linux-hardening - Re: [GIT PULL] hardening fixes for v6.6-rc3

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Date: Sun, 24 Sep 2023 19:58:31 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [GIT PULL] hardening fixes for v6.6-rc3

On Sat, Sep 23, 2023 at 11:04:57AM -0700, Linus Torvalds wrote:
> On Fri, 22 Sept 2023 at 20:49, Kees Cook <keescook@...omium.org> wrote:
> >
> > 2) __cplusplus is relatively common in UAPI headers already:
> >    $ git grep __cplusplus -- include/uapi | wc -l
> >    58
> 
> Look a bit closer.
> 
> Most of those - by far - is for the usual
> 
>   #if defined(__cplusplus)
>   extern "C" {
>   #endif
> 
> pattern. IOW, it's explicitly not different code, but telling the C++
> compiler that "this is C code".
> 
> So this new #ifdef is an ugly new pattern of "do totally different
> things for C++".
> 
> Apparently required, but very ugly nonetheless.

Most of those in uapi/ are likely unnecessary: extern "C" means
"don't mangle", but kernel doesn't export functions to userspace
except vDSO so there is nothing to mangle in the first place.