linux-kernel - [PATCH v2 5/5] rust: types: implement `ForeignOwnable` for `Arc<T>`

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230130064404.744600-5-wedsonaf@gmail.com>
Date:   Mon, 30 Jan 2023 03:44:04 -0300
From:   Wedson Almeida Filho <wedsonaf@...il.com>
To:     rust-for-linux@...r.kernel.org
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        linux-kernel@...r.kernel.org,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Vincenzo Palazzo <vincenzopalazzodev@...il.com>,
        Alice Ferrazzi <alice.ferrazzi@...aclelinux.com>
Subject: [PATCH v2 5/5] rust: types: implement `ForeignOwnable` for `Arc<T>`

This allows us to hand ownership of Rust ref-counted objects to
the C side of the kernel.

Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>
Reviewed-by: Gary Guo <gary@...yguo.net>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@...il.com>
Reviewed-by: Alice Ferrazzi <alice.ferrazzi@...aclelinux.com>
---
v1 -> v2: Unmodified

 rust/kernel/sync/arc.rs | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index ff73f9240ca1..519a6ec43644 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -15,7 +15,11 @@
 //!
 //! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
 
-use crate::{bindings, error::Result, types::Opaque};
+use crate::{
+    bindings,
+    error::Result,
+    types::{ForeignOwnable, Opaque},
+};
 use alloc::boxed::Box;
 use core::{
     marker::{PhantomData, Unsize},
@@ -189,6 +193,32 @@ impl<T: ?Sized> Arc<T> {
     }
 }
 
+impl<T: 'static> ForeignOwnable for Arc<T> {
+    type Borrowed<'a> = ArcBorrow<'a, T>;
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        ManuallyDrop::new(self).ptr.as_ptr() as _
+    }
+
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
+        // SAFETY: By the safety requirement of this function, we know that `ptr` came from
+        // a previous call to `Arc::into_foreign`.
+        let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
+
+        // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
+        // for the lifetime of the returned value. Additionally, the safety requirements of
+        // `ForeignOwnable::borrow_mut` ensure that no new mutable references are created.
+        unsafe { ArcBorrow::new(inner) }
+    }
+
+    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
+        // SAFETY: By the safety requirement of this function, we know that `ptr` came from
+        // a previous call to `Arc::into_foreign`, which owned guarantees that `ptr` is valid and
+        // owns a reference.
+        unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
+    }
+}
+
 impl<T: ?Sized> Deref for Arc<T> {
     type Target = T;
 
-- 
2.34.1