linux-kernel - Re: [tip:perf/urgent] perf symbols: Handle /proc/sys/kernel/kptr

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Message-ID: <20110527155714.GD2349@ghostprotocols.net>
Date:	Fri, 27 May 2011 12:57:14 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	paulus@...ba.org, hpa@...or.com, mingo@...hat.com,
	eranian@...gle.com, tzanussi@...il.com, penberg@...helsinki.fi,
	efault@....de, peterz@...radead.org, davej@...hat.com,
	davem@...emloft.net, fweisbec@...il.com, kees.cook@...onical.com,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf symbols: Handle
	/proc/sys/kernel/kptr_restrict

Em Fri, May 27, 2011 at 08:46:42AM -0700, Linus Torvalds escreveu:
> On Fri, May 27, 2011 at 1:35 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > I think the biggest problem is that it is yelling at us even when i'm
> > root - and root can access all the pointer values just fine:
> 
> Instead of looking at the kptr_restrict file, please just look at the
> addresses in the kallsyms file, and if they are all zero, you know
> that it's not a usable kallsyms file (and you can pretty much assume
> that it's due to kptr_restrict).
> 
> So I think the whole symbol__read_kptr_restrict() thing is just
> pointless. Don't do it.

I thought about that, ended up using the file not to rely on the values
on kallsyms, too much future proofing, I guess.

BTW, the problem reported by Ingo above (yelling even for root) is not a
bug, he ran 'perf record' as non root with kptr_restrict set and then
ran 'perf report' as root.

- Arnaldo
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