[PATCH v2 0/2] rust: lockdep: Fix soundness issue affecting LockClassKeys

[PATCH v2 0/2] rust: lockdep: Fix soundness issue affecting LockClassKeys

[Mitchell Levy]

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 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

---
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

---
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        |  3 +-
 8 files changed, 78 insertions(+), 23 deletions(-)
---
base-commit: 0c5928deada15a8d075516e6e0d9ee19011bb000
change-id: 20240905-rust-lockdep-d3e30521c8ba

Best regards,
-- 
Mitchell Levy <levymitchell0@gmail.com>

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

[Mitchell Levy]

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

-- 
2.34.1

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

[kernel test robot]

Hi Mitchell,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 0c5928deada15a8d075516e6e0d9ee19011bb000]

url:    https://github.com/intel-lab-lkp/linux/commits/Mitchell-Levy/rust-lockdep-Remove-support-for-dynamically-allocated-LockClassKeys/20241220-050220
base:   0c5928deada15a8d075516e6e0d9ee19011bb000
patch link:    https://lore.kernel.org/r/20241219-rust-lockdep-v2-1-f65308fbc5ca%40gmail.com
patch subject: [PATCH v2 1/2] rust: lockdep: Remove support for dynamically allocated LockClassKeys
config: x86_64-rhel-9.4-rust (https://download.01.org/0day-ci/archive/20241225/202412251433.T3BhO2CQ-lkp@intel.com/config)
compiler: clang version 19.1.3 (https://github.com/llvm/llvm-project ab51eccf88f5321e7c60591c5546b254b6afab99)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241225/202412251433.T3BhO2CQ-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202412251433.T3BhO2CQ-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> warning: unsafe block missing a safety comment
   --> rust/kernel/sync.rs:45:13
   |
   45  |             unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   ::: rust/kernel/block/mq/gen_disk.rs:111:17
   |
   111 |                 static_lock_class!().as_ptr(),
   |                 -------------------- in this macro invocation
   |
   = help: consider adding a safety comment on the preceding line
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
   = note: requested on the command line with `-W clippy::undocumented-unsafe-blocks`
   = note: this warning originates in the macro `static_lock_class` (in Nightly builds, run with -Z macro-backtrace for more info)
--
>> warning: unsafe block missing a safety comment
   --> rust/kernel/sync.rs:45:13
   |
   45  |             unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   ::: rust/kernel/workqueue.rs:218:21
   |
   218 |             work <- new_work!("Queue::try_spawn"),
   |                     ----------------------------- in this macro invocation
   |
   = help: consider adding a safety comment on the preceding line
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
   = note: this warning originates in the macro `$crate::static_lock_class` which comes from the expansion of the macro `new_work` (in Nightly builds, run with -Z macro-backtrace for more info)

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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

[Boqun Feng]

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
> 

Re: [PATCH v2 0/2] rust: lockdep: Fix soundness issue affecting LockClassKeys

[Boqun Feng]

On Thu, Dec 19, 2024 at 12:58:54PM -0800, Mitchell Levy wrote:
> 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.
> 

Thanks for doing this! I found some clippy warnings with the current
version, but overall it looks good to me. That said, appreciate it if
patch #2 gets more reviews on the interface changes, thanks!

Regards,
Boqun

> ---
> 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
> 
> ---
> 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
> 
> ---
> 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        |  3 +-
>  8 files changed, 78 insertions(+), 23 deletions(-)
> ---
> base-commit: 0c5928deada15a8d075516e6e0d9ee19011bb000
> change-id: 20240905-rust-lockdep-d3e30521c8ba
> 
> Best regards,
> -- 
> Mitchell Levy <levymitchell0@gmail.com>
>