Re: [PATCH] printk: introduce kptr_restrict level 3

From: Kees Cook
Date: Thu Oct 06 2016 - 17:26:20 EST

On Thu, Oct 6, 2016 at 2:19 PM, Joe Perches <joe@xxxxxxxxxxx> wrote:
> On Thu, 2016-10-06 at 14:00 -0700, Kees Cook wrote:
>> And based on my read of this thread, we all appear to be in violent
>> agreement. :) "always protect %p" is absolutely the goal, and we can
>> figure out the best way to get there.
> I proposed emitting pointers from the const and text sections by default
> and using NULL for data pointers.

Leaks of const and text (while not useful for write-attacks) can leak
KASLR offset (though yes, yes, there are many existing leaks -- but we
should avoid adding a new one regardless).

I think the logic of "is this destined for userspace" is likely the
cleanest approach. There still may be many things this breaks, though.
(I expect perf. Everything breaks perf. ;)


Kees Cook
Nexus Security