linux-kernel - Re: [PATCH v19 00/15] arm64: untag user pointers passed to the kernel

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Message-ID: <20190724140212.qzvbcx5j2gi5lcoj@willie-the-truck>
Date:   Wed, 24 Jul 2019 15:02:12 +0100
From:   Will Deacon <will@...nel.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>, kvm@...r.kernel.org,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        Will Deacon <will.deacon@....com>,
        dri-devel@...ts.freedesktop.org,
        Kostya Serebryany <kcc@...gle.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Leon Romanovsky <leon@...nel.org>, linux-rdma@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org,
        Christoph Hellwig <hch@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
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        Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Subject: Re: [PATCH v19 00/15] arm64: untag user pointers passed to the kernel

Hi Andrey,

On Tue, Jul 23, 2019 at 08:03:29PM +0200, Andrey Konovalov wrote:
> On Tue, Jul 23, 2019 at 7:59 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
> >
> > === Overview
> >
> > arm64 has a feature called Top Byte Ignore, which allows to embed pointer
> > tags into the top byte of each pointer. Userspace programs (such as
> > HWASan, a memory debugging tool [1]) might use this feature and pass
> > tagged user pointers to the kernel through syscalls or other interfaces.
> >
> > Right now the kernel is already able to handle user faults with tagged
> > pointers, due to these patches:
> >
> > 1. 81cddd65 ("arm64: traps: fix userspace cache maintenance emulation on a
> >              tagged pointer")
> > 2. 7dcd9dd8 ("arm64: hw_breakpoint: fix watchpoint matching for tagged
> >               pointers")
> > 3. 276e9327 ("arm64: entry: improve data abort handling of tagged
> >               pointers")
> >
> > This patchset extends tagged pointer support to syscall arguments.

[...]

> Do you think this is ready to be merged?
> 
> Should this go through the mm or the arm tree?

I would certainly prefer to take at least the arm64 bits via the arm64 tree
(i.e. patches 1, 2 and 15). We also need a Documentation patch describing
the new ABI.

Will