[Cc Sasha]

On Sun, Sep 08, 2024 at 01:26:32PM +0200, gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x a5a3c952e82c1ada12bf8c55b73af26f1a454bd2 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024090831-camera-backlands-a643@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

a5a3c952e82c ("rust: macros: provide correct provenance when constructing THIS_MODULE")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a5a3c952e82c1ada12bf8c55b73af26f1a454bd2 Mon Sep 17 00:00:00 2001 From: Boqun Feng boqun.feng@gmail.com Date: Wed, 28 Aug 2024 11:01:29 -0700 Subject: [PATCH] rust: macros: provide correct provenance when constructing THIS_MODULE

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

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>;
  

As Gary mentioned:

https://lore.kernel.org/stable/20240910105557.7ada99d1.gary@garyguo.net/

`Opaque` doesn't exist in 6.1. We could use `UnsafeCell` here to replace `Opaque`. I will send a backport patch later today if needed.

Regards, Boqun

•            }}
  

•            kernel::ThisModule::from_ptr(__this_module.get())
         }};
         #[cfg(not(MODULE))]
         static THIS_MODULE: kernel::ThisModule = unsafe {{