init) \
>                         arch_set_mem_tag_range((addr), (size), (tag), (init))
>
> +void kasan_enable_tagging(void);
> +
>  #else /* CONFIG_KASAN_HW_TAGS */
>
>  #define hw_enable_tagging_sync()
>  #define hw_enable_tagging_async()
>  #define hw_enable_tagging_asymm()
>
> +static inline void kasan_enable_tagging(void) { }
> +
>  #endif /* CONFIG_KASAN_HW_TAGS */
>
>  #if defined(CONFIG_KASAN_HW_TAGS) && IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
>
> -void kasan_enable_tagging(void);
>  void kasan_force_async_fault(void);
>
> -#else /* CONFIG_KASAN_HW_TAGS || CONFIG_KASAN_KUNIT_TEST */
> +#else /* CONFIG_KASAN_HW_TAGS && CONFIG_KASAN_KUNIT_TEST */
>
> -static inline void kasan_enable_tagging(void) { }
>  static inline void kasan_force_async_fault(void) { }
>
> -#endif /* CONFIG_KASAN_HW_TAGS || CONFIG_KASAN_KUNIT_TEST */
> +#endif /* CONFIG_KASAN_HW_TAGS && CONFIG_KASAN_KUNIT_TEST */
>
>  #ifdef CONFIG_KASAN_SW_TAGS
>  u8 kasan_random_tag(void);
> --
> 2.35.1
>

Thank you, Vincenzo!