linux-kernel - Re: [PATCH v4 00/17] khwasan: kernel hardware assisted address sanitizer

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Message-ID: <CAAeHK+zwmOMgP=Om6TKz8V5_4qgFhDfQSA01CBMnhbBWmHe9sQ@mail.gmail.com>
Date:   Fri, 29 Jun 2018 16:40:20 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christoph Lameter <cl@...ux.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Dave Martin <dave.martin@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-sparse@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Jann Horn <jannh@...gle.com>,
        Mark Brand <markbrand@...gle.com>,
        Chintan Pandya <cpandya@...eaurora.org>
Subject: Re: [PATCH v4 00/17] khwasan: kernel hardware assisted address sanitizer

On Fri, Jun 29, 2018 at 3:01 PM, Mark Rutland <mark.rutland@....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.