linux-kernel - Re: [BUG] perf: bogus correlation of kernel symbols

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Date:	Thu, 12 May 2011 23:50:23 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] perf: bogus correlation of kernel symbols


* Stephane Eranian <eranian@...gle.com> wrote:

> On Thu, May 12, 2011 at 11:35 PM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > * Stephane Eranian <eranian@...gle.com> wrote:
> >
> >> The other contradiction, I see, is that you have perf_event paranoia level
> >> and this new kptr masquerading feature which conflict with each
> >> other.
> >>
> >> You can be allowed to monitor at the kernel level (paranoid=1, default)
> >> but you cannot correlate symbols:
> >>
> >> $ perf record -e cycles:k foo
> >>
> >> I suspect if you have this kptr thing turned on, then you need to disallow
> >> monitoring at the kernel level too.
> >
> > The better (and consistent) solution would be to turn the kptr_restrict thing
> > off - see the patch i sent.
>
> I saw that. But I think that when someone turns it back on, then you need to 
> increase the perf_events paranoia level to disallow kernel monitoring to 
> regular users such that you maintain consistency across the board.

Dunno, i would not couple them necessarily - certain users might still have 
access to kernel symbols via some other channel - for example the System.map.

Thanks,

	Ingo
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