This series is aimed at fixing a soundness issue with how dynamically allocated LockClassKeys are handled. Currently, LockClassKeys can be used without being Pin'd, which can break lockdep since it relies on address stability. Similarly, these keys are not automatically (de)registered with lockdep.
At the suggestion of Alice Ryhl, this series includes a patch for -stable kernels that disables dynamically allocated keys. This prevents backported patches from using the unsound implementation.
Currently, this series requires that all dynamically allocated LockClassKeys have a lifetime of 'static (i.e., they must be leaked after allocation). This is because Lock does not currently keep a reference to the LockClassKey, instead passing it to C via FFI. This causes a problem because the rust compiler would allow creating a 'static Lock with a 'a LockClassKey (with 'a < 'static) while C would expect the LockClassKey to live as long as the lock. This problem represents an avenue for future work.
--- Changes in v3: - Rebased on rust-next - Fixed clippy/compiler warninings (Thanks Boqun Feng) - Link to v2: https://lore.kernel.org/r/20241219-rust-lockdep-v2-0-f65308fbc5ca@gmail.com
Changes in v2: - Dropped formatting change that's already fixed upstream (Thanks Dirk Behme). - Moved safety comment to the right point in the patch series (Thanks Dirk Behme and Boqun Feng). - Added an example of dynamic LockClassKey usage (Thanks Boqun Feng). - Link to v1: https://lore.kernel.org/r/20241004-rust-lockdep-v1-0-e9a5c45721fc@gmail.com
Changes from RFC: - Split into two commits so that dynamically allocated LockClassKeys are removed from stable kernels. (Thanks Alice Ryhl) - Extract calls to C lockdep functions into helpers so things build properly when LOCKDEP=n. (Thanks Benno Lossin) - Remove extraneous `get_ref()` calls. (Thanks Benno Lossin) - Provide better documentation for `new_dynamic()`. (Thanks Benno Lossin) - Ran rustfmt to fix formatting and some extraneous changes. (Thanks Alice Ryhl and Benno Lossin) - Link to RFC: https://lore.kernel.org/r/20240905-rust-lockdep-v1-1-d2c9c21aa8b2@gmail.com
--- Mitchell Levy (2): rust: lockdep: Remove support for dynamically allocated LockClassKeys rust: lockdep: Use Pin for all LockClassKey usages
rust/helpers/helpers.c | 1 + rust/helpers/sync.c | 13 +++++++++ rust/kernel/sync.rs | 63 ++++++++++++++++++++++++++++++++++------- rust/kernel/sync/condvar.rs | 5 ++-- rust/kernel/sync/lock.rs | 9 ++---- rust/kernel/sync/lock/global.rs | 5 ++-- rust/kernel/sync/poll.rs | 2 +- rust/kernel/workqueue.rs | 2 +- 8 files changed, 77 insertions(+), 23 deletions(-) --- base-commit: ceff0757f5dafb5be5205988171809c877b1d3e3 change-id: 20240905-rust-lockdep-d3e30521c8ba
Best regards,
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@metaspac... 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..cb92f2c323e5 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(); + 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 }}; }
On Wed, Feb 5, 2025 at 8:59 PM Mitchell Levy levymitchell0@gmail.com 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@metaspac... Cc: stable@vger.kernel.org Signed-off-by: Mitchell Levy levymitchell0@gmail.com
I imagine we should have:
Fixes: 6ea5aa08857a ("rust: sync: introduce `LockClassKey`")
Is that right?
Thanks!
Cheers, Miguel
On Fri, Feb 07, 2025 at 12:27:58AM +0100, Miguel Ojeda wrote:
On Wed, Feb 5, 2025 at 8:59 PM Mitchell Levy levymitchell0@gmail.com 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@metaspac... Cc: stable@vger.kernel.org Signed-off-by: Mitchell Levy levymitchell0@gmail.com
I imagine we should have:
Fixes: 6ea5aa08857a ("rust: sync: introduce `LockClassKey`")Is that right?
That's correct. Thank you for catching this! I will include this on a resend.
Mitchell
Thanks!
Cheers, Miguel
On 05.02.25 20:59, 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@metaspac... 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(-)
Reviewed-by: Benno Lossin benno.lossin@proton.me
linux-stable-mirror@lists.linaro.org
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Benno Lossin -
Miguel Ojeda -
Mitchell Levy