[kernel-hardening] Re: [PATCH V8 0/2] printk: hash addresses printed with %p

[Joe Perches <joe@perches.com>]

On Tue, 2017-10-31 at 09:33 +1100, Tobin C. Harding wrote:
> On Mon, Oct 30, 2017 at 03:03:21PM -0700, Kees Cook wrote:
> > On Wed, Oct 25, 2017 at 7:53 PM, Tobin C. Harding <me@tobin.cc> wrote:
> > > Here is the behaviour that this set implements.
> > > 
> > > For kpt_restrict==0
> > > 
> > > Randomness not ready:
> > >   printed with %p:              (pointer)          # NOTE: with padding
> > > Valid pointer:
> > >   printed with %pK:             deadbeefdeadbeef
> > >   printed with %p:              0xdeadbeef
> > >   malformed specifier (eg %i):  0xdeadbeef
> > 
> > I really think we can't include SPECIAL unless _every_ callsite of %p
> > is actually doing "0x%p", and then we're replacing all of those. We're
> > not doing that, though...
> > 
> > $ git grep '%p\b' | wc -l
> > 12766
> > $ git grep '0x%p\b' | wc -l
> > 18370x
> > 
> > If we need some kind of special marking that this is a hashed
> > variable, that should be something other than "0x". If we're using the
> > existing "(null)" and new "(pointer)" text, maybe "(hash:xxxxxx)"
> > should be used instead? Then the (rare) callers with 0x become
> > "0x(hash:xxxx)" and naked callers produce "(hash:xxxx)".
> > 
> > I think the first step for this is to just leave SPECIAL out.
> 
> Thanks Kees. V9 leaves SPECIAL out. Also V9 prints the whole 64 bit
> address with the first 32 bits masked to zero. The intent being to _not_
> change the output format from what it currently is. So it will look like
> this; 
> 
> 	00000000c09e81d0
> 
> What do you think?
> 
> Amusingly I think this whole conversation is going to come up again
> when we do %pa, in inverse, since %pa currently does us SPECIAL.

I once sent a patch set to remove SPECIAL from %pa
and add 0x where necessary.

https://patchwork.kernel.org/patch/3875471/

After that didn't happen, I removed the duplicated
0x%pa with a sed.

https://patchwork.kernel.org/patch/8509421/

Sending a treewide sed patch would be fine with me.