linux-kernel - Re: [PATCH v16 08/16] fs, arm64: untag user pointers in copy_mount

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Message-ID: <CAAeHK+xCmc-x=Mvs8RC+xJOCw6AnEUgUzXXjjS3NJXeLwJkyqg@mail.gmail.com>
Date:   Wed, 12 Jun 2019 13:36:36 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Kees Cook <keescook@...omium.org>
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>,
        Catalin Marinas <catalin.marinas@....com>,
        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>,
        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 08/16] fs, arm64: untag user pointers in copy_mount_options

On Tue, Jun 11, 2019 at 4:38 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
>
> On Sat, Jun 8, 2019 at 6:02 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Mon, Jun 03, 2019 at 06:55:10PM +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.
> > >
> > > In copy_mount_options a user address is being subtracted from TASK_SIZE.
> > > If the address is lower than TASK_SIZE, the size is calculated to not
> > > allow the exact_copy_from_user() call to cross TASK_SIZE boundary.
> > > However if the address is tagged, then the size will be calculated
> > > incorrectly.
> > >
> > > Untag the address before subtracting.
> > >
> > > Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> >
> > One thing I just noticed in the commit titles... "arm64" is in the
> > prefix, but these are arch-indep areas. Should the ", arm64" be left
> > out?
> >
> > I would expect, instead:
> >
> >         fs/namespace: untag user pointers in copy_mount_options
>
> Hm, I've added the arm64 tag in all of the patches because they are
> related to changes in arm64 kernel ABI. I can remove it from all the
> patches that only touch common code if you think that it makes sense.

I'll keep the arm64 tags in commit titles for v17. Please reply
explicitly if you think I should remove them. Thanks! :)

>
> Thanks!
>
> >
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> >
> > -Kees
> >
> > > ---
> > >  fs/namespace.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/namespace.c b/fs/namespace.c
> > > index b26778bdc236..2e85712a19ed 100644
> > > --- a/fs/namespace.c
> > > +++ b/fs/namespace.c
> > > @@ -2993,7 +2993,7 @@ void *copy_mount_options(const void __user * data)
> > >        * the remainder of the page.
> > >        */
> > >       /* copy_from_user cannot cross TASK_SIZE ! */
> > > -     size = TASK_SIZE - (unsigned long)data;
> > > +     size = TASK_SIZE - (unsigned long)untagged_addr(data);
> > >       if (size > PAGE_SIZE)
> > >               size = PAGE_SIZE;
> > >
> > > --
> > > 2.22.0.rc1.311.g5d7573a151-goog
> > >
> >
> > --
> > Kees Cook