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

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Message-ID: <20160617200050.GL13337@kernel.org>
Date:	Fri, 17 Jun 2016 17:00:50 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Daniel Micay <danielmicay@...il.com>
Cc:	kernel-hardening@...ts.openwall.com,
	Kees Cook <keescook@...omium.org>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-doc@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Namhyung Kim <namhyung@...nel.org>,
	David Ahern <dsahern@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] [PATCH 2/2] security,perf: Allow further
 restriction of perf_event_open

Em Fri, Jun 17, 2016 at 12:16:47PM -0400, Daniel Micay escreveu:
> On Fri, 2016-06-17 at 08:54 +0200, Peter Zijlstra wrote:
> > This Changelog is completely devoid of information. _WHY_ are you
> > doing this?

> Attack surface reduction. It's possible to use seccomp-bpf for some
> limited cases, but it's not flexible enough. There are lots of
> information leaks and local privilege escalation vulnerabilities via
> perf events, yet on most Linux installs it's not ever being used. So
> turning it off by default on those installs is an easy win. The holes
> are reduced to root -> kernel (and that's not a meaningful boundary in
> mainline right now - although as is the case here, Debian has a bunch of
> securelevel patches for that).

Is ptrace also disabled on such systems, or any of the other more recent
syscalls? The same arguments could probably be used to disable those:
reduce attack surface, possibly the new ones have bugs as they are
relatively new and it takes a long time for new syscalls to be more
generally used, if we go on disabling them in such a way, they will
probably never get used :-\

Wouldn't the recent bump in perf_event_paranoid to 2 enough? I.e. only
allow profiling of user tasks?

Or is there something more specific that we should disable/constrain to
reduce such surface contact without using such a big hammer?

- Arnaldo