From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754100AbdK2KHh (ORCPT <rfc822;w@1wt.eu>);
        Wed, 29 Nov 2017 05:07:37 -0500
Received: from smtp-out4.electric.net ([192.162.216.182]:64026 "EHLO
        smtp-out4.electric.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751396AbdK2KHc (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 29 Nov 2017 05:07:32 -0500
From: David Laight <David.Laight@ACULAB.COM>
To: "'Linus Torvalds'" <torvalds@linux-foundation.org>,
        "Tobin C. Harding" <me@tobin.cc>
CC: "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        "Theodore Ts'o" <tytso@mit.edu>, Kees Cook <keescook@chromium.org>,
        Paolo Bonzini <pbonzini@redhat.com>, Tycho Andersen <tycho@tycho.ws>,
        "Roberts, William C" <william.c.roberts@intel.com>,
        "Tejun Heo" <tj@kernel.org>,
        Jordan Glover <Golden_Miller83@protonmail.ch>,
        Greg KH <gregkh@linuxfoundation.org>, Petr Mladek <pmladek@suse.com>,
        Joe Perches <joe@perches.com>, Ian Campbell <ijc@hellion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <wilal.deacon@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>, Chris Fries <cfries@google.com>,
        Dave Weinstein <olorin@google.com>,
        "Daniel Micay" <danielmicay@gmail.com>,
        Djalal Harouni <tixxdz@gmail.com>,
        =?utf-8?B?UmFkaW0gS3JjbcOhcg==?= <rkrcmar@redhat.com>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        David Miller <davem@davemloft.net>,
        "Stephen Rothwell" <sfr@canb.auug.org.au>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: RE: [PATCH V11 4/5] vsprintf: add printk specifier %px
Thread-Topic: [PATCH V11 4/5] vsprintf: add printk specifier %px
Thread-Index: AQHTaLnlNbdOW8vPZEqlErHdKDS3dKMrISKg
Date: Wed, 29 Nov 2017 10:07:27 +0000
Message-ID: <324abe19f1ee4177911d2fc48899ac8a@AcuMS.aculab.com>
References: <1511921105-3647-1-git-send-email-me@tobin.cc>
 <1511921105-3647-5-git-send-email-me@tobin.cc>
 <CA+55aFxgGb13hqoNQ8bzFn4ENZM25PBSdi5pkFUBa5Hk+j-s3Q@mail.gmail.com>
In-Reply-To: <CA+55aFxgGb13hqoNQ8bzFn4ENZM25PBSdi5pkFUBa5Hk+j-s3Q@mail.gmail.com>
Accept-Language: en-GB, en-US
Content-Language: en-US
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: [10.202.99.200]
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
X-Outbound-IP: 156.67.243.126
X-Env-From: David.Laight@ACULAB.COM
X-Proto: esmtps
X-Revdns: 
X-HELO: AcuMS.aculab.com
X-TLS: TLSv1.2:ECDHE-RSA-AES256-SHA384:256
X-Authenticated_ID: 
X-PolicySMART: 3396946, 3397078
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from base64 to 8bit by nfs id vATA7h6w014058

From: Linus Torvalds
> Sent: 29 November 2017 02:29
> 
> On Tue, Nov 28, 2017 at 6:05 PM, Tobin C. Harding <me@tobin.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