linux-kernel - Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel

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Date:   Thu, 23 May 2019 16:08:14 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Kees Cook <keescook@...omium.org>
Cc:     enh <enh@...gle.com>, Evgenii Stepanov <eugenis@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-rdma@...r.kernel.org, linux-media@...r.kernel.org,
        kvm@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel

On Wed, May 22, 2019 at 12:21:27PM -0700, Kees Cook wrote:
> If a process wants to not tag, that's also up to the allocator where
> it can decide not to ask the kernel, and just not tag. Nothing breaks in
> userspace if a process is NOT tagging and untagged_addr() exists or is
> missing. This, I think, is the core way this doesn't trip over the
> golden rule: an old system image will run fine (because it's not
> tagging). A *new* system may encounter bugs with tagging because it's a
> new feature: this is The Way Of Things. But we don't break old userspace
> because old userspace isn't using tags.

With this series and hwasan binaries, at some point in the future they
will be considered "old userspace" and they do use pointer tags which
expect to be ignored by both the hardware and the kernel. MTE breaks
this assumption.

-- 
Catalin