linux-kernel - Re: [PATCH v10 07/12] fs, arm64: untag user pointers in fs/userfaultfd.c

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Message-ID: <20190301165908.GA130541@arrakis.emea.arm.com>
Date:   Fri, 1 Mar 2019 16:59:08 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kees Cook <keescook@...omium.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.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>,
        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 v10 07/12] fs, arm64: untag user pointers in
 fs/userfaultfd.c

On Tue, Feb 26, 2019 at 03:39:08PM +0100, Andrey Konovalov wrote:
> On Sat, Feb 23, 2019 at 12:06 AM Dave Hansen <dave.hansen@...el.com> wrote:
> >
> > On 2/22/19 4:53 AM, Andrey Konovalov wrote:
> > > userfaultfd_register() and userfaultfd_unregister() use provided user
> > > pointers for vma lookups, which can only by done with untagged pointers.
> >
> > So, we have to patch all these sites before the tagged values get to the
> > point of hitting the vma lookup functions.  Dumb question: Why don't we
> > just patch the vma lookup functions themselves instead of all of these
> > callers?
> 
> That might be a working approach as well. We'll still need to fix up
> places where the vma fields are accessed directly. Catalin, what do
> you think?

Most callers of find_vma*() always follow it by a check of
vma->vma_start against some tagged address ('end' in the
userfaultfd_(un)register()) case. So it's not sufficient to untag it in
find_vma().

-- 
Catalin