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From: Evgenii Stepanov <eugenis@google.com>
Date: Fri, 16 Mar 2018 11:45:42 -0700
Message-ID: <CAFKCwrheE=uDnrS5sH585CgciLg-o7uUsp45TNmF10cuUUR2GA@mail.gmail.com>
Subject: Re: [RFC PATCH 09/14] khwasan: add hooks implementation
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To: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, Jonathan Corbet <corbet@lwn.net>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.com>, Christopher Li <sparse@chrisli.org>, Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, Masahiro Yamada <yamada.masahiro@socionext.com>, Michal Marek <michal.lkml@markovi.net>, Mark Rutland <mark.rutland@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Yury Norov <ynorov@caviumnetworks.com>, Nick Desaulniers <ndesaulniers@google.com>, Marc Zyngier <marc.zyngier@arm.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Kristina Martsenko <kristina.martsenko@arm.com>, Punit Agrawal <punit.agrawal@arm.com>, Dave Martin <Dave.Martin@arm.com>, James Morse <james.morse@arm.com>, Julien Thierry <julien.thierry@arm.com>, Michael Weiser <michael.weiser@gmx.de>, Steve Capper <steve.capper@arm.com>, Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Sandipan Das <sandipan@linux.vnet.ibm.com>, Paul Lawrence <paullawrence@google.com>, David Woodhouse <dwmw@amazon.co.uk>, Kees Cook <keescook@chromium.org>, Geert Uytterhoeven <geert@linux-m68k.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Arnd Bergmann <arnd@arndb.de>, 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-ext4@vger.kernel.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>, Lee Smith <Lee.Smith@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Kees Cook <keescook@google.com>, Jann Horn <jannh@google.com>, Mark Brand <markbrand@google.com>

On Fri, Mar 16, 2018 at 11:24 AM, Andrey Konovalov
<andreyknvl@google.com> wrote:
> On Fri, Mar 16, 2018 at 7:16 PM, Evgenii Stepanov <eugenis@google.com> wrote:
>> On Fri, Mar 16, 2018 at 11:09 AM, Andrey Konovalov
>> <andreyknvl@google.com> wrote:
>>> On Thu, Mar 15, 2018 at 5:52 PM, Andrey Ryabinin
>>>> Wouldn't be better to have some reserved tag value for invalid memory (redzones/free), so that
>>>> we catch access to such memory with 100% probability?
>>>
>>> We could do that. That would reduce the chance to detect a
>>> use-after-free though, since we're using fewer different tag values
>>> for the objects themselves. I don't have a strong opinion about which
>>> one is better though.
>
> Note: I misread the message and didn't notice the "/free" part there,
> so I was considering marking only redzones with a reserved tag value.
>
>>
>> hwasan does not need redzones.
>
> Right, by redzones in this case I meant the metadata that is stored
> right after the object (which includes alloc and free stack handles
> and perhaps some other allocator stuff).

Oh, I did not realize we have free (as in beer, not as in
use-after-free) redzones between allocations. Yes, reserving a color
sounds
like a good idea.

>
>> As for use-after-free, to catch it with
>> 100% probability one would need infinite memory for the quarantine. It
>> is possible to guarantee 100% detection of linear buffer overflow by
>> giving live adjacent chunks distinct tags.