[tip: locking/core] rust: lockdep: Remove support for dynamically allocated LockClassKeys

["tip-bot2 for Mitchell Levy" <tip-bot2@linutronix.de>]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     5fc1506d33db23894e74caf048ba5591f4986767
Gitweb:        https://git.kernel.org/tip/5fc1506d33db23894e74caf048ba5591f4986767
Author:        Mitchell Levy <levymitchell0@gmail.com>
AuthorDate:    Fri, 07 Feb 2025 16:39:08 -08:00
Committer:     Boqun Feng <boqun.feng@gmail.com>
CommitterDate: Tue, 25 Feb 2025 08:53:08 -08:00

rust: lockdep: Remove support for dynamically allocated LockClassKeys

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
Fixes: 6ea5aa08857a ("rust: sync: introduce `LockClassKey`")
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250207-rust-lockdep-v4-1-7a50a7e88656@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 3498fb3..16eab91 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -30,28 +30,20 @@ pub struct LockClassKey(Opaque<bindings::lock_class_key>);
 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();
+        static CLASS: $crate::sync::LockClassKey =
+            // SAFETY: lockdep expects uninitialized memory when it's handed a statically allocated
+            // lock_class_key
+            unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
         &CLASS
     }};
 }