rust: use strict provenance on rustc >= 1.84.0

Rust 1.84.0 stabilized the strict provenance APIs[1].

This patch enables the (unstable) lints `fuzzy_provenance_casts` and
`lossy_provenance_casts` (available since Rust 1.61.0[2]) and uses
strict provenance APIs where these lints triggered. The `kernel` crate
is kept backwards-compatible by introducing forwarding functions at the
root which are marked `#[allow(clippy::incompatible_msrv)]` to avoid
warnings on rustc < 1.84.0.

The discussion in the tracking Issue for strict_provenance_lints[3]
seems to be nearing resolution with the only open question being:

> do we really want two separate lints for the two directions?

which seems minor enough that this is unlikely to cause significant
churn when stabilized.

This is limited to the `kernel` crate because adding these lints in the
root `Makefile` causes `core` itself to be compiled with them, which in
turn causes warnings on the implementations of the strict provenance
APIs themselves.

Link: https://blog.rust-lang.org/2025/01/09/Rust-1.84.0.html#strict-provenance-apis [1]
Link: https://github.com/rust-lang/rust/blob/e71f9a9a98b0faf423844bf0ba7438f29dc27d58/compiler/rustc_feature/src/unstable.rs#L605 [2]
Link: rust-lang/rust#130351 [3]
Suggested-by: Benno Lossin <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/

Author: tamird

Makefile

@@ -473,6 +473,8 @@ export rust_common_flags := --edition=2021 \
 			    -Astable_features \
 			    -Dnon_ascii_idents \
 			    -Dunsafe_op_in_unsafe_fn \
+			    -Wfuzzy_provenance_casts \
+			    -Wlossy_provenance_casts \
 			    -Wmissing_docs \
 			    -Wrust_2018_idioms \
 			    -Wunreachable_pub \
@@ -498,7 +500,7 @@ KBUILD_HOSTCFLAGS   := $(KBUILD_USERHOSTCFLAGS) $(HOST_LFS_CFLAGS) \
 KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS) \
 		       -I $(srctree)/scripts/include
 KBUILD_HOSTRUSTFLAGS := $(rust_common_flags) -O -Cstrip=debuginfo \
-			-Zallow-features= $(HOSTRUSTFLAGS)
+			$(HOSTRUSTFLAGS)
 KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
 KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 KBUILD_PROCMACROLDFLAGS := $(or $(PROCMACROLDFLAGS),$(KBUILD_HOSTLDFLAGS))
@@ -870,6 +872,11 @@ KBUILD_CFLAGS += -Os
 KBUILD_RUSTFLAGS += -Copt-level=s
 endif
 
+# Lints were moved to `strict_provenance_lints` when `strict_provenance` was stabilized.
+#
+# See https://github.com/rust-lang/rust/commit/56ee492a6e7a917b2b3f888e33dd52a13d3ecb64.
+export rustc_strict_provenance_feature := $(if $(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE),strict_provenance_lints,strict_provenance)
+
 # Always set `debug-assertions` and `overflow-checks` because their default
 # depends on `opt-level` and `debug-assertions`, respectively.
 KBUILD_RUSTFLAGS += -Cdebug-assertions=$(if $(CONFIG_RUST_DEBUG_ASSERTIONS),y,n)

init/Kconfig

@@ -132,6 +132,9 @@ config CC_HAS_COUNTED_BY
 config RUSTC_HAS_COERCE_POINTEE
 	def_bool RUSTC_VERSION >= 108400
 
