linux-kernel - Re: [PATCH v2 08/20] kasan: inline random_tag for HW

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Date:   Wed, 11 Nov 2020 18:02:13 +0100
From:   Marco Elver <elver@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/20] kasan: inline random_tag for HW_TAGS

On Tue, Nov 10, 2020 at 11:20PM +0100, Andrey Konovalov wrote:
> Using random_tag() currently results in a function call. Move its
> definition to mm/kasan/kasan.h and turn it into a static inline function
> for hardware tag-based mode to avoid uneeded function calls.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> Link: https://linux-review.googlesource.com/id/Iac5b2faf9a912900e16cca6834d621f5d4abf427
> ---
>  mm/kasan/hw_tags.c |  5 -----
>  mm/kasan/kasan.h   | 34 +++++++++++++++++-----------------
>  2 files changed, 17 insertions(+), 22 deletions(-)

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

But see style comments below.

> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 49ea5f5c5643..1476ac07666e 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -42,11 +42,6 @@ void kasan_unpoison_memory(const void *address, size_t size)
>  			round_up(size, KASAN_GRANULE_SIZE), get_tag(address));
>  }
>  
> -u8 random_tag(void)
> -{
> -	return hw_get_random_tag();
> -}
> -
>  bool check_invalid_free(void *addr)
>  {
>  	u8 ptr_tag = get_tag(addr);
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 8a5501ef2339..7498839a15d3 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -188,6 +188,12 @@ static inline bool addr_has_metadata(const void *addr)
>  
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>  
> +#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
> +void print_tags(u8 addr_tag, const void *addr);
> +#else
> +static inline void print_tags(u8 addr_tag, const void *addr) { }
> +#endif
> +
>  bool check_invalid_free(void *addr);
>  
>  void *find_first_bad_addr(void *addr, size_t size);
> @@ -223,23 +229,6 @@ static inline void quarantine_reduce(void) { }
>  static inline void quarantine_remove_cache(struct kmem_cache *cache) { }
>  #endif
>  
> -#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
> -
> -void print_tags(u8 addr_tag, const void *addr);
> -
> -u8 random_tag(void);
> -
> -#else
> -
> -static inline void print_tags(u8 addr_tag, const void *addr) { }
> -
> -static inline u8 random_tag(void)
> -{
> -	return 0;
> -}
> -
> -#endif
> -
>  #ifndef arch_kasan_set_tag
>  static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>  {
> @@ -279,6 +268,17 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>  
>  #endif /* CONFIG_KASAN_HW_TAGS */
>  
> +#ifdef CONFIG_KASAN_SW_TAGS
> +u8 random_tag(void);
> +#elif defined(CONFIG_KASAN_HW_TAGS)
> +#define random_tag() hw_get_random_tag()

Shouldn't this also be a function?

+static inline u8 random_tag(void) { return hw_get_random_tag(); }

Or is there a reason why this was made a macro?

> +#else
> +static inline u8 random_tag(void)
> +{
> +	return 0;
> +}

Could just be on 1 line:

+static inline u8 random_tag(void) { return 0; }

> +#endif
> +
>  /*
>   * Exported functions for interfaces called from assembly or from generated
>   * code. Declarations here to avoid warning about missing declarations.
> -- 
> 2.29.2.222.g5d2a92d10f8-goog
>