linux-kernel - Re: [RFC][PATCH 6/6] objtool: Add IBT validation / fixups

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Date:   Tue, 08 Feb 2022 18:21:16 -0800
From:   Joao Moreira <joao@...rdrivepizza.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        hjl.tools@...il.com, jpoimboe@...hat.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, samitolvanen@...gle.com
Subject: Re: [RFC][PATCH 6/6] objtool: Add IBT validation / fixups

>> Note: This feature was already submitted for upstreaming with the
>> llvm-project: https://reviews.llvm.org/D116070
> 
> Ah nice; I see this has been committed now.

Yes, but then some front-end changes also required this fix 
https://reviews.llvm.org/D118052, which is currently under review 
(posting this here in case someone is trying this out).

> 
> Given that IBT will need to work with both Clang and gcc, I suspect the
> objtool approach will still end up needing to do all the verification.
> 
> (And as you say, it has limited visibility into assembly.)

Agreed that at this point objtool provides more coverage. Yet, besides 
being an attempt to relief objtool and improve a bit the compiler 
support as mentioned in the series cover letter, it is still nice to 
reduce the left-over nops and fixups which end-up scattered all around.

FWIIW, https://reviews.llvm.org/D118438 and 
https://reviews.llvm.org/D118355 are also being cooked. Comments and 
ideas for new approaches or improvements in the compiler support for 
this are very welcome :)

Tks,
Joao