Re: [PATCH] x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST

[Alice Ryhl <aliceryhl@google.com>]

On Thu, Apr 10, 2025 at 3:09 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Apr 10, 2025 at 02:45:26PM +0200, Peter Zijlstra wrote:
> > On Thu, Apr 10, 2025 at 02:36:02PM +0200, Peter Zijlstra wrote:
> > > On Thu, Apr 10, 2025 at 11:54:20AM +0000, Paweł Anikiel wrote:
> > > > Calling core::fmt::write() from rust code while FineIBT is enabled
> > > > results in a kernel panic:
>
> > > > This happens because core::fmt::write() calls
> > > > core::fmt::rt::Argument::fmt(), which currently has CFI disabled:
> > > >
> > > > library/core/src/fmt/rt.rs:
> > > > 171     // FIXME: Transmuting formatter in new and indirectly branching to/calling
> > > > 172     // it here is an explicit CFI violation.
> > > > 173     #[allow(inline_no_sanitize)]
> > > > 174     #[no_sanitize(cfi, kcfi)]
> > > > 175     #[inline]
> > > > 176     pub(super) unsafe fn fmt(&self, f: &mut Formatter<'_>) -> Result {
> > > >
>
> Miguel, I cannot find this code in the kernel tree. Is this again
> because Rust is not free-standing and relies on external code?
>
> Can you please fix that. Building against external code that is not
> under our control is a problem.

It's from the core standard library, which is shipped together with
the compiler.

Alice