linux-kernel - Re: [PATCH v17 03/15] arm64: Introduce prctl() options to control the tagged user addresses ABI

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Date:   Tue, 18 Jun 2019 10:18:12 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>, kvm@...r.kernel.org,
        Christian Koenig <Christian.Koenig@....com>,
        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>,
        Lee Smith <Lee.Smith@....com>, linux-kselftest@...r.kernel.org,
        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>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        linux-media@...r.kernel.org,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felix Kuehling <Felix.Kuehling@....com>,
        linux-kernel@...r.kernel.org,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        enh <enh@...gle.com>, Robin Murphy <robin.murphy@....com>,
        Yishai Hadas <yishaih@...lanox.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Subject: Re: [PATCH v17 03/15] arm64: Introduce prctl() options to control
 the tagged user addresses ABI

On Thu, Jun 13, 2019 at 10:13:54PM -0700, Kees Cook wrote:
> On Thu, Jun 13, 2019 at 04:26:32PM +0100, Catalin Marinas wrote:
> > On Thu, Jun 13, 2019 at 12:02:35PM +0100, Dave P Martin wrote:
> > > On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote:
> > > > +static int zero;
> > > > +static int one = 1;
> > > 
> > > !!!
> > > 
> > > And these can't even be const without a cast.  Yuk.
> > > 
> > > (Not your fault though, but it would be nice to have a proc_dobool() to
> > > avoid this.)
> > 
> > I had the same reaction. Maybe for another patch sanitising this pattern
> > across the kernel.
> 
> That's actually already happening (via -mm tree last I looked). tl;dr:
> it ends up using a cast hidden in a macro. It's in linux-next already
> along with a checkpatch.pl addition to yell about doing what's being
> done here. ;)
> 
> https://lore.kernel.org/lkml/20190430180111.10688-1-mcroce@redhat.com/#r

Hmmm, that is marginally less bad.

Ideally we'd have a union in there, not just a bunch of void *.  I may
look at that someday...

Cheers
---Dave