linux-kernel - Re: [PATCH 5/6] objtool: Add UACCESS validation

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Date:   Wed, 27 Feb 2019 16:40:28 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>, valentin.schneider@....com,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH 5/6] objtool: Add UACCESS validation

On Wed, Feb 27, 2019 at 3:33 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Feb 27, 2019 at 03:26:23PM +0100, Peter Zijlstra wrote:
> > On Wed, Feb 27, 2019 at 05:17:58PM +0300, Andrey Ryabinin wrote:
> > >
> > >
> > > On 2/27/19 5:08 PM, Peter Zijlstra wrote:
> >
> > > > I can't actually find any definitions of those functions, so I can't
> > > > very well mark the safe, even if we wanted to.
> > > >
> > >
> > > They are macro-generated. Use 'git grep DEFINE_ASAN'
> >
> > Ah, indeed! I'll go have a look.
>
> Urgh, kasan_report() is definitely unsafe. Now, admitedly we should
> 'never' hit that, but it does leave us up a creek without a paddle.
>
> Not sure what to do here; best I can come up with atm. is kill SMAP on
> KASAN builds.

If SMAP detects additional bugs, then it would be pity to disable it
with KASAN (detect bugs in production but not during testing).

You mentioned that exception save/restore the UACCESS state. Is it
possible to do the same in kasan_report? At the very least we need to
survive report printing, what happens after that does not matter much
(we've corrupted memory by now anyway).