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Date:   Thu, 1 Oct 2020 19:41:02 +0200
From:   elver@google.com
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        kasan-dev@googlegroups.com,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Elena Petrova <lenaptr@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 12/39] kasan: hide invalid free check implementation
Message-ID: <20201001174102.GJ4162920@elver.google.com>
References: <cover.1600987622.git.andreyknvl@google.com>
 <c1cef2ae4f4c5640afc8aac4339d77d140d45304.1600987622.git.andreyknvl@google.com>
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On Fri, Sep 25, 2020 at 12:50AM +0200, Andrey Konovalov wrote:
> This is a preparatory commit for the upcoming addition of a new hardware
> tag-based (MTE-based) KASAN mode.
> 
> For software KASAN modes the check is based on the value in the shadow
> memory. Hardware tag-based KASAN won't be using shadow, so hide the
> implementation of the check in check_invalid_free().
> 
> Also simplify the code for software tag-based mode.
> 
> No functional changes for software modes.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

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

> ---
> Change-Id: I5fae9531c9fc948eb4d4e0c589744032fc5a0789
> ---
>  mm/kasan/common.c  | 19 +------------------
>  mm/kasan/generic.c |  7 +++++++
>  mm/kasan/kasan.h   |  2 ++
>  mm/kasan/sw_tags.c |  9 +++++++++
>  4 files changed, 19 insertions(+), 18 deletions(-)
> 
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 123abfb760d4..543e6bf2168f 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -272,25 +272,9 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
>  	return (void *)object;
>  }
>  
> -static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
> -{
> -	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> -		return shadow_byte < 0 ||
> -			shadow_byte >= KASAN_GRANULE_SIZE;
> -
> -	/* else CONFIG_KASAN_SW_TAGS: */
> -	if ((u8)shadow_byte == KASAN_TAG_INVALID)
> -		return true;
> -	if ((tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte))
> -		return true;
> -
> -	return false;
> -}
> -
>  static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
>  			      unsigned long ip, bool quarantine)
>  {
> -	s8 shadow_byte;
>  	u8 tag;
>  	void *tagged_object;
>  	unsigned long rounded_up_size;
> @@ -309,8 +293,7 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
>  	if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
>  		return false;
>  
> -	shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
> -	if (shadow_invalid(tag, shadow_byte)) {
> +	if (check_invalid_free(tagged_object)) {
>  		kasan_report_invalid_free(tagged_object, ip);
>  		return true;
>  	}
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index ec4417156943..e1af3b6c53b8 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -187,6 +187,13 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
>  	return check_memory_region_inline(addr, size, write, ret_ip);
>  }
>  
> +bool check_invalid_free(void *addr)
> +{
> +	s8 shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(addr));
> +
> +	return shadow_byte < 0 || shadow_byte >= KASAN_GRANULE_SIZE;
> +}
> +
>  void kasan_cache_shrink(struct kmem_cache *cache)
>  {
>  	quarantine_remove_cache(cache);
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 1865bb92d47a..3eff57e71ff5 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -164,6 +164,8 @@ void kasan_poison_memory(const void *address, size_t size, u8 value);
>  bool check_memory_region(unsigned long addr, size_t size, bool write,
>  				unsigned long ret_ip);
>  
> +bool check_invalid_free(void *addr);
> +
>  void *find_first_bad_addr(void *addr, size_t size);
>  const char *get_bug_type(struct kasan_access_info *info);
>  
> diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> index 4bdd7dbd6647..b2638c2cd58a 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -121,6 +121,15 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
>  	return true;
>  }
>  
> +bool check_invalid_free(void *addr)
> +{
> +	u8 tag = get_tag(addr);
> +	u8 shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(reset_tag(addr)));
> +
> +	return (shadow_byte == KASAN_TAG_INVALID) ||
> +		(tag != KASAN_TAG_KERNEL && tag != shadow_byte);
> +}
> +
>  #define DEFINE_HWASAN_LOAD_STORE(size)					\
>  	void __hwasan_load##size##_noabort(unsigned long addr)		\
>  	{								\
> -- 
> 2.28.0.681.g6f77f65b4e-goog
>