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Subject: Re: [PATCH v13 19/25] kasan: add hooks implementation for tag-based
 mode
To:     Andrey Konovalov <andreyknvl@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Christoph Lameter <cl@linux.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Dave Martin <dave.martin@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Ingo Molnar <mingo@kernel.org>,
        Paul Lawrence <paullawrence@google.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        kasan-dev@googlegroups.com, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-sparse@vger.kernel.org, linux-mm@kvack.org,
        linux-kbuild@vger.kernel.org
Cc:     Vishwath Mohan <vishwath@google.com>,
        Chintan Pandya <cpandya@codeaurora.org>,
        Jacob Bramley <Jacob.Bramley@arm.com>,
        Jann Horn <jannh@google.com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
        Lee Smith <Lee.Smith@arm.com>,
        Kostya Serebryany <kcc@google.com>,
        Mark Brand <markbrand@google.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
        Evgeniy Stepanov <eugenis@google.com>
References: <cover.1544099024.git.andreyknvl@google.com>
 <bda78069e3b8422039794050ddcb2d53d053ed41.1544099024.git.andreyknvl@google.com>
From:   Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-ID: <2bf7415e-2724-b3c3-9571-20c8b6d43b92@arm.com>
Date:   Tue, 11 Dec 2018 16:22:43 +0000
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Hi Andrey,

On 06/12/2018 12:24, Andrey Konovalov wrote:
> This commit adds tag-based KASAN specific hooks implementation and
> adjusts common generic and tag-based KASAN ones.
> 
> 1. When a new slab cache is created, tag-based KASAN rounds up the size of
>    the objects in this cache to KASAN_SHADOW_SCALE_SIZE (== 16).
> 
> 2. On each kmalloc tag-based KASAN generates a random tag, sets the shadow
>    memory, that corresponds to this object to this tag, and embeds this
>    tag value into the top byte of the returned pointer.
> 
> 3. On each kfree tag-based KASAN poisons the shadow memory with a random
>    tag to allow detection of use-after-free bugs.
> 
> The rest of the logic of the hook implementation is very much similar to
> the one provided by generic KASAN. Tag-based KASAN saves allocation and
> free stack metadata to the slab object the same way generic KASAN does.
> 
> Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  mm/kasan/common.c | 116 ++++++++++++++++++++++++++++++++++++++--------
>  mm/kasan/kasan.h  |   8 ++++
>  mm/kasan/tags.c   |  48 +++++++++++++++++++
>  3 files changed, 153 insertions(+), 19 deletions(-)
>


[...]

> @@ -265,6 +290,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
>  		return;
>  	}
>  
> +	cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE);
> +

Did you consider to set ARCH_SLAB_MINALIGN instead of this round up?

-- 
Regards,
Vincenzo