Date: Wed, 29 Nov 2017 15:20:58 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: "Tobin C. Harding" <me@...in.cc> Cc: 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 Krčmář <rkrcmar@...hat.com>, 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 4/5] vsprintf: add printk specifier %px On Wed, 29 Nov 2017 13:05:04 +1100 "Tobin C. Harding" <me@...in.cc> wrote: > printk specifier %p now hashes all addresses before printing. Sometimes > we need to see the actual unmodified address. This can be achieved using > %lx but then we face the risk that if in future we want to change the > way the Kernel handles printing of pointers we will have to grep through > the already existent 50 000 %lx call sites. 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. > > Add printk specifier %px to print the actual unmodified address. > > ... > > +Unmodified Addresses > +==================== > + > +:: > + > + %px 01234567 or 0123456789abcdef > + > +For printing pointers when you _really_ want to print the address. Please > +consider whether or not you are leaking sensitive information about the > +Kernel layout in memory before printing pointers with %px. %px is > +functionally equivalent to %lx. %px is preferred to %lx because it is more > +uniquely grep'able. If, in the future, we need to modify the way the Kernel > +handles printing pointers it will be nice to be able to find the call > +sites. > + You might want to add a checkpatch rule which emits a stern do-you-really-want-to-do-this warning when someone uses %px.
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