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From: Andrey Konovalov <andreyknvl@google.com>
Date: Fri, 29 Jun 2018 16:40:20 +0200
Message-ID: <CAAeHK+zwmOMgP=Om6TKz8V5_4qgFhDfQSA01CBMnhbBWmHe9sQ@mail.gmail.com>
Subject: Re: [PATCH v4 00/17] khwasan: kernel hardware assisted address sanitizer
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To: Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, 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>, 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>, 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>, Kostya Serebryany <kcc@google.com>, Evgeniy Stepanov <eugenis@google.com>, Lee Smith <Lee.Smith@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Jann Horn <jannh@google.com>, Mark Brand <markbrand@google.com>, Chintan Pandya <cpandya@codeaurora.org>

On Fri, Jun 29, 2018 at 3:01 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Fri, Jun 29, 2018 at 02:45:08PM +0200, Andrey Konovalov wrote:
>> So with clean kernel after boot we get 40 kb memory usage. With KASAN
>> it is ~120 kb, which is 200% overhead. With KHWASAN it's 50 kb, which
>> is 25% overhead. This should approximately scale to any amounts of
>> used slab memory. For example with 100 mb memory usage we would get
>> +200 mb for KASAN and +25 mb with KHWASAN. (And KASAN also requires
>> quarantine for better use-after-free detection). I can explicitly
>> mention the overhead in %s in the changelog.
>
> Could you elaborate on where that SLAB overhead comes from?
>
> IIUC that's not for the shadow itself (since it's allocated up-front and
> not accounted to SLAB), and that doesn't take into account the
> quarantine, so what's eating that space?

Redzones. KHWASAN doesn't need them since the next slab object is
marked with a different tag (with a high probability) and acts as a
redzone.