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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Wed, 12 Dec 2018 16:04:20 +0100
Message-ID: <CAAeHK+xc6R_p26-tu--9W1L1PvUAFb70J23ByiEukKz3uVC3EQ@mail.gmail.com>
Subject: Re: [PATCH v13 19/25] kasan: add hooks implementation for tag-based mode
To:     Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc:     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>,
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        Arnd Bergmann <arnd@arndb.de>,
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On Tue, Dec 11, 2018 at 5:22 PM Vincenzo Frascino
<vincenzo.frascino@arm.com> wrote:
>
> 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?

I didn't know about this macro. Looks like we can use it to do the
same thing. Do you think it's a better solution to redefine
ARCH_SLAB_MINALIGN to KASAN_SHADOW_SCALE_SIZE for arm64 when tag-based
KASAN is enabled instead of adjusting cache->align in
kasan_cache_create?

>
> --
> Regards,
> Vincenzo
>
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