On Tue, Sep 10, 2024 at 12:12 PM Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > 6.1-stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Boqun Feng <boqun.feng@xxxxxxxxx> > > [ Upstream commit a5a3c952e82c1ada12bf8c55b73af26f1a454bd2 ] > > 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> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> The opaque type doesn't exist yet on 6.1, so this needs to be changed for the 6.1 backport. It won't compile as-is. > --- > 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..071b96639a2e 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: kernel::types::Opaque<kernel::bindings::module>; > + }} > + > + kernel::ThisModule::from_ptr(__this_module.get()) > }}; > #[cfg(not(MODULE))] > static THIS_MODULE: kernel::ThisModule = unsafe {{ > -- > 2.43.0 > > >
