linux-kernel - Re: Tightening up rdpmc permissions?

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Message-ID: <9930.1412012182@turing-police.cc.vt.edu>
Date:	Mon, 29 Sep 2014 13:36:22 -0400
From:	Valdis.Kletnieks@...edu
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Tightening up rdpmc permissions?

On Mon, 29 Sep 2014 09:39:16 -0700, Andy Lutomirski said:

> Would it make sense to restrict rdpmc to tasks that are in mms that
> have a perf_event mapping?  After all, unless I misunderstand
> something, user code can't reliably use rdpmc unless they've mapped a
> perf_event object to check the rdpmc bit and figure out what ecx value
> to use.

Wouldn't that be trivially easy for an attacker to bypass? Just map a dummy
perf_event object  and then go to town?

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