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Message-Id: <20171129152040.ed5b28c198093de8968aac9b@linux-foundation.org>
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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