linux-kernel - Re: [PATCH 0/2] perf, intel: Add support for PEBS output to Intel PT

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Message-ID: <20190508103924.GF2606@hirez.programming.kicks-ass.net>
Date:   Wed, 8 May 2019 12:39:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        jolsa@...hat.com, adrian.hunter@...el.com
Subject: Re: [PATCH 0/2] perf, intel: Add support for PEBS output to Intel PT

On Thu, May 02, 2019 at 01:50:20PM +0300, Alexander Shishkin wrote:
> Hi Peter,
> 
> New PEBS feature: output to Intel PT stream instead of the DS area. It's
> theoretically useful in virtualized environments, where DS area can't be
> used. It's also good for those who are interested in instruction trace for
> context of the PEBS events. As PEBS goes, it can provide LBR context with
> all the branch-related information that PT doesn't provide at the moment.
> 
> PEBS records are packetized in the PT stream, so instead of extracting
> them in the PMI, we leave it to the perf tool, because real time PT
> decoding is not practical. Tooling patches are not included, but can be
> found here [1].
> 
> Added is an attribute bit 'aux_source' to mean that an event is a source of
> AUX data. This bit enables PEBS output to PT.

There is a distinct lack of permission checks in this. When creating
this construct we should verify the creator has access to PT. And we
should verify we're not (accidentally or otherwise) writing into someone
else's PT buffers.