+config RUSTC_HAS_STABLE_STRICT_PROVENANCE
+	def_bool RUSTC_VERSION >= 108400
+
 config PAHOLE_VERSION
 	int
 	default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))

rust/Makefile

@@ -57,10 +57,12 @@ endif
 core-cfgs = \
     --cfg no_fp_fmt_parse
 
+rustc_strict_provenance_flags = -Zcrate-attr='feature($(rustc_strict_provenance_feature))'
+
 quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
       cmd_rustdoc = \
 	OBJTREE=$(abspath $(objtree)) \
-	$(RUSTDOC) $(filter-out $(skip_flags),$(if $(rustdoc_host),$(rust_common_flags),$(rust_flags))) \
+	$(RUSTDOC) $(filter-out $(skip_flags),$(if $(rustdoc_host),$(rust_common_flags),$(rust_flags)) $(rustc_strict_provenance_flags)) \
 		$(rustc_target_flags) -L$(objtree)/$(obj) \
 		-Zunstable-options --generate-link-to-definition \
 		--output $(rustdoc_output) \
@@ -99,7 +101,7 @@ rustdoc-macros: $(src)/macros/lib.rs FORCE
 
 # Starting with Rust 1.82.0, skipping `-Wrustdoc::unescaped_backticks` should
 # not be needed -- see https://github.com/rust-lang/rust/pull/128307.
-rustdoc-core: private skip_flags = -Wrustdoc::unescaped_backticks
+rustdoc-core: private skip_flags = -Wrustdoc::unescaped_backticks $(rustc_strict_provenance_flags)
 rustdoc-core: private rustc_target_flags = $(core-cfgs)
 rustdoc-core: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
 	+$(call if_changed,rustdoc)
@@ -122,6 +124,7 @@ quiet_cmd_rustc_test_library = $(RUSTC_OR_CLIPPY_QUIET) TL $<
       cmd_rustc_test_library = \
 	OBJTREE=$(abspath $(objtree)) \
 	$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
+		$(rustc_strict_provenance_flags) \
 		@$(objtree)/include/generated/rustc_cfg $(rustc_target_flags) \
 		--crate-type $(if $(rustc_test_library_proc),proc-macro,rlib) \
 		--out-dir $(objtree)/$(obj)/test --cfg testlib \
@@ -155,11 +158,19 @@ rusttestlib-uapi: private rustc_target_flags = --extern ffi
 rusttestlib-uapi: $(src)/uapi/lib.rs rusttestlib-ffi FORCE
 	+$(call if_changed,rustc_test_library)
 
+# `rustdoc --test` doesn't respect `-Zcrate-attr`, which means we can't use
+# `rustc_strict_provenance_flags` below. Instead we filter out those lints to avoid unknown lint
+# warnings.
+#
+# See https://github.com/rust-lang/rust/issues/138491.
+rustc_strict_provenance_lints = -Wfuzzy_provenance_casts -Wlossy_provenance_casts
+
 quiet_cmd_rustdoc_test = RUSTDOC T $<
       cmd_rustdoc_test = \
 	RUST_MODFILE=test.rs \
 	OBJTREE=$(abspath $(objtree)) \
-	$(RUSTDOC) --test $(rust_common_flags) \
+	$(RUSTDOC) --test \
+		$(filter-out $(rustc_strict_provenance_lints),$(rust_common_flags)) \
 		@$(objtree)/include/generated/rustc_cfg \
 		$(rustc_target_flags) $(rustdoc_test_target_flags) \
 		$(rustdoc_test_quiet) \
@@ -171,7 +182,8 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 	rm -rf $(objtree)/$(obj)/test/doctests/kernel; \
 	mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
 	OBJTREE=$(abspath $(objtree)) \
-	$(RUSTDOC) --test $(rust_flags) \
+	$(RUSTDOC) --test \
+		$(filter-out $(rustc_strict_provenance_lints),$(rust_flags)) \
 		-L$(objtree)/$(obj) --extern ffi --extern kernel \
 		--extern build_error --extern macros \
 		--extern bindings --extern uapi \
@@ -193,6 +205,7 @@ quiet_cmd_rustc_test = $(RUSTC_OR_CLIPPY_QUIET) T  $<
       cmd_rustc_test = \
 	OBJTREE=$(abspath $(objtree)) \
 	$(RUSTC_OR_CLIPPY) --test $(rust_common_flags) \
+		$(rustc_strict_provenance_flags) \
 		@$(objtree)/include/generated/rustc_cfg \
 		$(rustc_target_flags) --out-dir $(objtree)/$(obj)/test \
 		-L$(objtree)/$(obj)/test \
@@ -362,6 +375,7 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
 quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
       cmd_rustc_procmacro = \
 	$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
+		$(rustc_strict_provenance_flags) \
 		-Clinker-flavor=gcc -Clinker=$(HOSTCC) \
 		-Clink-args='$(call escsq,$(KBUILD_PROCMACROLDFLAGS))' \
 		--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
@@ -376,7 +390,7 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L
       cmd_rustc_library = \
 	OBJTREE=$(abspath $(objtree)) \
 	$(if $(skip_clippy),$(RUSTC),$(RUSTC_OR_CLIPPY)) \
-		$(filter-out $(skip_flags),$(rust_flags) $(rustc_target_flags)) \
+		$(filter-out $(skip_flags),$(rust_flags) $(rustc_target_flags) $(rustc_strict_provenance_flags)) \
 		--emit=dep-info=$(depfile) --emit=obj=$@ \
 		--emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \
 		--crate-type rlib -L$(objtree)/$(obj) \
@@ -436,7 +450,7 @@ $(obj)/helpers/helpers.o: $(src)/helpers/helpers.c $(recordmcount_source) FORCE
 $(obj)/exports.o: private skip_gendwarfksyms = 1
 
