Re: FAILED: patch "[PATCH] rust: macros: provide correct provenance when constructing" failed to apply to 6.1-stable tree

[Boqun Feng <boqun.feng@gmail.com>]

[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 {{
>