Date: Thu, 30 Nov 2017 10:38:03 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Kees Cook' <keescook@...omium.org> CC: Linus Torvalds <torvalds@...ux-foundation.org>, "Tobin C. Harding" <me@...in.cc>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "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 Krcmár <rkrcmar@...hat.com>, "Linux Kernel Mailing List" <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>, Andrew Morton <akpm@...ux-foundation.org> Subject: RE: [PATCH V11 4/5] vsprintf: add printk specifier %px From: Kees Cook > Sent: 29 November 2017 22:28 > On Wed, Nov 29, 2017 at 2:07 AM, David Laight <David.Laight@...lab.com> wrote: > > From: Linus Torvalds > >> Sent: 29 November 2017 02:29 > >> > >> On Tue, Nov 28, 2017 at 6:05 PM, Tobin C. Harding <me@...in.cc> wrote: > >> > > >> > Let's add specifier %px as a > >> > clear, opt-in, way to print a pointer and maintain some level of > >> > isolation from all the other hex integer output within the Kernel. > >> > >> Yes, I like this model. It's easy and it's obvious ("'x' for hex"), > >> and it gives people a good way to say "yes, I really want the actual > >> address as hex" for if/when the hashed pointer doesn't work for some > >> reason. > > > > Remind me to change every %p to %px on kernels that support it. > > > > Although the absolute values of pointers may not be useful, knowing > > that two pointer differ by a small amount is useful. > > It is also useful to know whether pointers are to stack, code, static > > data or heap. > > > > This change to %p is going to make debugging a nightmare. > > In the future, maybe we could have a knob: unhashed, hashed (default), > or zeroed. Add a 4th, hashed_page+offset. Isn't there already a knob for %pK, bits in the same value could be used. That would make it easy to ensure that %pK is more restructive than %p. David
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