Re: [PATCH v10 25/27] x86: enable initial Rust support

[Sami Tolvanen]

On Thu, Oct 12, 2023 at 3:47 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxx> wrote:
> > >
> > > On Tue, Oct 11, 2022 at 1:16 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> 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().

I haven't really had time to look into it, so no concrete plans yet.
Adding an attribute shouldn't be terribly difficult, but Kees
expressed interest in automatic salting as well, which might be a more
involved project:

https://github.com/ClangBuiltLinux/linux/issues/1736

Sami