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

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Date:   Fri, 1 Mar 2019 10:37:04 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Cc:     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 3/1/19 8:59 AM, Catalin Marinas wrote:
>>> 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().

If that's truly the common case, sounds like we should have a find_vma()
that does the vma_end checking as well.  Then at least the common case
would not have to worry about tagging.