Re: [PATCH] lkdtm: Test KUAP directional user access unlocks on powerpc

[Christophe Leroy]

Le 31/01/2020 Ã 07:53, Russell Currey a ÃcritÂ:
> On Fri, 2020-01-31 at 07:44 +0100, Christophe Leroy wrote:
> > Le 31/01/2020 Ã 06:31, Russell Currey a Ãcrit :
> > > +	pr_info("attempting bad read at %px with write allowed\n",
> > > ptr);
> > > +	tmp = *ptr;
> > > +	tmp += 0xc0dec0de;
> > > +	prevent_write_to_user(ptr, sizeof(unsigned long));
> >
> > Does it work ? I would have thought that if the read fails the
> > process
> > will die and the following test won't be performed.
>
> Correct, the ACCESS_USERSPACE test does the same thing.  Splitting this
> into separate R and W tests makes sense, even if it is unlikely that
> one would be broken without the other.

Or once we are using user_access_begin() stuff, we can use 
unsafe_put_user() and unsafe_get_user() which should return an error 
instead of killing the caller.

Christophe