[PATCH v11 6/6] rust: enable `clippy::ref_as_ptr` lint

[Tamir Duberstein]

In Rust 1.78.0, Clippy introduced the `ref_as_ptr` lint [1]:

> Using `as` casts may result in silently changing mutability or type.

While this doesn't eliminate unchecked `as` conversions, it makes such
conversions easier to scrutinize.  It also has the slight benefit of
removing a degree of freedom on which to bikeshed. Thus apply the
changes and enable the lint -- no functional change intended.

Link: https://rust-lang.github.io/rust-clippy/master/index.html#ref_as_ptr [1]
Suggested-by: Benno Lossin <benno.lossin at proton.me>
Link: https://lore.kernel.org/all/D8PGG7NTWB6U.3SS3A5LN4XWMN@proton.me/
Reviewed-by: Benno Lossin <benno.lossin at proton.me>
Reviewed-by: Boqun Feng <boqun.feng at gmail.com>
Signed-off-by: Tamir Duberstein <tamird at gmail.com>
---
 Makefile                 | 1 +
 rust/bindings/lib.rs     | 1 +
 rust/kernel/device_id.rs | 2 +-
 rust/kernel/fs/file.rs   | 2 +-
 rust/kernel/str.rs       | 4 ++--
 rust/kernel/uaccess.rs   | 4 ++--
 rust/uapi/lib.rs         | 1 +
 7 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index 29cf39be14de..1a855f42a34a 100644
--- a/Makefile
+++ b/Makefile
@@ -489,6 +489,7 @@ export rust_common_flags := --edition=2021 \
 			    -Wclippy::no_mangle_with_rust_abi \
 			    -Wclippy::ptr_as_ptr \
 			    -Wclippy::ptr_cast_constness \
+			    -Wclippy::ref_as_ptr \
 			    -Wclippy::undocumented_unsafe_blocks \
 			    -Wclippy::unnecessary_safety_comment \
 			    -Wclippy::unnecessary_safety_doc \
diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
index 7631c9f6708d..474cc98c48a3 100644
--- a/rust/bindings/lib.rs
+++ b/rust/bindings/lib.rs
@@ -27,6 +27,7 @@
 #[allow(dead_code)]
 #[allow(clippy::cast_lossless)]
 #[allow(clippy::ptr_as_ptr)]
+#[allow(clippy::ref_as_ptr)]
 #[allow(clippy::undocumented_unsafe_blocks)]
 #[cfg_attr(CONFIG_RUSTC_HAS_UNNECESSARY_TRANSMUTES, allow(unnecessary_transmutes))]
 mod bindings_raw {
diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
index f9d55ac7b9e6..3dc72ca8cfc2 100644
--- a/rust/kernel/device_id.rs
+++ b/rust/kernel/device_id.rs
@@ -136,7 +136,7 @@ impl<T: RawDeviceId, U, const N: usize> IdTable<T, U> for IdArray<T, U, N> {
     fn as_ptr(&self) -> *const T::RawType {
         // This cannot be `self.ids.as_ptr()`, as the return pointer must have correct provenance
         // to access the sentinel.
-        (self as *const Self).cast()
+        core::ptr::from_ref(self).cast()
     }
 
     fn id(&self, index: usize) -> &T::RawType {
diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs
index e9bfbad00755..35fd5db35c46 100644
--- a/rust/kernel/fs/file.rs
+++ b/rust/kernel/fs/file.rs
@@ -366,7 +366,7 @@ fn deref(&self) -> &LocalFile {
         //
         // By the type invariants, there are no `fdget_pos` calls that did not take the
         // `f_pos_lock` mutex.
-        unsafe { LocalFile::from_raw_file((self as *const Self).cast()) }
+        unsafe { LocalFile::from_raw_file(core::ptr::from_ref(self).cast()) }
     }
 }
 
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 43597eb7c5c1..cbc8b459ed41 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -29,7 +29,7 @@ pub const fn is_empty(&self) -> bool {
     #[inline]
     pub const fn from_bytes(bytes: &[u8]) -> &Self {
         // SAFETY: `BStr` is transparent to `[u8]`.
-        unsafe { &*(bytes as *const [u8] as *const BStr) }
+        unsafe { &*(core::ptr::from_ref(bytes) as *const BStr) }
     }
 
     /// Strip a prefix from `self`. Delegates to [`slice::strip_prefix`].
@@ -290,7 +290,7 @@ pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError
     #[inline]
     pub unsafe fn from_bytes_with_nul_unchecked_mut(bytes: &mut [u8]) -> &mut CStr {
         // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
-        unsafe { &mut *(bytes as *mut [u8] as *mut CStr) }
+        unsafe { &mut *(core::ptr::from_mut(bytes) as *mut CStr) }
     }
 
     /// Returns a C pointer to the string.
diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
index 6d70edd8086a..4ef13cf13a78 100644
--- a/rust/kernel/uaccess.rs
+++ b/rust/kernel/uaccess.rs
@@ -240,7 +240,7 @@ pub fn read_raw(&mut self, out: &mut [MaybeUninit<u8>]) -> Result {
     pub fn read_slice(&mut self, out: &mut [u8]) -> Result {
         // SAFETY: The types are compatible and `read_raw` doesn't write uninitialized bytes to
         // `out`.
-        let out = unsafe { &mut *(out as *mut [u8] as *mut [MaybeUninit<u8>]) };
+        let out = unsafe { &mut *(core::ptr::from_mut(out) as *mut [MaybeUninit<u8>]) };
         self.read_raw(out)
     }
 
@@ -355,7 +355,7 @@ pub fn write<T: AsBytes>(&mut self, value: &T) -> Result {
         let res = unsafe {
             bindings::_copy_to_user(
                 self.ptr as *mut c_void,
-                (value as *const T).cast::<c_void>(),
+                core::ptr::from_ref(value).cast::<c_void>(),
                 len,
             )
         };
diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
index 08e68ebef606..31c2f713313f 100644
--- a/rust/uapi/lib.rs
+++ b/rust/uapi/lib.rs
@@ -16,6 +16,7 @@
     clippy::all,
     clippy::cast_lossless,
     clippy::ptr_as_ptr,
+    clippy::ref_as_ptr,
     clippy::undocumented_unsafe_blocks,
     dead_code,
     missing_docs,

-- 
2.49.0