linux-kernel - Re: [PATCH v16 05/16] arm64: untag user pointers passed to memory syscalls

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Message-ID: <20190611174448.exg2zycfqf4a2vea@mbp>
Date:   Tue, 11 Jun 2019 18:44:48 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     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>,
        Kees Cook <keescook@...omium.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>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        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>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v16 05/16] arm64: untag user pointers passed to memory
 syscalls

On Tue, Jun 11, 2019 at 05:35:31PM +0200, Andrey Konovalov wrote:
> On Mon, Jun 10, 2019 at 4:28 PM Catalin Marinas <catalin.marinas@....com> wrote:
> > On Mon, Jun 03, 2019 at 06:55:07PM +0200, Andrey Konovalov wrote:
> > > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > > pass tagged user pointers (with the top byte set to something else other
> > > than 0x00) as syscall arguments.
> > >
> > > This patch allows tagged pointers to be passed to the following memory
> > > syscalls: get_mempolicy, madvise, mbind, mincore, mlock, mlock2, mprotect,
> > > mremap, msync, munlock.
> > >
> > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> >
> > I would add in the commit log (and possibly in the code with a comment)
> > that mremap() and mmap() do not currently accept tagged hint addresses.
> > Architectures may interpret the hint tag as a background colour for the
> > corresponding vma. With this:
> 
> I'll change the commit log. Where do you you think I should put this
> comment? Before mmap and mremap definitions in mm/?

On arm64 we use our own sys_mmap(). I'd say just add a comment on the
generic mremap() just before the untagged_addr() along the lines that
new_address is not untagged for preserving similar behaviour to mmap().

-- 
Catalin