linux-kernel - Re: [PATCH 1/2] security, perf: allow further restriction of perf_event

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Message-ID: <20160802130457.GD26514@kernel.org>
Date:	Tue, 2 Aug 2016 10:04:57 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jeff Vander Stoep <jeffv@...gle.com>,
	kernel-hardening@...ts.openwall.com, mingo@...hat.com,
	alexander.shishkin@...ux.intel.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] security, perf: allow further restriction of
 perf_event_open

Em Tue, Aug 02, 2016 at 11:52:43AM +0200, Peter Zijlstra escreveu:
> On Wed, Jul 27, 2016 at 07:45:46AM -0700, Jeff Vander Stoep wrote:
> > When kernel.perf_event_paranoid is set to 3 (or greater), disallow
> > all access to performance events by users without CAP_SYS_ADMIN.

> > This new level of restriction is intended to reduce the attack
> > surface of the kernel. Perf is a valuable tool for developers but
> > is generally unnecessary and unused on production systems. Perf may
> > open up an attack vector to vulnerable device-specific drivers as
> > recently demonstrated in CVE-2016-0805, CVE-2016-0819,
> > CVE-2016-0843, CVE-2016-3768, and CVE-2016-3843.
 
> We have bugs we fix them, we don't kill complete infrastructure because
> of them.
 
> > This new level of
> > restriction allows for a safe default to be set on production systems
> > while leaving a simple means for developers to grant access [1].
 
> So the problem I have with this is that it will completely inhibit
> development of things like JITs that self-profile to re-compile
> frequently used code.

Or reimplement strace with sys_perf_event_open(), speeding it up greatly
by not using ptrace (see 'perf trace', one such attempt), combining it
with sys_bpf(), which can run unpriviledged as well, provides lots of
possibilities for efficient tooling that would be greatly stiffled by
such big hammer restrictions :-(
 
> I would much rather have an LSM hook where the security stuff can do
> more fine grained control of things. Allowing some apps perf usage while
> denying others.

- Arnaldo