linux-kernel - Re: [PATCH v2 20/39] x86/bugs: Disable Retpoline when IBT

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Message-ID: <20220225022205.yfvpfq5qwpcvrxux@treble>
Date:   Thu, 24 Feb 2022 18:22:05 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, samitolvanen@...gle.com,
        mark.rutland@....com, alyssa.milburn@...el.com, mbenes@...e.cz,
        rostedt@...dmis.org, mhiramat@...nel.org,
        alexei.starovoitov@...il.com
Subject: Re: [PATCH v2 20/39] x86/bugs: Disable Retpoline when IBT

On Thu, Feb 24, 2022 at 05:11:23PM -0800, Kees Cook wrote:
> On Thu, Feb 24, 2022 at 03:51:58PM +0100, Peter Zijlstra wrote:
> > Retpoline and IBT are mutually exclusive. IBT relies on indirect
> > branches (JMP/CALL *%reg) while retpoline avoids them by design.
> > 
> > Demote to LFENCE on IBT enabled hardware.
> 
> What's the expected perf impact of this?

Should make it faster...

-- 
Josh