Re: [PATCH] closures: CLOSURE_CALLBACK() to fix type punning

From: Kees Cook <keescook@chromium.org>
To: Kent Overstreet <kent.overstreet@linux.dev>
Cc: linux-bcachefs@vger.kernel.org, linux-bcache@vger.kernel.org,
	Coly Li <colyli@suse.de>
Subject: Re: [PATCH] closures: CLOSURE_CALLBACK() to fix type punning
Date: Wed, 29 Nov 2023 12:13:16 -0800	[thread overview]
Message-ID: <202311291212.7955AF30D1@keescook> (raw)
In-Reply-To: <20231120030729.3285278-1-kent.overstreet@linux.dev>

On Sun, Nov 19, 2023 at 10:07:25PM -0500, Kent Overstreet wrote:
> Control flow integrity is now checking that type signatures match on
> indirect function calls. That breaks closures, which embed a work_struct
> in a closure in such a way that a closure_fn may also be used as a
> workqueue fn by the underlying closure code.
> 
> So we have to change closure fns to take a work_struct as their
> argument - but that results in a loss of clarity, as closure fns have
> different semantics from normal workqueue functions (they run owning a
> ref on the closure, which must be released with continue_at() or
> closure_return()).
> 
> Thus, this patc introduces CLOSURE_CALLBACK() and closure_type() macros
> as suggested by Kees, to smooth things over a bit.
> 
> Suggested-by: Kees Cook <keescook@chromium.org>
> Cc: Coly Li <colyli@suse.de>
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Thanks for doing this! This looks reasonable to me. I look forward to
being able to do fancier CFI prototype partitioning in the future...

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

-- 
Kees Cook