commit a5a3c952e82c1ada12bf8c55b73af26f1a454bd2 upstream.
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@google.com Signed-off-by: Boqun Feng boqun.feng@gmail.com Reviewed-by: Alice Ryhl aliceryhl@google.com Reviewed-by: Trevor Gross tmgross@umich.edu Reviewed-by: Benno Lossin benno.lossin@proton.me Reviewed-by: Gary Guo gary@garyguo.net Closes: https://rust-for-linux.zulipchat.com/#narrow/stream/x/topic/x/near/465412664 Fixes: 1fbde52bde73 ("rust: add `macros` crate") Cc: stable@vger.kernel.org # 6.6.x: be2ca1e03965: ("rust: types: Make Opaque::get const") Link: https://lore.kernel.org/r/20240828180129.4046355-1-boqun.feng@gmail.com [ Fixed two typos, reworded title. - Miguel ] Signed-off-by: Miguel Ojeda ojeda@kernel.org [ Boqun: Use `UnsafeCell` since `Opaque` is not in v6.1, as suggested by Gary Guo, `UnsafeCell` also suffices for this particular case because `__this_module` is only used to create `THIS_MODULE`, no other Rust code will touch it. ] Signed-off-by: Boqun Feng boqun.feng@gmail.com --- Backports for 6.6+ are already done automatically, we have to do a special backport for 6.1 because of lacking an API.
I've tested it on x86 with the rust_minimal module based on 6.1.112
rust/macros/module.rs | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/rust/macros/module.rs b/rust/macros/module.rs index 031028b3dc41..94a92ab82b6b 100644 --- a/rust/macros/module.rs +++ b/rust/macros/module.rs @@ -183,7 +183,11 @@ 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: core::cell::UnsafeCellkernel::bindings::module; + }} + + kernel::ThisModule::from_ptr(__this_module.get()) }}; #[cfg(not(MODULE))] static THIS_MODULE: kernel::ThisModule = unsafe {{