linux-kernel - Re: [PATCH v1] rust: cfi: only 64-bit arm and x86 support CFI

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Message-ID: <CAH5fLghqe8sxLD3vk6VLbA8UoMgEw1iNxgE8uETAeCnRz1D0DQ@mail.gmail.com>
Date: Mon, 8 Sep 2025 15:19:02 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Conor Dooley <conor@...nel.org>
Cc: linux-kernel@...r.kernel.org, Conor Dooley <conor.dooley@...rochip.com>, 
	stable@...r.kernel.org, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Alexandre Ghiti <alex@...ti.fr>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, Kees Cook <kees@...nel.org>, 
	Sami Tolvanen <samitolvanen@...gle.com>, Matthew Maurer <mmaurer@...gle.com>, 
	"Peter Zijlstra (Intel)" <peterz@...radead.org>, linux-riscv@...ts.infradead.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v1] rust: cfi: only 64-bit arm and x86 support CFI_CLANG

On Mon, Sep 8, 2025 at 3:13 PM Conor Dooley <conor@...nel.org> wrote:
>
> From: Conor Dooley <conor.dooley@...rochip.com>
>
> The kernel uses the standard rustc targets for non-x86 targets, and out
> of those only 64-bit arm's target has kcfi support enabled. For x86, the
> custom 64-bit target enables kcfi.
>
> The HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC config option that allows
> CFI_CLANG to be used in combination with RUST does not check whether the
> rustc target supports kcfi. This breaks the build on riscv (and
> presumably 32-bit arm) when CFI_CLANG and RUST are enabled at the same
> time.
>
> Ordinarily, a rustc-option check would be used to detect target support
> but unfortunately rustc-option filters out the target for reasons given
> in commit 46e24a545cdb4 ("rust: kasan/kbuild: fix missing flags on first
> build"). As a result, if the host supports kcfi but the target does not,
> e.g. when building for riscv on x86_64, the build would remain broken.
>
> Instead, make HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC depend on the only
> two architectures where the target used supports it to fix the build.
>
> CC: stable@...r.kernel.org
> Fixes: ca627e636551e ("rust: cfi: add support for CFI_CLANG with Rust")
> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>