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From:   Kees Cook <keescook@chromium.org>
Date:   Wed, 9 Jan 2019 12:05:02 -0800
Message-ID: <CAGXu5jK1En85PMUgHbzHoO2U84FiNoJLPF0rUXeyPaoY6GXEEA@mail.gmail.com>
Subject: Re: [PATCH] lkdtm: Add a tests for NULL pointer dereference
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        PowerPC <linuxppc-dev@lists.ozlabs.org>
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On Wed, Jan 9, 2019 at 7:16 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Tue, Jan 8, 2019 at 10:31 PM Christophe Leroy
> <christophe.leroy@c-s.fr> wrote:
> >
> >
> >
> > Le 09/01/2019 =C3=A0 02:14, Kees Cook a =C3=A9crit :
> > > On Fri, Dec 14, 2018 at 7:26 AM Christophe Leroy
> > > <christophe.leroy@c-s.fr> wrote:
> > >>
> > >> Introduce lkdtm tests for NULL pointer dereference: check
> > >> access or exec at NULL address.
> > >
> > > Why is this not already covered by the existing tests? (Is there
> > > something special about NULL that is being missed?) I'd expect SMAP
> > > and SMEP to cover NULL as well.
> >
> > Most arches print a different message whether the faulty address is
> > above or under PAGE_SIZE. Below is exemple from x86:
> >
> >         pr_alert("BUG: unable to handle kernel %s at %px\n",
> >                  address < PAGE_SIZE ? "NULL pointer dereference" : "pa=
ging request",
> >                  (void *)address);
> >
> >
> > Until recently, the powerpc arch didn't do it. When I implemented it
> > (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/com=
mit/?id=3D49a502ea23bf9dec47f8f3c3960909ff409cd1bb),
> > I needed a way to test it and couldn't find an existing one, hence this
> > new LKDTM test.
> >
> > But maybe I missed something ?
>
> Okay, gotcha. You're getting more complete reporting coverage. Sounds
> good to me. Thanks!
>
> Acked-by: Kees Cook <keescook@chromium.org>

Applied to my lkdtm -next tree.

--=20
Kees Cook