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Date: Mon, 30 Oct 2017 15:03:21 -0700
From: Kees Cook <keescook@...omium.org>
To: "Tobin C. Harding" <me@...in.cc>
Cc: kernel-hardening@...ts.openwall.com, 
	"Jason A. Donenfeld" <Jason@...c4.com>, "Theodore Ts'o" <tytso@....edu>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Paolo Bonzini <pbonzini@...hat.com>, 
	Tycho Andersen <tycho@...ker.com>, "Roberts, William C" <william.c.roberts@...el.com>, 
	Tejun Heo <tj@...nel.org>, Jordan Glover <Golden_Miller83@...tonmail.ch>, 
	Greg KH <gregkh@...uxfoundation.org>, Petr Mladek <pmladek@...e.com>, 
	Joe Perches <joe@...ches.com>, Ian Campbell <ijc@...lion.org.uk>, 
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <wilal.deacon@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>, 
	Daniel Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V8 0/2] printk: hash addresses printed with %p

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

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