linux-kernel - Re: [PATCH 15/29] x86: Disable IBT around firmware

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Message-ID: <4DC4ECA7-902C-4496-8AAA-173D86C7C730@chromium.org>
Date:   Mon, 21 Feb 2022 07:54:55 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com,
        linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com
Subject: Re: [PATCH 15/29] x86: Disable IBT around firmware



On February 21, 2022 2:06:15 AM PST, Peter Zijlstra <peterz@...radead.org> wrote:
>
>Could you trim replies so that I can actually find what you write?

Sorry, yes; I was on my phone where the interface is awkward.

>On Mon, Feb 21, 2022 at 12:27:20AM -0800, Kees Cook wrote:
>> Please make these both __always_inline so there no risk of them ever gaining ENDBRs and being used by ROP to disable IBT...
>
>Either that or mark them __noendbr. The below seems to work.
>
>Do we have a preference?

Ah yeah, that works for me.

A small bike shed: should __noendbr have an alias, like __never_indirect or something, so there is an arch-agnostic way to do this that actually says what it does? (yes, it's in x86-only code now, hence the bike shed...)

-Kees

-- 
Kees Cook