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Date: Wed, 29 Nov 2017 15:20:40 -0800
From: Andrew Morton <>
To: "Tobin C. Harding" <>
Cc:, Linus Torvalds
 <>, "Jason A. Donenfeld" <>,
 "Theodore Ts'o" <>, Kees Cook <>, Paolo
 Bonzini <>, Tycho Andersen <>,
 "Roberts, William C" <>, Tejun Heo
 <>, Jordan Glover <>, Greg KH
 <>, Petr Mladek <>, Joe Perches
 <>, Ian Campbell <>, Sergey Senozhatsky
 <>, Catalin Marinas <>,
 Will Deacon <>, Steven Rostedt <>,
 Chris Fries <>, Dave Weinstein <>, Daniel
 Micay <>, Djalal Harouni <>, Radim
 Krčmář <>,, Network Development <>,
 David Miller <>, Stephen Rothwell
 <>, Andrey Ryabinin <>,
 Alexander Potapenko <>, Dmitry Vyukov <>
Subject: Re: [PATCH V11 0/5] hash addresses printed with %p

On Wed, 29 Nov 2017 13:05:00 +1100 "Tobin C. Harding" <> 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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