 $(obj)/core.o: private skip_clippy = 1
-$(obj)/core.o: private skip_flags = -Wunreachable_pub
+$(obj)/core.o: private skip_flags = -Wunreachable_pub -Wlossy_provenance_casts $(rustc_strict_provenance_flags)
 $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
 $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
 $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs \

rust/kernel/alloc.rs

@@ -217,7 +217,7 @@ pub unsafe trait Allocator {
 
 /// Returns a properly aligned dangling pointer from the given `layout`.
 pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> {
-    let ptr = layout.align() as *mut u8;
+    let ptr = crate::with_exposed_provenance_mut(layout.align());
 
     // SAFETY: `layout.align()` (and hence `ptr`) is guaranteed to be non-zero.
     unsafe { NonNull::new_unchecked(ptr) }

rust/kernel/devres.rs

@@ -64,14 +64,14 @@ struct DevresInner<T> {
 ///             return Err(ENOMEM);
 ///         }
 ///
-///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
+///         Ok(IoMem(IoRaw::new(kernel::expose_provenance(addr), SIZE)?))
 ///     }
 /// }
 ///
 /// impl<const SIZE: usize> Drop for IoMem<SIZE> {
 ///     fn drop(&mut self) {
 ///         // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
-///         unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
+///         unsafe { bindings::iounmap(kernel::with_exposed_provenance_mut(self.0.addr())); };
 ///     }
 /// }
 ///

rust/kernel/io.rs

@@ -5,7 +5,7 @@
 //! C header: [`include/asm-generic/io.h`](srctree/include/asm-generic/io.h)
 
 use crate::error::{code::EINVAL, Result};
-use crate::{bindings, build_assert, ffi::c_void};
+use crate::{bindings, build_assert};
 
 /// Raw representation of an MMIO region.
 ///
@@ -75,14 +75,14 @@ impl<const SIZE: usize> IoRaw<SIZE> {
 ///             return Err(ENOMEM);
 ///         }
 ///
-///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
+///         Ok(IoMem(IoRaw::new(kernel::expose_provenance(addr), SIZE)?))
 ///     }
 /// }
 ///
 /// impl<const SIZE: usize> Drop for IoMem<SIZE> {
 ///     fn drop(&mut self) {
 ///         // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
-///         unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
+///         unsafe { bindings::iounmap(kernel::with_exposed_provenance_mut(self.0.addr())); };
 ///     }
 /// }
 ///
@@ -119,7 +119,7 @@ macro_rules! define_read {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            unsafe { bindings::$name(addr as *const c_void) }
+            unsafe { bindings::$name(crate::with_exposed_provenance(addr)) }
         }
 
