Date: Wed, 29 Nov 2017 15:20:40 -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 0/5] hash addresses printed with %p On Wed, 29 Nov 2017 13:05:00 +1100 "Tobin C. Harding" <me@...in.cc> wrote: > Currently there exist approximately 14 000 places in the Kernel where > addresses are being printed using an unadorned %p. This potentially > leaks sensitive information regarding the Kernel layout in memory. Many > of these calls are stale, instead of fixing every call lets hash the > address by default before printing. This will of course break some > users, forcing code printing needed addresses to be updated. We can add > a printk specifier for this purpose (%px) to give developers a clear > upgrade path for breakages caused by applying this patch set. > > 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. > > 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?
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