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

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Message-ID: <20190530171540.GD35418@arrakis.emea.arm.com>
Date:   Thu, 30 May 2019 18:15:40 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Evgenii Stepanov <eugenis@...gle.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>,
        Elliott Hughes <enh@...gle.com>,
        Khalid Aziz <khalid.aziz@...cle.com>
Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel

On Tue, May 28, 2019 at 04:14:45PM +0200, Andrey Konovalov wrote:
> Thanks for a lot of valuable input! I've read through all the replies
> and got somewhat lost. What are the changes I need to do to this
> series?
> 
> 1. Should I move untagging for memory syscalls back to the generic
> code so other arches would make use of it as well, or should I keep
> the arm64 specific memory syscalls wrappers and address the comments
> on that patch?

Keep them generic again but make sure we get agreement with Khalid on
the actual ABI implications for sparc.

> 2. Should I make untagging opt-in and controlled by a command line argument?

Opt-in, yes, but per task rather than kernel command line option.
prctl() is a possibility of opting in.

> 3. Should I "add Documentation/core-api/user-addresses.rst to describe
> proper care and handling of user space pointers with untagged_addr(),
> with examples based on all the cases seen so far in this series"?
> Which examples specifically should it cover?

I think we can leave 3 for now as not too urgent. What I'd like is for
Vincenzo's TBI user ABI document to go into a more common place since we
can expand it to cover both sparc and arm64. We'd need an arm64-specific
doc as well for things like prctl() and later MTE that sparc may support
differently.

-- 
Catalin