         /// Read IO data from a given offset.
@@ -131,7 +131,7 @@ macro_rules! define_read {
             let addr = self.io_addr::<$type_name>(offset)?;
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            Ok(unsafe { bindings::$name(addr as *const c_void) })
+            Ok(unsafe { bindings::$name(crate::with_exposed_provenance(addr)) })
         }
     };
 }
@@ -148,7 +148,7 @@ macro_rules! define_write {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            unsafe { bindings::$name(value, addr as *mut c_void) }
+            unsafe { bindings::$name(value, crate::with_exposed_provenance_mut(addr)) }
         }
 
         /// Write IO data from a given offset.
@@ -160,7 +160,7 @@ macro_rules! define_write {
             let addr = self.io_addr::<$type_name>(offset)?;
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            unsafe { bindings::$name(value, addr as *mut c_void) }
+            unsafe { bindings::$name(value, crate::with_exposed_provenance_mut(addr)) }
             Ok(())
         }
     };

rust/kernel/lib.rs

@@ -25,6 +25,26 @@
 #![feature(const_ptr_write)]
 #![feature(const_refs_to_cell)]
 
+#[allow(clippy::incompatible_msrv)]
+mod strict_provenance {
+    #[doc(hidden)]
+    pub fn expose_provenance<T>(addr: *const T) -> usize {
+        addr.expose_provenance()
+    }
+
+    #[doc(hidden)]
+    pub fn with_exposed_provenance<T>(addr: usize) -> *const T {
+        core::ptr::with_exposed_provenance(addr)
+    }
+
+    #[doc(hidden)]
+    pub fn with_exposed_provenance_mut<T>(addr: usize) -> *mut T {
+        core::ptr::with_exposed_provenance_mut(addr)
+    }
+}
+
+pub use strict_provenance::*;
+
 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.
 #[cfg(not(CONFIG_RUST))]

rust/kernel/of.rs

@@ -22,7 +22,7 @@ unsafe impl RawDeviceId for DeviceId {
     const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::of_device_id, data);
 
     fn index(&self) -> usize {
-        self.0.data as usize
+        crate::expose_provenance(self.0.data)
     }
 }
 

rust/kernel/pci.rs

@@ -287,7 +287,7 @@ impl<const SIZE: usize> Bar<SIZE> {
         // `pdev` is valid by the invariants of `Device`.
         // `num` is checked for validity by a previous call to `Device::resource_len`.
         // `name` is always valid.
-        let ioptr: usize = unsafe { bindings::pci_iomap(pdev.as_raw(), num, 0) } as usize;
+        let ioptr = crate::expose_provenance(unsafe { bindings::pci_iomap(pdev.as_raw(), num, 0) });
         if ioptr == 0 {
             // SAFETY:
             // `pdev` valid by the invariants of `Device`.
@@ -320,7 +320,7 @@ impl<const SIZE: usize> Bar<SIZE> {
         // `ioptr` is valid by the safety requirements.
         // `num` is valid by the safety requirements.
         unsafe {
-            bindings::pci_iounmap(pdev.as_raw(), ioptr as *mut kernel::ffi::c_void);
+            bindings::pci_iounmap(pdev.as_raw(), crate::with_exposed_provenance_mut(ioptr));
             bindings::pci_release_region(pdev.as_raw(), num);
         }
     }

rust/kernel/str.rs

@@ -692,9 +692,9 @@ impl RawFormatter {
     pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
         // INVARIANT: The safety requirements guarantee the type invariants.
         Self {
-            beg: pos as usize,
-            pos: pos as usize,
-            end: end as usize,
+            beg: crate::expose_provenance(pos),
+            pos: crate::expose_provenance(pos),
+            end: crate::expose_provenance(end),
         }
     }
 
