linux-kernel - RE: [PATCH V11 0/5] hash addresses printed with %p

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Date:   Thu, 30 Nov 2017 10:23:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andrew Morton' <akpm@...ux-foundation.org>,
        "Tobin C. Harding" <me@...in.cc>
CC:     "kernel-hardening@...ts.openwall.com" 
        <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 Krcmár <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <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

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