linux-kernel - Re: [PATCH] x86/Kconfig: make CFI_AUTO

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Message-ID: <20250410140850.GH9833@noisy.programming.kicks-ass.net>
Date: Thu, 10 Apr 2025 16:08:50 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Paweł Anikiel <panikiel@...gle.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Kees Cook <kees@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nathan Chancellor <nathan@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	Matthew Maurer <mmaurer@...gle.com>,
	Ramon de C Valle <rcvalle@...gle.com>
Subject: Re: [PATCH] x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST

On Thu, Apr 10, 2025 at 03:59:53PM +0200, Alice Ryhl wrote:
> On Thu, Apr 10, 2025 at 3:34 PM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Thu, Apr 10, 2025 at 03:27:55PM +0200, Miguel Ojeda wrote:
> > > On Thu, Apr 10, 2025 at 3:26 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > > >
> > > > New compiler can't build old core?
> > >
> > > No, that is not intended to work -- `core` is tied to the compiler.
> >
> > OMFG, you just gave me another reason to hate on this rust-bucket of a
> > language :-/ What language can't even build an old version of its own
> > runtime :-(
> 
> I don't think there's anything unreasonable about having a place to
> put logic that depends on compiler internals.

Having compiler internals exposed to such an extend that programs can
make use of them _is_ weird. It creates the whole problem of where to
put it.

C++ doesn't have anything like this afaik. Esp. if you disable rtti and
exception muck, you get a very minimal runtime. And even if you don't,
it certainly doesn't break every 6 weeks. ABIs and all that.

Maybe I've been living in C/C++ land for too long, but you either expose
a full language feature and then everybody can use it, runtime,
libraries and user code alike, or you don't.

> > Anyway, given this core nonsense is now CFI unsound, it is no longer
> > suitable to build the kernel. So either refrain from using part of the
> > core that trips this, or get it fixed asap.
> 
> I submitted a PR that I believe should fix it:
> https://github.com/rust-lang/rust/pull/139632

Thanks!