linux-kernel - Re: [PATCH] x86: Enable IBT in Rust if enabled in C

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Date:   Wed, 11 Oct 2023 19:44:23 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Matthew Maurer <mmaurer@...gle.com>
Cc:     peterz@...radead.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...nel.org>
Subject: Re: [PATCH] x86: Enable IBT in Rust if enabled in C

On Tue, Oct 10, 2023 at 12:43 AM Matthew Maurer <mmaurer@...gle.com> wrote:
>
> These flags are not made conditional on compiler support because at the
> moment exactly one version of rustc supported, and that one supports
> these flags.
>
> Building without these additional flags will manifest as objtool
> printing a large number of errors about missing ENDBR and if CFI is
> enabled (not currently possible) will result in incorrectly structured
> function prefixes.
>
> Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
> ---
>
> Split out the IBT additions as per
> https://lkml.kernel.org/linux-fsdevel/CANiq72kK6ppBE7j=z7uua1cJMKaLoR5U3NUAZXT5MrNEs9ZhfQ@mail.gmail.com/

Thanks a lot Matthew for this! It is great to see those warnings
finally go away.

I have added the `objtool` pass to the intermediate Rust object files
and, with that + this patch applied + IBT enabled (but not
rethunk/retpoline), the only thing I see is:

    samples/rust/rust_print.o: warning: objtool: init_module(): not an
indirect call target
    samples/rust/rust_print.o: warning: objtool: cleanup_module(): not
an indirect call target

But we can fix those independently of this (ideally we want to reuse
the C macros, rather than putting more complexity in `module!`), so:

Acked-by: Miguel Ojeda <ojeda@...nel.org>

I will send the patch for adding `objtool`.

Cheers,
Miguel