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Date: Thu, 30 Nov 2017 10:23:44 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Andrew Morton' <>, "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 Krcm√°r <>,
	"" <>, "Network
 Development" <>, David Miller <>,
	Stephen Rothwell <>, Andrey Ryabinin
	<>, Alexander Potapenko <>, "Dmitry
 Vyukov" <>
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.


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