linux-kernel - [PATCH locking 10/11] rust: lockdep: Remove support for dynamically allocated LockClassKeys

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Message-ID: <20250307232717.1759087-11-boqun.feng@gmail.com>
Date: Fri,  7 Mar 2025 15:27:00 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>,
	linux-kernel@...r.kernel.org,
	Mitchell Levy <levymitchell0@...il.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	stable@...r.kernel.org,
	Benno Lossin <benno.lossin@...ton.me>,
	Boqun Feng <boqun.feng@...il.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	Lyude Paul <lyude@...hat.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Martin Rodriguez Reboredo <yakoyoku@...il.com>,
	rust-for-linux@...r.kernel.org (open list:RUST)
Subject: [PATCH locking 10/11] rust: lockdep: Remove support for dynamically allocated LockClassKeys

From: Mitchell Levy <levymitchell0@...il.com>

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@...gle.com>
Link: https://lore.kernel.org/rust-for-linux/20240815074519.2684107-3-nmi@metaspace.dk/
Cc: stable@...r.kernel.org
Fixes: 6ea5aa08857a ("rust: sync: introduce `LockClassKey`")
Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
Signed-off-by: Mitchell Levy <levymitchell0@...il.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.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 3498fb344dc9..16eab9138b2b 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -30,28 +30,20 @@
 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();
+        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
     }};
 }
-- 
2.47.1