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Date:   Tue, 8 Feb 2022 20:05:46 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Joao Moreira <joao@overdrivepizza.com>
Cc:     Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        hjl.tools@gmail.com, jpoimboe@redhat.com,
        andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org,
        ndesaulniers@google.com, samitolvanen@google.com,
        llvm@lists.linux.dev
Subject: Re: [RFC][PATCH 6/6] objtool: Add IBT validation / fixups
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On Tue, Feb 08, 2022 at 06:21:16PM -0800, Joao Moreira wrote:
> > > 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 :)

Ah, excellent, thanks for the pointers. There's also this in the works:
https://reviews.llvm.org/D119296 (a new CFI mode, designed to play nice
to objtool, IBT, etc.)

-- 
Kees Cook