linux-kernel - Re: [PATCH 1/3] perf/x86/intel: output LBR support statement after validation

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Date:	Sun, 5 Jun 2016 18:59:35 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	David Carrillo-Cisneros <davidcc@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	Kan Liang <kan.liang@...el.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/3] perf/x86/intel: output LBR support statement after
 validation

> It is not because you force LBR to ring3 only that you do not capture
> kernel addresses in the FROM field.
> Keep in mind that LBR priv level filtering applies to the target of
> the branch and not the source. You might
> still get a kernel address if returning from kernel. Now, in callstack
> mode, I think the return branch is never
> actually recorded in the LBR, it just causes a pop, so theoretically
> this should not happen. I'd like to be
> 100% sure of that, though.

Far branches shouldn't be included in call stack LBR. Don't think
there is any other situation where the ring 0 address could leak either.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only