linux-kernel - Re: [PATCH V9 00/10] arm64/perf: Enable branch stack sampling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZB2MPqqBjzyaMlrd@sirena.org.uk>
Date:   Fri, 24 Mar 2023 11:40:46 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        will@...nel.org, catalin.marinas@....com, mark.rutland@....com,
        James Clark <james.clark@....com>,
        Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Suzuki Poulose <suzuki.poulose@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V9 00/10] arm64/perf: Enable branch stack sampling

On Fri, Mar 24, 2023 at 08:50:32AM +0530, Anshuman Khandual wrote:
> On 3/23/23 18:24, Mark Brown wrote:
> > On Thu, Mar 23, 2023 at 09:55:47AM +0530, Anshuman Khandual wrote:

> >> By default entire SYS_HFGITR_EL2 is set as cleared during init and that would
> >> prevent a guest from using BRBE.

> > It should prevent the host as well shouldn't it? 

> In a EL2 host environment, BRBE is being enabled either in EL2 (kernel/hv) or
> in EL0 (user space), it never gets enabled on EL1. Moreover BRBIALL/BRBINJ
> instructions are always executed while being inside EL2 (kernel/hv). Hence how
> could these instructions cause trap in EL2 ?

Ah, I see - I didn't realise this couldn't run at EL1.

> > Yes, looks roughly what I'd expect.

> I could send an stand alone patch after your latest series [1], which disables
> BRBINJ/BRBIALL instruction trap in EL2 to enable BRBE usage in the guest.

Sounds resaonable enough to me.

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)