@@ -705,7 +705,7 @@ impl RawFormatter {
     /// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
     /// for the lifetime of the returned [`RawFormatter`].
     pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
-        let pos = buf as usize;
+        let pos = crate::expose_provenance(buf);
         // INVARIANT: We ensure that `end` is never less then `buf`, and the safety requirements
         // guarantees that the memory region is valid for writes.
         Self {
@@ -719,7 +719,7 @@ impl RawFormatter {
     ///
     /// N.B. It may point to invalid memory.
     pub(crate) fn pos(&self) -> *mut u8 {
-        self.pos as *mut u8
+        crate::with_exposed_provenance_mut(self.pos)
     }
 
     /// Returns the number of bytes written to the formatter.
@@ -741,11 +741,7 @@ impl fmt::Write for RawFormatter {
             // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
             // yet, so it is valid for write per the type invariants.
             unsafe {
-                core::ptr::copy_nonoverlapping(
-                    s.as_bytes().as_ptr(),
-                    self.pos as *mut u8,
-                    len_to_copy,
-                )
+                core::ptr::copy_nonoverlapping(s.as_bytes().as_ptr(), self.pos(), len_to_copy)
             };
         }
 

rust/kernel/uaccess.rs

@@ -226,7 +226,9 @@ impl UserSliceReader {
         }
         // SAFETY: `out_ptr` points into a mutable slice of length `len`, so we may write
         // that many bytes to it.
-        let res = unsafe { bindings::copy_from_user(out_ptr, self.ptr as *const c_void, len) };
+        let res = unsafe {
+            bindings::copy_from_user(out_ptr, crate::with_exposed_provenance(self.ptr), len)
+        };
         if res != 0 {
             return Err(EFAULT);
         }
@@ -264,7 +266,7 @@ impl UserSliceReader {
         let res = unsafe {
             bindings::_copy_from_user(
                 out.as_mut_ptr().cast::<c_void>(),
-                self.ptr as *const c_void,
+                crate::with_exposed_provenance(self.ptr),
                 len,
             )
         };
@@ -330,7 +332,9 @@ impl UserSliceWriter {
         }
         // SAFETY: `data_ptr` points into an immutable slice of length `len`, so we may read
         // that many bytes from it.
-        let res = unsafe { bindings::copy_to_user(self.ptr as *mut c_void, data_ptr, len) };
+        let res = unsafe {
+            bindings::copy_to_user(crate::with_exposed_provenance_mut(self.ptr), data_ptr, len)
+        };
         if res != 0 {
             return Err(EFAULT);
         }
@@ -357,7 +361,7 @@ impl UserSliceWriter {
         // is a compile-time constant.
         let res = unsafe {
             bindings::_copy_to_user(
-                self.ptr as *mut c_void,
+                crate::with_exposed_provenance_mut(self.ptr),
                 (value as *const T).cast::<c_void>(),
                 len,
             )

scripts/Makefile.build

@@ -226,7 +226,7 @@ $(obj)/%.lst: $(obj)/%.c FORCE
 # Compile Rust sources (.rs)
 # ---------------------------------------------------------------------------
 
-rust_allowed_features := asm_const,asm_goto,arbitrary_self_types,lint_reasons
+rust_allowed_features := asm_const,asm_goto,arbitrary_self_types,lint_reasons,$(rustc_strict_provenance_feature)
 
 # `--out-dir` is required to avoid temporaries being created by `rustc` in the
 # current working directory, which may be not accessible in the out-of-tree

scripts/Makefile.host

@@ -87,10 +87,14 @@ hostcxx_flags  = -Wp,-MMD,$(depfile) \
                  $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(target-stem).o)
 
+rust_allowed_features := $(rustc_strict_provenance_feature)
+
 # `--out-dir` is required to avoid temporaries being created by `rustc` in the
 # current working directory, which may be not accessible in the out-of-tree
 # modules case.
 hostrust_flags = --out-dir $(dir $@) --emit=dep-info=$(depfile) \
+		 -Zallow-features=$(rust_allowed_features) \
+		 -Zcrate-attr='feature($(rust_allowed_features))' \
 		 -Clinker-flavor=gcc -Clinker=$(HOSTCC) \
 		 -Clink-args='$(call escsq,$(KBUILD_HOSTLDFLAGS))' \
                  $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \