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Date: Thu, 30 Nov 2017 10:23:44 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Andrew Morton' <akpm@...ux-foundation.org>, "Tobin C. Harding"
	<me@...in.cc>
CC: "kernel-hardening@...ts.openwall.com"
	<kernel-hardening@...ts.openwall.com>, Linus Torvalds
	<torvalds@...ux-foundation.org>, "Jason A. Donenfeld" <Jason@...c4.com>,
	Theodore Ts'o <tytso@....edu>, Kees Cook <keescook@...omium.org>, "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>, Catalin Marinas <catalin.marinas@....com>,
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 Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>,
	Radim Krcm√°r <rkrcmar@...hat.com>,
	"linux-kernel@...r.kernel.org" <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>
Subject: RE: [PATCH V11 0/5] hash addresses printed with %p

From: Andrew Morton
> Sent: 29 November 2017 23:21
> >
> > The added advantage of hashing %p is that security is now opt-out, if
> > you _really_ want the address you have to work a little harder and use
> > %px.

You need a system-wide opt-out that prints the actual values.
Otherwise developers will use something else to print addresses and
the code will remain in the released drivers.

> > The idea for creating the printk specifier %px to print the actual
> > address was suggested by Kees Cook (see below for email threads by
> > subject).
> 
> Maybe I'm being thick, but...  if we're rendering these addresses
> unusable by hashing them, why not just print something like
> "<obscured>" in their place?  That loses the uniqueness thing but I
> wonder how valuable that is in practice?

My worry is that is you get a kernel 'oops' print with actual register
values you have no easy way of tying an address or address+offset to
the corresponding hash(address) printed elsewhere.

	David

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