Re: [PATCH v5 6/6] rust: use strict provenance APIs

Boqun Feng
2025-03-18T00:11:44Z

On Mon, Mar 17, 2025 at 02:36:08PM -0700, Boqun Feng wrote:
[...]
> >
> > What about `pointer::expose_provenance`? It's a method that was added in 1.79.0.
> >
>
> We have a few options:
>
> 1) we can decide to use funtion-version of expose_provenance() (i.e. the
> stub), if we feel the symmetry with with_exposed_provenance() is
> a strong rationale. This also means we won't likely use
> pointer::expose_provenance() in the future. That is, although kernel
> doesn't have stable internal API, but in the foreseeable future, we
> decide to use funtion-version of expose_provenance().
>
> 2) we can introduce a PtrExt trait for <1.79
>
> pub trait PtrExt<T> {
> fn expose_provenance(self) -> usize;
> }
>
> and
>
> impl<T> PtrExt<T> for *const T {
> ...
> }
>
> and `PtrExt` in kernel::prelude.
>
> (we need to #[allow(unstable_name_collisions)] to make that work)
>
> We can also make with_exposed_provenance() use the same *Ext trick,
> and remove it when we bump the minimal rustc version.

This is probably a wrong suggestion, because with_exposed_provenance()
is a function instead of a method in Rust std.

Below is what I combined all together (based on your v5 patchset), and I
did test on 1.78, 1.79, 1.84 and 1.85 and it seems working ;-)

Regards,
Boqun
------------------------------------->8
diff --git a/init/Kconfig b/init/Kconfig
index 82e28d6f7c3f..e316b98b3612 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -135,6 +135,9 @@ config RUSTC_HAS_COERCE_POINTEE
config RUSTC_HAS_STABLE_STRICT_PROVENANCE
def_bool RUSTC_VERSION >= 108400

+config RUSTC_HAS_EXPOSED_PROVENANCE
+ def_bool RUSTC_VERSION >= 107900
+
config PAHOLE_VERSION
int
default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index e8232bb771b2..a87a437bd9ab 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -64,7 +64,7 @@ struct DevresInner<T> {
/// return Err(ENOMEM);
/// }
///
-/// Ok(IoMem(IoRaw::new(kernel::expose_provenance(addr), SIZE)?))
+/// Ok(IoMem(IoRaw::new(addr.expose_provenance(), SIZE)?))
/// }
/// }
///
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index 0a018ad7478a..60c71f26d29d 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -75,7 +75,7 @@ pub fn maxsize(&self) -> usize {
/// return Err(ENOMEM);
/// }
///
-/// Ok(IoMem(IoRaw::new(kernel::expose_provenance(addr), SIZE)?))
+/// Ok(IoMem(IoRaw::new(addr.expose_provenance(), SIZE)?))
/// }
/// }
///
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index c1b274c04a0f..79b19e601372 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -22,6 +22,9 @@
feature(strict_provenance_lints),
deny(fuzzy_provenance_casts, lossy_provenance_casts)
)]
+#![cfg_attr(not(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE), feature(strict_provenance))]
+#![cfg_attr(all(not(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE), CONFIG_RUSTC_HAS_EXPOSED_PROVENANCE), feature(exposed_provenance))]
+
#![feature(inline_const)]
#![feature(lint_reasons)]
// Stable in Rust 1.83
@@ -30,78 +33,24 @@
#![feature(const_ptr_write)]
#![feature(const_refs_to_cell)]

-#[cfg(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE)]
-#[allow(clippy::incompatible_msrv)]
-mod strict_provenance {
- /// Gets the "address" portion of the pointer.
- ///
- /// See https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.addr.
- #[inline]
- pub fn addr<T>(ptr: *const T) -> usize {
- ptr.addr()
- }
-
- /// Exposes the "provenance" part of the pointer for future use in
- /// [`with_exposed_provenance`] and returns the "address" portion.
- ///
- /// See https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.expose_provenance.
- #[inline]
- pub fn expose_provenance<T>(ptr: *const T) -> usize {
- ptr.expose_provenance()
- }
-
- /// Converts an address back to a pointer, picking up some previously 'exposed'
- /// provenance.
- ///
- /// See https://doc.rust-lang.org/stable/core/ptr/fn.with_exposed_provenance.html.
- #[inline]
- pub fn with_exposed_provenance<T>(addr: usize) -> *const T {
- core::ptr::with_exposed_provenance(addr)
- }
-
- /// Converts an address back to a mutable pointer, picking up some previously 'exposed'
- /// provenance.
- ///
- /// See https://doc.rust-lang.org/stable/core/ptr/fn.with_exposed_provenance_mut.html
- #[inline]
- pub fn with_exposed_provenance_mut<T>(addr: usize) -> *mut T {
- core::ptr::with_exposed_provenance_mut(addr)
- }
-
- /// Creates a pointer with the given address and no [provenance][crate::ptr#provenance].
- ///
- /// See https://doc.rust-lang.org/stable/core/ptr/fn.without_provenance_mut.html.
- #[inline]
- pub fn without_provenance_mut<T>(addr: usize) -> *mut T {
- core::ptr::without_provenance_mut(addr)
- }
-}
+#![allow(clippy::incompatible_msrv)]

