Re: [PATCH v4 6/6] rust: use strict provenance APIs

Tamir Duberstein
2025-03-17T10:53:57Z

On Mon, Mar 17, 2025 at 5:34 AM Benno Lossin <benno.lossin@proton.me> wrote:
>
> On Sat Mar 15, 2025 at 1:17 PM CET, Tamir Duberstein wrote:
> > Throughout the tree, use the strict provenance APIs stabilized in Rust
> > 1.84.0[1]. Retain backwards-compatibility by introducing forwarding
> > functions at the `kernel` crate root along with polyfills for rustc <
> > 1.84.0.
> >
> > Use `#[allow(clippy::incompatible_msrv)]` to avoid warnings on rustc <
> > 1.84.0 as our MSRV is 1.78.0.
>
> This isn't necessary, right?

It is necessary. MSRV is encoded in .clippy.toml, it doesn't matter
what the *current* rustc version is.

> > In the `kernel` crate, enable the strict provenance lints on rustc >=
> > 1.84.0; do this in `lib.rs` rather than `Makefile` to avoid introducing
> > compiler flags that are dependent on the rustc version in use.
>
> So it won't be enabled in the doctests, right?

Yes, that is correct.

> > Link: https://blog.rust-lang.org/2025/01/09/Rust-1.84.0.html#strict-provenance-apis [1]
> > Suggested-by: Benno Lossin <benno.lossin@proton.me>
> > Link: https://lore.kernel.org/all/D8EIXDMRXMJP.36TFCGWZBRS3Y@proton.me/
> > Signed-off-by: Tamir Duberstein <tamird@gmail.com>
> > ---
> > init/Kconfig | 3 +++
> > rust/kernel/alloc.rs | 2 +-
> > rust/kernel/devres.rs | 4 ++--
> > rust/kernel/io.rs | 14 +++++++-------
> > rust/kernel/lib.rs | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
> > rust/kernel/of.rs | 2 +-
> > rust/kernel/pci.rs | 4 ++--
> > rust/kernel/str.rs | 16 ++++++----------
> > rust/kernel/uaccess.rs | 12 ++++++++----
> > 9 files changed, 82 insertions(+), 27 deletions(-)
>
>
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index 486715528587..84eb2602e79e 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -17,6 +17,9 @@
> > #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(coerce_unsized))]
> > #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(dispatch_from_dyn))]
> > #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(unsize))]
> > +#![cfg_attr(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE, feature(strict_provenance_lints))]
> > +#![cfg_attr(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE, deny(fuzzy_provenance_casts))]
> > +#![cfg_attr(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE, deny(lossy_provenance_casts))]
> > #![feature(inline_const)]
> > #![feature(lint_reasons)]
> > // Stable in Rust 1.83
> > @@ -25,6 +28,55 @@
> > #![feature(const_ptr_write)]
> > #![feature(const_refs_to_cell)]
> >
> > +#[cfg(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE)]
> > +#[allow(clippy::incompatible_msrv)]
>
> Do we still need this allow?

Yes, explained above.

> > +mod strict_provenance {
> > + #[doc(hidden)]
>
> Why make them hidden in docs?

I've added documentation that defers to the standard library.

>
> > + pub fn expose_provenance<T>(addr: *const T) -> usize {
> > + addr.expose_provenance()
>
> Instead of having these stubs here, you can probably just do
>
> pub use core::ptr::expose_provenance;

This doesn't work for the methods on primitives, but it works for the
free functions. Done.

> > + }
> > +
> > + #[doc(hidden)]
> > + pub fn without_provenance_mut<T>(addr: usize) -> *mut T {
> > + core::ptr::without_provenance_mut(addr)
> > + }
> > +
> > + #[doc(hidden)]
> > + pub fn with_exposed_provenance<T>(addr: usize) -> *const T {
> > + core::ptr::with_exposed_provenance(addr)
> > + }
> > +
> > + #[doc(hidden)]
> > + pub fn with_exposed_provenance_mut<T>(addr: usize) -> *mut T {
> > + core::ptr::with_exposed_provenance_mut(addr)
> > + }
> > +}
> > +
> > +#[cfg(not(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE))]
> > +mod strict_provenance {
> > + #[doc(hidden)]
>
> I think we should document these.

Done.

>
> ---
> Cheers,
> Benno
>
> > + pub fn expose_provenance<T>(addr: *const T) -> usize {
> > + addr.cast::<()>() as usize
> > + }
> > +
> > + #[doc(hidden)]
> > + pub fn without_provenance_mut<T>(addr: usize) -> *mut T {
> > + addr as *mut T
> > + }
> > +
> > + #[doc(hidden)]
> > + pub fn with_exposed_provenance<T>(addr: usize) -> *const T {
> > + addr as *const T
> > + }
> > +
> > + #[doc(hidden)]
> > + pub fn with_exposed_provenance_mut<T>(addr: usize) -> *mut T {
> > + addr as *mut T
> > + }
> > +}
> > +
> > +pub use strict_provenance::*;
>