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Date: Thu, 30 Nov 2017 10:38:03 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Kees Cook' <keescook@...omium.org>
CC: Linus Torvalds <torvalds@...ux-foundation.org>, "Tobin C. Harding"
	<me@...in.cc>, "kernel-hardening@...ts.openwall.com"
	<kernel-hardening@...ts.openwall.com>, "Jason A. Donenfeld"
	<Jason@...c4.com>, Theodore Ts'o <tytso@....edu>, Paolo Bonzini
	<pbonzini@...hat.com>, Tycho Andersen <tycho@...ho.ws>, "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>,
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	<danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>,
	Radim Krcm√°r <rkrcmar@...hat.com>, "Linux Kernel Mailing
 List" <linux-kernel@...r.kernel.org>, Network Development
	<netdev@...r.kernel.org>, David Miller <davem@...emloft.net>, "Stephen
 Rothwell" <sfr@...b.auug.org.au>, Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: RE: [PATCH V11 4/5] vsprintf: add printk specifier %px

From: Kees Cook
> Sent: 29 November 2017 22:28
> On Wed, Nov 29, 2017 at 2:07 AM, David Laight <David.Laight@...lab.com> wrote:
> > From: Linus Torvalds
> >> Sent: 29 November 2017 02:29
> >>
> >> On Tue, Nov 28, 2017 at 6:05 PM, Tobin C. Harding <me@...in.cc> wrote:
> >> >
> >> >    Let's add specifier %px as a
> >> > clear, opt-in, way to print a pointer and maintain some level of
> >> > isolation from all the other hex integer output within the Kernel.
> >>
> >> Yes, I like this model. It's easy and it's obvious ("'x' for hex"),
> >> and it gives people a good way to say "yes, I really want the actual
> >> address as hex" for if/when the hashed pointer doesn't work for some
> >> reason.
> >
> > Remind me to change every %p to %px on kernels that support it.
> >
> > Although the absolute values of pointers may not be useful, knowing
> > that two pointer differ by a small amount is useful.
> > It is also useful to know whether pointers are to stack, code, static
> > data or heap.
> >
> > This change to %p is going to make debugging a nightmare.
> 
> In the future, maybe we could have a knob: unhashed, hashed (default),
> or zeroed.

Add a 4th, hashed_page+offset.

Isn't there already a knob for %pK, bits in the same value could be used.
That would make it easy to ensure that %pK is more restructive than %p.

	David

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