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

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Message-Id: <20241219-rust-lockdep-v2-1-f65308fbc5ca@gmail.com>
Date: Thu, 19 Dec 2024 12:58:55 -0800
From: Mitchell Levy <levymitchell0@...il.com>
To: Boqun Feng <boqun.feng@...il.com>, Miguel Ojeda <ojeda@...nel.org>, 
 Alex Gaynor <alex.gaynor@...il.com>, 
 Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <benno.lossin@...ton.me>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>, Andreas Hindborg <a.hindborg@...nel.org>, 
 Andreas Hindborg <a.hindborg@...nel.org>
Cc: linux-block@...r.kernel.org, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Mitchell Levy <levymitchell0@...il.com>
Subject: [PATCH v2 1/2] 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@...gle.com>
Link: https://lore.kernel.org/rust-for-linux/20240815074519.2684107-3-nmi@metaspace.dk/
Cc: stable@...r.kernel.org
Signed-off-by: Mitchell Levy <levymitchell0@...il.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 =
+            unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
         &CLASS
     }};
 }

-- 
2.34.1