Date: Tue, 28 Nov 2017 12:43:43 +1100 From: "Tobin C. Harding" <me@...in.cc> To: Kees Cook <keescook@...omium.org> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, "Jason A. Donenfeld" <Jason@...c4.com>, Theodore Ts'o <tytso@....edu>, 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>, LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH 0/5] add printk specifier %px, unique identifier On Mon, Nov 27, 2017 at 04:57:18PM -0800, Kees Cook wrote: > On Mon, Nov 27, 2017 at 3:40 PM, Tobin C. Harding <me@...in.cc> wrote: > > Linus, > > > > I know you are bored of this patch set already and this pits your vast > > experience against my eight months kernel dev experience ;) > > > > I humbly maintain that hashing %p and suggesting people use %x > > _correctly_ isn't a WIN solution. > > > > Please don't go easy on me because I'm new, if I'm out of line - say > > so. > > > > This set is based on the following assumptions. > > > > 1. We now have leaking_addresses.pl illuminating leaking addresses. > > 2. We have no _clear_ strategy for fixing leaks once found. > > 3. We do not have a proposed non opt-in solution. > > 4. There is a distinct use case for this specifier. > > > > Patch 1: Corrects the docs for %pK. > > > > Patch 2: Refactors %pK code out of pointer() into helper function. > > > > Patch 3: Adds specifier %px, small 'x' was chosen because the hashed hex > > value is printed in lower case. > > > > Patch 4/5: Provides example usage of new specifier. > > > > The hashing code is based on the work done hashing %p during 4.14 dev > > cycle. > > > > Finally, with this patch set in place, we have the added benefit that > > newbies (me) can quietly go around the kernel 'sweeping up' after > > leaking addresses. This as apposed to using a hammer and hashing all > > %p. And if this is deemed too little and too slow we can always search > > and replace '%p' with '%px'. > > How does this opt-in to %px help? We'll still have %p everywhere. :( > Why not invert this? %p is hashed and %px is the old %p? Then we can > move %x users to %px. This is a really nice twist, I don't know why it hasn't come up before. For the record it - Plugs a bunch of potential current leaks. - Is on by default (*not* opt-in). - Is easy to use (%p if you don't care, %px if you _really_ want the address). - Reduces risk of future developers creating grep hell by using %x (- makes Linus happy because it does everything he has suggested except promote use of %x) > I'd still like to see a default-on solution for this class of leaks... I'll re-spin this tomorrow and see if we can't stop bothering everyone with it :) thanks, Tobin.
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