Re: [RFC 0/5] perf: Per PMU access controls (paranoid setting)

From: Andi Kleen <ak@linux.intel.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Tvrtko Ursulin <tursulin@ursulin.net>,
	LKML <linux-kernel@vger.kernel.org>,
	tvrtko.ursulin@linux.intel.com,
	Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
	Alexey Budankov <alexey.budankov@linux.intel.com>,
	Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>
Subject: Re: [RFC 0/5] perf: Per PMU access controls (paranoid setting)
Date: Fri, 28 Sep 2018 10:23:40 -0700	[thread overview]
Message-ID: <20180928172340.GA32651@tassilo.jf.intel.com> (raw)
In-Reply-To: <20180928164111.i6nba2j6mnegwslw@lakrids.cambridge.arm.com>

> There's also been prior discussion on these feature in other contexts
> (e.g. android expoits resulting from out-of-tree drivers). It would be
> nice to see those considered.
> 
> IIRC The conclusion from prior discussions (e.g. [1]) was that we wanted
> finer granularity of control such that we could limit PMU access to
> specific users -- e.g. disallow arbitrary android apps from poking *any*
> PMU, while allowing some more trusted apps/users to uses *some* specific
> PMUs.
> 
> e.g. we could add /sys/bus/event_source/devices/${PMU}/device, protect
> this via the usual fs ACLs, and pass the fd to perf_event_open()
> somehow. A valid fd would act as a capability, taking precedence over
> perf_event_paranoid.

That sounds like an orthogonal feature. I don't think the original
patchkit would need to be hold up for this. It would be something
in addition.

BTW can't you already do that with the syscall filter? I assume
the Android sandboxes already use that. Just forbid perf_event_open
for the apps.

-Andi