Re: [PATCH v2 1/2] rust: lockdep: Remove support for dynamically allocated LockClassKeys

[Boqun Feng <boqun.feng@gmail.com>]

On Thu, Dec 19, 2024 at 12:58:55PM -0800, Mitchell Levy wrote:
> Currently, dynamically allocated LockCLassKeys can be used from the Rust
> side without having them registered. This is a soundness issue, so
> remove them.
> 
> Suggested-by: Alice Ryhl <aliceryhl@google.com>
> Link: https://lore.kernel.org/rust-for-linux/20240815074519.2684107-3-nmi@metaspace.dk/
> Cc: stable@vger.kernel.org
> Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
> ---
>  rust/kernel/sync.rs | 16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
> 
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 1eab7ebf25fd..ae16bfd98de2 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -29,28 +29,20 @@
>  unsafe impl Sync for LockClassKey {}
>  
>  impl LockClassKey {
> -    /// Creates a new lock class key.
> -    pub const fn new() -> Self {
> -        Self(Opaque::uninit())
> -    }
> -
>      pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
>          self.0.get()
>      }
>  }
>  
> -impl Default for LockClassKey {
> -    fn default() -> Self {
> -        Self::new()
> -    }
> -}
> -
>  /// Defines a new static lock class and returns a pointer to it.
>  #[doc(hidden)]
>  #[macro_export]
>  macro_rules! static_lock_class {
>      () => {{
> -        static CLASS: $crate::sync::LockClassKey = $crate::sync::LockClassKey::new();
> +        // SAFETY: lockdep expects uninitialized memory when it's handed a statically allocated
> +        // lock_class_key
> +        static CLASS: $crate::sync::LockClassKey =

About the clippy warning reported by 0day, I think you could resolve
that by moving the above safety comment here.

Regards,
Boqun

> +            unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
>          &CLASS
>      }};
>  }
> 
> -- 
> 2.34.1
>