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References: <cover.1544099024.git.andreyknvl@google.com> <bda78069e3b8422039794050ddcb2d53d053ed41.1544099024.git.andreyknvl@google.com>
 <2bf7415e-2724-b3c3-9571-20c8b6d43b92@arm.com>
In-Reply-To: <2bf7415e-2724-b3c3-9571-20c8b6d43b92@arm.com>
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
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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>, 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 <kasan-dev@googlegroups.com>, "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-sparse@vger.kernel.org, Linux Memory Management List <linux-mm@kvack.org>, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, 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>, Evgenii Stepanov <eugenis@google.com>

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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