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From: David Laight <David.Laight@ACULAB.COM>
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Subject: RE: [PATCH V11 0/5] hash addresses printed with %p
Thread-Topic: [PATCH V11 0/5] hash addresses printed with %p
Thread-Index: AQHTaWjAiUqbZXoc7UqTW5a19cDn2KMsthDA
Date: Thu, 30 Nov 2017 10:23:44 +0000
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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.

	David