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SubjectRe: [RFC] improve_stack: make stack dump output useful again
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On Fri, Mar 14, 2014 at 12:08 PM, Dave Jones <davej@redhat.com> wrote:
> 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@redhat.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.

Very odd. The perf I built from Linus's tree seems to resolve
everything fine for me. I wonder what we're doing differently. I
literally just did "cd tools/perf; make; scp perf
root@test-machine:/root; ssh root@test-machine 'perf top'" and
everything looks fine.

-Kees

--
Kees Cook
Chrome OS Security


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