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

[Kees Cook]

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