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Message-Id: <20171129152058.389361d3576e784f47326cac@linux-foundation.org>
Date: Wed, 29 Nov 2017 15:20:58 -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 4/5] vsprintf: add printk specifier %px
On Wed, 29 Nov 2017 13:05:04 +1100 "Tobin C. Harding" <me@...in.cc> wrote:
> printk specifier %p now hashes all addresses before printing. Sometimes
> we need to see the actual unmodified address. This can be achieved using
> %lx but then we face the risk that if in future we want to change the
> way the Kernel handles printing of pointers we will have to grep through
> the already existent 50 000 %lx call sites. 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.
>
> Add printk specifier %px to print the actual unmodified address.
>
> ...
>
> +Unmodified Addresses
> +====================
> +
> +::
> +
> + %px 01234567 or 0123456789abcdef
> +
> +For printing pointers when you _really_ want to print the address. Please
> +consider whether or not you are leaking sensitive information about the
> +Kernel layout in memory before printing pointers with %px. %px is
> +functionally equivalent to %lx. %px is preferred to %lx because it is more
> +uniquely grep'able. If, in the future, we need to modify the way the Kernel
> +handles printing pointers it will be nice to be able to find the call
> +sites.
> +
You might want to add a checkpatch rule which emits a stern
do-you-really-want-to-do-this warning when someone uses %px.
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