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

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Message-ID: <20250416202040.GD38216@noisy.programming.kicks-ass.net>
Date: Wed, 16 Apr 2025 22:20:40 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Alice Ryhl <aliceryhl@...gle.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 Tue, Apr 15, 2025 at 05:15:31PM +0200, Miguel Ojeda wrote:
> On Thu, Apr 10, 2025 at 4:00 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > I submitted a PR that I believe should fix it:
> > https://github.com/rust-lang/rust/pull/139632
> 
> This landed, scheduled for Rust 1.88 (2025-06-26) if all goes well.
> 
> Peter: are you OK with landing a patch like this? Well, modified to
> look like this now that we know the version:
> 
>     depends on FINEIBT
>     depends on !RUST || RUSTC_VERSION >= 108800
> 
> (assuming we confirm the nightly build works properly)

I don't much like it -- disabling FineIBT at config time like this also
kills the CFI type rehash. Not to mention that FineIBT is a Spectre-BHI
mitigation, esp. with that arity thing on top.

I don't suppose we can simply mandate this rust version?

Speaking of which, I should go install this latest rust thing....