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

[Kees Cook]

On Wed, Jan 9, 2019 at 7:16 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Tue, Jan 8, 2019 at 10:31 PM Christophe Leroy
> <christophe.leroy@xxxxxx> wrote:
> >
> >
> >
> > Le 09/01/2019 Ã 02:14, Kees Cook a Ãcrit :
> > > On Fri, Dec 14, 2018 at 7:26 AM Christophe Leroy
> > > <christophe.leroy@xxxxxx> 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@xxxxxxxxxxxx>

Applied to my lkdtm -next tree.

-- 
Kees Cook