linux-kernel - RE: [PATCH V11 4/5] vsprintf: add printk specifier %px

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Message-ID: <324abe19f1ee4177911d2fc48899ac8a@AcuMS.aculab.com>
Date:   Wed, 29 Nov 2017 10:07:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        "Tobin C. Harding" <me@...in.cc>
CC:     "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "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>,
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        Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
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        Catalin Marinas <catalin.marinas@....com>,
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        Radim Krcmár <rkrcmar@...hat.com>,
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        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
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        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: 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.

	David