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Date: Wed, 29 Nov 2017 15:20:40 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Tobin C. Harding" <me@...in.cc>
Cc: 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>,
 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>, Radim
 Krčmář <rkrcmar@...hat.com>,
 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

On Wed, 29 Nov 2017 13:05:00 +1100 "Tobin C. Harding" <me@...in.cc> wrote:

> Currently there exist approximately 14 000 places in the Kernel where
> addresses are being printed using an unadorned %p. This potentially
> leaks sensitive information regarding the Kernel layout in memory. Many
> of these calls are stale, instead of fixing every call lets hash the
> address by default before printing. This will of course break some
> users, forcing code printing needed addresses to be updated. We can add
> a printk specifier for this purpose (%px) to give developers a clear
> upgrade path for breakages caused by applying this patch set.
> 
> 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.
> 
> 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?


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