linux-kernel - Re: [RFC] improve_stack: make stack dump output useful again

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Date:	Fri, 14 Mar 2014 15:08:24 -0400
From:	Dave Jones <davej@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] improve_stack: make stack dump output useful again

On Fri, Mar 14, 2014 at 11:31:11AM -0700, Kees Cook wrote:
 > On Thu, Mar 13, 2014 at 4:12 PM, Dave Jones <davej@...hat.com> wrote:
 > > On Thu, Mar 13, 2014 at 03:03:41PM -0700, Linus Torvalds wrote:
 > >
 > >  > You need to look at the *symbol* number. In this output:
 > >  >
 > >  >      [<ffffffff810020c2>] do_one_initcall+0xc2/0x1e0
 > >  >
 > >  > that "ffffffff810020c2" is crap, and is going away. The address that
 > >  > is meaningful and valid is the "do_one_initcall+0xc2" part.
 > >  >
 > >  > *That* is the part you'd use to parse in user space.
 > >  >
 > >  > Try it today with the CONFIG_RANDOMIZE_BASE option to see. Using the
 > >  > hex number doesn't *work*.
 > >
 > > That reminds me, perf top is still busted when this option is enabled.
 > 
 > Hrm, works for me. I'm not very familiar with what to expect, but
 > comparing output between kaslr boot and nokaslr boot, it looks the
 > same to me.

ok, nokalsr makes it work too.
Booting with that and using the perf binary from 3.14rc6 , I just see..

  9.30%  [kernel]                      [k] 0xffffffffaf18e887
  7.98%  [kernel]                      [k] 0xffffffffaf3276c7
  6.10%  [kernel]                      [k] 0xffffffffaf18dd3a
  4.39%  [kernel]                      [k] 0xffffffffaf327717
  1.71%  [kernel]                      [k] 0xffffffffaf18e89c
  1.52%  [kernel]                      [k] 0xffffffffaf3276cc

Curiously, if I use the perf binary from 3.13, I see everything lumped together as..

 95.89%  [kernel].exit.text            [k] 0x000000002e586c26

(When kaslr is disabled both binaries work fine)

Also maybe related: The rc6 binary claims it can't read symbols from vmlinux
when kaslr is enabled.

	Dave

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