Currently while defining `THIS_MODULE` symbol in `module!()`, the pointer used to construct `ThisModule` is derived from an immutable reference of `__this_module`, which means the pointer doesn't have the provenance for writing, and that means any write to that pointer is UB regardless of data races or not. However, the usage of `THIS_MODULE` includes passing this pointer to functions that may write to it (probably in unsafe code), and this will create soundness issues. One way to fix this is using `addr_of_mut!()` but that requires the unstable feature "const_mut_refs". So instead of `addr_of_mut()!`, an extern static `Opaque` is used here: since `Opaque<T>` is transparent to `T`, an extern static `Opaque` will just wrap the C symbol (defined in a C compile unit) in an `Opaque`, which provides a pointer with writable provenance via `Opaque::get()`. This fix the potential UBs because of pointer provenance unmatched. Reported-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> Reviewed-by: Trevor Gross <tmgross@xxxxxxxxx> Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx> Reviewed-by: Gary Guo <gary@xxxxxxxxxxx> Closes: https://rust-for-linux.zulipchat.com/#narrow/stream/x/topic/x/near/465412664 Fixes: 1fbde52bde73 ("rust: add `macros` crate") Cc: stable@xxxxxxxxxxxxxxx # 6.6.x: be2ca1e03965: ("rust: types: Make Opaque::get const") Link: https://lore.kernel.org/r/20240828180129.4046355-1-boqun.feng@xxxxxxxxx [ Fixed two typos, reworded title. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx> diff --git a/rust/macros/module.rs b/rust/macros/module.rs index 411dc103d82e..7a5b899e47b7 100644 --- a/rust/macros/module.rs +++ b/rust/macros/module.rs @@ -217,7 +217,11 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream { // freed until the module is unloaded. #[cfg(MODULE)] static THIS_MODULE: kernel::ThisModule = unsafe {{ - kernel::ThisModule::from_ptr(&kernel::bindings::__this_module as *const _ as *mut _) + extern \"C\" {{ + static __this_module: kernel::types::Opaque<kernel::bindings::module>; + }} + + kernel::ThisModule::from_ptr(__this_module.get()) }}; #[cfg(not(MODULE))] static THIS_MODULE: kernel::ThisModule = unsafe {{
