linux-kernel - Re: [PATCH v8 0/8] arm64: untag user pointers passed to the kernel

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Date:   Thu, 6 Dec 2018 13:44:24 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        Kostya Serebryany <kcc@...gle.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Lee Smith <Lee.Smith@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v8 0/8] arm64: untag user pointers passed to the kernel

On Thu, Nov 29, 2018 at 7:16 PM Catalin Marinas <catalin.marinas@....com> wrote:
>
> Hi Andrey,
>
> On Thu, Nov 08, 2018 at 03:48:10PM +0100, Andrey Konovalov wrote:
> > On Thu, Nov 8, 2018 at 3:36 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> > > Changes in v8:
> > > - Rebased onto 65102238 (4.20-rc1).
> > > - Added a note to the cover letter on why syscall wrappers/shims that untag
> > >   user pointers won't work.
> > > - Added a note to the cover letter that this patchset has been merged into
> > >   the Pixel 2 kernel tree.
> > > - Documentation fixes, in particular added a list of syscalls that don't
> > >   support tagged user pointers.
> >
> > I've changed the documentation to be more specific, please take a look.
> >
> > I haven't done anything about adding a way for the user to find out
> > that the kernel supports this ABI extension. I don't know what would
> > the the preferred way to do this, and we haven't received any comments
> > on that from anybody else. Probing "on some innocuous syscall
> > currently returning -EFAULT on tagged pointer arguments" works though,
> > as you mentioned.
>
> We've had some internal discussions and also talked to some people at
> Plumbers. I think the best option is to introduce an AT_FLAGS bit to
> describe the ABI relaxation on tagged pointers. Vincenzo is going to
> propose a patch on top of this series.

So should I wait for a patch from Vincenzo before posting v9 or post
it as is? Or try to develop this patch myself?

>
> > As mentioned in the cover letter, this patchset has been merged into
> > the Pixel 2 kernel tree.
>
> I just hope it's not enabled on production kernels, it would introduce
> a user ABI that may differ from what ends up upstream.
>
> --
> Catalin