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

[Kees Cook]

On Wed, Oct 25, 2017 at 7:53 PM, Tobin C. Harding <me@xxxxxxxx> 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
1837

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.

-Kees

-- 
Kees Cook
Pixel Security