-#[cfg(not(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE))]
+#[cfg(not(CONFIG_RUSTC_HAS_EXPOSED_PROVENANCE))]
mod strict_provenance {
- /// Gets the "address" portion of the pointer.
- ///
- /// See https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.addr.
- #[inline]
- pub fn addr<T>(ptr: *const T) -> usize {
- // This is core's implementation from
- // https://github.com/rust-lang/rust/commit/4291332175d12e79e6061cdc3f5dccac2e28b969 through
- // https://github.com/rust-lang/rust/blob/1.84.0/library/core/src/ptr/const_ptr.rs#L172
- // which is the first version that satisfies `CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE`.
- #[allow(clippy::undocumented_unsafe_blocks)]
- unsafe {
- #[allow(clippy::transmutes_expressible_as_ptr_casts)]
- core::mem::transmute(ptr.cast::<()>())
- }
+ #[doc(hidden)]
+ pub trait PtrExt<T> {
+ /// Exposes the "provenance" part of the pointer for future use in
+ /// [`with_exposed_provenance`] and returns the "address" portion.
+ ///
+ /// See https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.expose_provenance.
+ fn expose_provenance(self) -> usize;
}

- /// Exposes the "provenance" part of the pointer for future use in
- /// [`with_exposed_provenance`] and returns the "address" portion.
- ///
- /// See https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.expose_provenance.
- #[inline]
- pub fn expose_provenance<T>(ptr: *const T) -> usize {
- ptr.cast::<()>() as usize
+ impl<T> PtrExt<T> for *const T {
+ #[inline]
+ fn expose_provenance(self) -> usize {
+ self.cast::<()>() as usize
+ }
}

/// Converts an address back to a pointer, picking up some previously 'exposed'
@@ -131,8 +80,12 @@ pub fn without_provenance_mut<T>(addr: usize) -> *mut T {
}
}

+#[cfg(not(CONFIG_RUSTC_HAS_EXPOSED_PROVENANCE))]
pub use strict_provenance::*;

+#[cfg(CONFIG_RUSTC_HAS_EXPOSED_PROVENANCE)]
+pub use core::ptr::{with_exposed_provenance, with_exposed_provenance_mut, without_provenance_mut};
+
// Ensure conditional compilation based on the kernel configuration works;
// otherwise we may silently break things like initcall handling.
#[cfg(not(CONFIG_RUST))]
diff --git a/rust/kernel/of.rs b/rust/kernel/of.rs
index b70076d16008..3670676071ff 100644
--- a/rust/kernel/of.rs
+++ b/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 {
- crate::addr(self.0.data)
+ self.0.data.addr()
}
}

diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index 87c9f67b3f0f..73958abdc522 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -287,7 +287,7 @@ fn new(pdev: Device, num: u32, name: &CStr) -> Result<Self> {
// `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 = crate::expose_provenance(unsafe { bindings::pci_iomap(pdev.as_raw(), num, 0) });
+ let ioptr = unsafe { bindings::pci_iomap(pdev.as_raw(), num, 0) }.expose_provenance();
if ioptr == 0 {
// SAFETY:
// `pdev` valid by the invariants of `Device`.
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index baa774a351ce..3ea6aa9e40e5 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -41,3 +41,6 @@
pub use super::init::InPlaceInit;

pub use super::current;
+
+#[cfg(not(CONFIG_RUSTC_HAS_EXPOSED_PROVENANCE))]
+pub use super::PtrExt;
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 6bc6357293e4..d8e740267f14 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -8,6 +8,9 @@

use crate::error::{code::*, Error};

+#[cfg(not(CONFIG_RUSTC_HAS_EXPOSED_PROVENANCE))]
+use crate::PtrExt;
+
/// Byte string without UTF-8 validity guarantee.
#[repr(transparent)]
pub struct BStr([u8]);
@@ -692,9 +695,9 @@ fn new() -> Self {
pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
// INVARIANT: The safety requirements guarantee the type invariants.
Self {
- beg: crate::expose_provenance(pos),
- pos: crate::expose_provenance(pos),
- end: crate::expose_provenance(end),
+ beg: pos.expose_provenance(),
+ pos: pos.expose_provenance(),
+ end: end.expose_provenance(),
}
}

@@ -705,7 +708,7 @@ pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
/// 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 = crate::expose_provenance(buf);
+ let pos = buf.expose_provenance();
// INVARIANT: We ensure that `end` is never less then `buf`, and the safety requirements
// guarantees that the memory region is valid for writes.
Self {
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 08b6380933f5..b070da0ea972 100644
--- a/scripts/Makefile.build
+++ b/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,exposed_provenance

# `--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
diff --git a/scripts/rustdoc_test_gen.rs b/scripts/rustdoc_test_gen.rs
index 036635fb1621..331ed32adc35 100644
--- a/scripts/rustdoc_test_gen.rs
+++ b/scripts/rustdoc_test_gen.rs
@@ -224,6 +224,8 @@ macro_rules! assert_eq {{
BufWriter::new(File::create("rust/doctests_kernel_generated.rs").unwrap()),
r#"//! `kernel` crate documentation tests.

+#![allow(clippy::incompatible_msrv)]
+
const __LOG_PREFIX: &[u8] = b"rust_doctests_kernel\0";

{rust_tests}