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

Dmitry Vyukov
2019-02-27T15:40:43Z

On Wed, Feb 27, 2019 at 3:33 PM Peter Zijlstra <peterz@infradead.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).