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

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Date:   Wed, 19 Oct 2016 10:56:05 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Daniel Micay <danielmicay@...il.com>
Cc:     kernel-hardening@...ts.openwall.com,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jeff Vander Stoep <jeffv@...gle.com>
Subject: Re: [kernel-hardening] [PATCH 1/2] security, perf: allow further
 restriction of perf_event_open

On Tue, Oct 18, 2016 at 05:15:01PM -0400, Daniel Micay wrote:
> It's also worth noting that fine-grained control via a scoped
> mechanism would likely only be used to implement *more restrictions*
> on Android, not to make the feature less aggressive. It's desirable
> for perf events to be disabled by default for non-root across the
> board on Android.  The part that's imperfect is that when a developer
> uses a profiling tool, unprivileged usage is automatically enabled
> across the board until reboot. Ideally, it would be enabled only for
> the scope where it's needed. 

Sure; understood.

> It would be very tricky to implement though, especially without adding
> friction, and it would only have value for protecting devices being
> used for development. It really doesn't seem to be worth the trouble,
> especially since it doesn't persist on reboot. It's only a temporary
> security hole and only for developer devices.

I can see that for Android this isn't much of a win. It is beneficial
elsewhere, and covers a larger set of use-cases.

If perf were a filesystem object, we'd only allow access by a given
'perf' group, and that would be sufficient to avoid most of that
friction (IIUC). I wonder what we can do that's similar.

Thanks,
Mark.