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

From: Andi Kleen
Date: Sun Jun 05 2016 - 21:59:50 EST

> 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.

ak@xxxxxxxxxxxxxxx -- Speaking for myself only