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

[Benno Lossin <benno.lossin@proton.me>]

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?

> 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?

> 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?

> +mod strict_provenance {
> +    #[doc(hidden)]

Why make them hidden in docs?

> +    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;

> +    }
> +
> +    #[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.

---
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::*;