linux-kernel - Re: [PATCH v14 10/17] fs, arm64: untag user pointers in fs/userfaultfd.c

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Date:   Mon, 6 May 2019 16:15:20 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....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>, Kuehling@...gle.com,
        Felix <Felix.Kuehling@....com>, Deucher@...gle.com,
        Alexander <Alexander.Deucher@....com>, Koenig@...gle.com,
        Christian <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>,
        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>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v14 10/17] fs, arm64: untag user pointers in fs/userfaultfd.c

On Fri, May 3, 2019 at 6:56 PM Catalin Marinas <catalin.marinas@....com> wrote:
>
> On Tue, Apr 30, 2019 at 03:25:06PM +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.
> >
> > userfaultfd_register() and userfaultfd_unregister() use provided user
> > pointers for vma lookups, which can only by done with untagged pointers.
> >
> > Untag user pointers in these functions.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > ---
> >  fs/userfaultfd.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > index f5de1e726356..fdee0db0e847 100644
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -1325,6 +1325,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> >               goto out;
> >       }
> >
> > +     uffdio_register.range.start =
> > +             untagged_addr(uffdio_register.range.start);
> > +
> >       ret = validate_range(mm, uffdio_register.range.start,
> >                            uffdio_register.range.len);
> >       if (ret)
> > @@ -1514,6 +1517,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> >       if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
> >               goto out;
> >
> > +     uffdio_unregister.start = untagged_addr(uffdio_unregister.start);
> > +
> >       ret = validate_range(mm, uffdio_unregister.start,
> >                            uffdio_unregister.len);
> >       if (ret)
>
> Wouldn't it be easier to do this in validate_range()? There are a few
> more calls in this file, though I didn't check whether a tagged address
> would cause issues.

Yes, I think it makes more sense, will do in v15, thanks!

>
> --
> Catalin