Date: Tue, 5 Dec 2017 13:08:41 -0800 From: Randy Dunlap <rdunlap@...radead.org> To: David Laight <David.Laight@...LAB.COM>, '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 On 11/30/2017 02:38 AM, David Laight wrote: > 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. (yeah, I'm kind of behind on this thread.) This kind of option (with default hashed) is what I was just thinking of after having seen a few unhelpful traces. But then the knob might not be changed in time for the traces either. :( -- ~Randy
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