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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Mon, 9 Oct 2023 18:31:13 +0200
Message-ID: <CANiq72kK6ppBE7j=z7uua1cJMKaLoR5U3NUAZXT5MrNEs9ZhfQ@mail.gmail.com>
Subject: Re: [PATCH v10 25/27] x86: enable initial Rust support
To:     Matthew Maurer <mmaurer@google.com>
Cc:     Sami Tolvanen <samitolvanen@google.com>,
        Peter Zijlstra <peterz@infradead.org>, rcvalle@google.com,
        Miguel Ojeda <ojeda@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, patches@lists.linux.dev,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@google.com>,
        David Gow <davidgow@google.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-doc@vger.kernel.org
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On Mon, Oct 9, 2023 at 6:01=E2=80=AFPM Matthew Maurer <mmaurer@google.com> =
wrote:
>
> If the IBT part would be helpful by itself immediately, I can split
> that out - it's only the KCFI portion that won't currently work.

Thanks Matthew. I don't think we are in a rush, but if it is not too
much work to split it, that would be great, instead of adding the
restriction.

For retthunk, by the way, I forgot to mention to Greg above that (in
the original discussion with PeterZ) that I did a quick test back then
to hack the equivalent of `-mfunction-return=3Dthunk-extern` into
`rustc` to show that the compiler could use it via LLVM (by passing
the attribute in the IR). At least at a basic level it seemed to work:
I got a userspace program to count the times that it went through the
return thunk. I didn't try to do anything on the kernel side, but at
least for the compiler side, it seemed OK. So it may be way easier (on
the compiler side) than the CFI work?

Cheers,
Miguel