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Message-ID: <20240828180129.4046355-1-boqun.feng@gmail.com>
Date: Wed, 28 Aug 2024 11:01:29 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: rust-for-linux@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...sung.com>,
Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>
Subject: [RFC PATCH] rust: Provide correct provenance when constructing THIS_MODULE
Currently while defining `THIS_MODULE` symbol in `module!()`, the
pointer used to contruct `ThisModule` is derived from an immutable
reference of `__this_module`, which means the pointer doesn't have
the provenance for writting, 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@...gle.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
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 571ffa2e189c..aef3b132f32b 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 {{
--
2.45.2
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