linux-kernel - Re: [PATCH] lkdtm: Add a tests for NULL pointer dereference

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Date:   Wed, 9 Jan 2019 12:05:02 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] lkdtm: Add a tests for NULL pointer dereference

On Wed, Jan 9, 2019 at 7:16 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Tue, Jan 8, 2019 at 10:31 PM Christophe Leroy
> <christophe.leroy@....fr> wrote:
> >
> >
> >
> > Le 09/01/2019 à 02:14, Kees Cook a écrit :
> > > On Fri, Dec 14, 2018 at 7:26 AM Christophe Leroy
> > > <christophe.leroy@....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" : "paging 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/commit/?id=49a502ea23bf9dec47f8f3c3960909ff409cd1bb),
> > 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@...omium.org>

Applied to my lkdtm -next tree.

-- 
Kees Cook