linux-kernel - Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm

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Date:   Wed, 7 Dec 2016 13:57:40 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias

On Tue, Dec 06, 2016 at 12:10:50PM -0800, Kees Cook wrote:
> On Tue, Dec 6, 2016 at 10:18 AM, Mark Rutland <mark.rutland@....com> wrote:
> > On Tue, Nov 29, 2016 at 11:39:44AM -0800, Kees Cook wrote:
> >> On Tue, Nov 29, 2016 at 10:55 AM, Laura Abbott <labbott@...hat.com> wrote:
> >> >
> >> > The usercopy checking code currently calls __va(__pa(...)) to check for
> >> > aliases on symbols. Switch to using lm_alias instead.
> >> >
> >> > Signed-off-by: Laura Abbott <labbott@...hat.com>
> >>
> >> Acked-by: Kees Cook <keescook@...omium.org>
> >>
> >> I should probably add a corresponding alias test to lkdtm...
> >>
> >> -Kees
> >
> > Something like the below?
> >
> > It uses lm_alias(), so it depends on Laura's patches. We seem to do the
> > right thing, anyhow:
> 
> Cool, this looks good. What happens on systems without an alias?

In that case, lm_alias() should be an identity function, and we'll just
hit the usual kernel address (i.e. it should be identical to
USERCOPY_KERNEL).

> Laura, feel free to add this to your series:
> 
> Acked-by: Kees Cook <keescook@...omium.org>

I'm happy with that, or I can resend this as a proper patch once the
rest is in.

Thanks,
Mark.