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Date: Tue, 28 Nov 2017 17:44:54 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Linus Torvalds' <torvalds@...ux-foundation.org>, "Eric W. Biederman"
<ebiederm@...ssion.com>
CC: "Tobin C. Harding" <me@...in.cc>, "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 Krcmár <rkrcmar@...hat.com>, "Linux Kernel Mailing
List" <linux-kernel@...r.kernel.org>, KVM list <kvm@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: RE: [PATCH 0/5] add printk specifier %px, unique identifier
From: Linus Torvalds
> Sent: 28 November 2017 17:33
>
> On Mon, Nov 27, 2017 at 10:26 PM, Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
> >>
> >> Oh well, I just did /proc/<pid>/stack by making it just print 0
> >> unconditionally rather than the hex number.
> >
> > Patch?
>
> Oh, apparently I never pushed out yesterday.
>
> The patch literally just affects the (useless) hex number. So:
>
> cat /proc/self/stack
>
> now prints out
>
> [<0>] proc_pid_stack+0xaa/0x100
> [<0>] proc_single_show+0x48/0x80
> [<0>] seq_read+0xd2/0x410
> ...
>
> instead of putting some randomized kernel address there.
Not sure I've done it on Linux - getting a hexdump of the stack is hard.
But I know I've used the absolute return addresses to help hand-decode
the stack.
Usually needed to work out which stack frame is which - especially when the
stack decode doesn't actually (obviously) contain the addresses of each frame.
I don't know how these new stack traceback methods work, but the best one
I've seen in the past disassembled forwards remembering the stack offset
and unprocessed branch targets until it found a return address.
It only had to track %sp and %bp.
David
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