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Date: Sun, 4 Jan 2015 17:10:49 +0100
From: Jiri Olsa <jolsa@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
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Subject: Re: =?utf-8?B?562U5aSN77yaW1BBVENIXSBwZXJm?= =?utf-8?Q?_core=3A_Us?=
 =?utf-8?Q?e?= KSTK_ESP() instead of pt_regs->sp while output user regs
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On Tue, Dec 30, 2014 at 08:03:27PM +0100, Peter Zijlstra wrote:
> On Thu, Dec 25, 2014 at 07:48:28AM -0800, Andy Lutomirski wrote:
> > On a quick look, there are plenty of other bugs in there besides just
> > the stack pointer issue.  The ABI check that uses TIF_IA32 in the perf
> > core is completely wrong.  TIF_IA32 may be equal to the actual
> > userspace bitness by luck, but, if so, that's more or less just luck.
> > And there's a user_mode test that should be user_mode_vm.
> > 
> > Also, it's not just sp that's wrong.  There are various places that
> > you can interrupt in which many of the registers have confusing
> > locations.  You could try using the cfi unwind data, but that's
> > unlikely to work for regs like cs and ss, and, during context switch,
> > this has very little chance of working.
> > 
> > What's the point of this feature?  Honestly, my suggestion would be to
> > delete it instead of trying to fix it.  It's also not clear to me that
> > there aren't serious security problems here -- it's entirely possible
> > for sensitive *kernel* values to and up in task_pt_regs at certain
> > times, and if you run during context switch and there's no code to
> > suppress this dump during context switch, then you could be showing
> > regs that belong to the wrong task.
> 
> Of course the people who actually wrote the code are not on CC :/
> 
> There's two users of this iirc;
> 
>  1) the dwarf stack unwinder thingy, which basically dumps the userspace
>  regs and the top of userspace stack on 'event'.

looks like this solves the issue I was trying to fix
long time ago:
  http://marc.info/?l=linux-kernel&m=134934717011451&w=2

this seems a lot simpler ;-) I'll test..

jirka