[PATCH v7 7/7] rust: enable `clippy::ref_as_ptr` lint

Tamir Duberstein
2025-03-25T20:08:01Z

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@proton.me>
Link: https://lore.kernel.org/all/D8PGG7NTWB6U.3SS3A5LN4XWMN@proton.me/
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
Makefile | 1 +
rust/bindings/lib.rs | 1 +
rust/kernel/device_id.rs | 3 ++-
rust/kernel/fs/file.rs | 3 ++-
rust/kernel/str.rs | 4 ++--
rust/kernel/uaccess.rs | 5 +++--
rust/uapi/lib.rs | 1 +
7 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index 2e9eca8b7671..081b5fa2aa81 100644
--- a/Makefile
+++ b/Makefile
@@ -488,6 +488,7 @@ 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 b105a0d899cc..2b69016070c6 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)]
mod bindings_raw {
// Manual definition for blocklisted types.
diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
index 4063f09d76d9..37cc03d1df4c 100644
--- a/rust/kernel/device_id.rs
+++ b/rust/kernel/device_id.rs
@@ -136,7 +136,8 @@ 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()
+ let this: *const Self = self;
+ this.cast()
}

fn id(&self, index: usize) -> &T::RawType {
diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs
index 9e2639aee61a..366e23dc0803 100644
--- a/rust/kernel/fs/file.rs
+++ b/rust/kernel/fs/file.rs
@@ -359,12 +359,13 @@ impl core::ops::Deref for File {
type Target = LocalFile;
#[inline]
fn deref(&self) -> &LocalFile {
+ let this: *const Self = self;
// SAFETY: The caller provides a `&File`, and since it is a reference, it must point at a
// valid file for the desired duration.
//
// 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(this.cast()) }
}
}

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 40034f77fc2f..6233af50bab7 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::mem::transmute::<*const [u8], *const Self>(bytes)) }
}

/// 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::mem::transmute::<*mut [u8], *mut Self>(bytes)) }
}

/// Returns a C pointer to the string.
diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
index 80a9782b1c6e..c042b1fe499e 100644
--- a/rust/kernel/uaccess.rs
+++ b/rust/kernel/uaccess.rs
@@ -242,7 +242,7 @@ 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::mem::transmute::<*mut [u8], *mut [MaybeUninit<u8>]>(out)) };
self.read_raw(out)
}

@@ -348,6 +348,7 @@ pub fn write<T: AsBytes>(&mut self, value: &T) -> Result {
if len > self.length {
return Err(EFAULT);
}
+ let value: *const T = value;
// SAFETY: The reference points to a value of type `T`, so it is valid for reading
// `size_of::<T>()` bytes.
//
@@ -357,7 +358,7 @@ 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>(),
+ value.cast::<c_void>(),
len,
)
};
diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
index d5dab4dfabec..6230ba48201d 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