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Date:   Thu, 12 Oct 2023 12:47:41 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.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>,
        =?iso-8859-1?Q?Bj=F6rn?= 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
Subject: Re: [PATCH v10 25/27] x86: enable initial Rust support
Message-ID: <20231012104741.GN6307@noisy.programming.kicks-ass.net>
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On Fri, Oct 14, 2022 at 11:34:30AM -0700, Sami Tolvanen wrote:
> On Fri, Oct 14, 2022 at 11:05 AM Miguel Ojeda
> <miguel.ojeda.sandonis@gmail.com> wrote:
> >
> > On Tue, Oct 11, 2022 at 1:16 AM Sami Tolvanen <samitolvanen@google.com> wrote:
> > >
> > > Rust supports IBT with -Z cf-protection=branch, but I don't see this
> > > option being enabled in the kernel yet. Cross-language CFI is going to
> > > require a lot more work though because the type systems are not quite
> > > compatible:
> > >
> > > https://github.com/rust-lang/rfcs/pull/3296
> >
> > I have pinged Ramon de C Valle as he is the author of the RFC above
> > and implementation work too; since a month or so ago he also leads the
> > Exploit Mitigations Project Group in Rust.
> 
> Thanks, Miguel. I also talked to Ramon about KCFI earlier this week
> and he expressed interest in helping with rustc support for it. In the
> meanwhile, I think we can just add a depends on !CFI_CLANG to avoid
> issues here.

Having just read up on the thing it looks like the KCFI thing is
resolved.

I'm not sure I understand most of the objections in that thread through
-- enabling CFI *will* break stuff, so what.

Squashing the integer types seems a workable compromise I suppose. One
thing that's been floated in the past is adding a 'seed' attribute to
some functions in order to distinguish functions of otherwise identical
signature.

The Rust thing would then also need to support this attribute.

Are there any concrete plans for this? It would allow, for example,
to differentiate address_space_operations::swap_deactivate() from any
other random function that takes only a file argument, say:
locks_remove_file().