[PATCH v5 0/4] rust: Add safe pointer formatting support

[PATCH v5 0/4] rust: Add safe pointer formatting support

[Ke Sun]

This patch series adds safe pointer formatting support for Rust kernel code,
providing three pointer wrapper types (HashedPtr, RawPtr, RestrictedPtr) that
correspond to C kernel's printk format specifiers %p, %px, and %pK.

The implementation ensures that raw pointers are automatically hashed when
formatted with {:p}, providing safe default behavior that prevents information
leaks about kernel memory layout. Users can also explicitly use wrapper types
when they need specific formatting behavior.

---
v5:
- Format use statements in rust/kernel/ptr.rs and rust/kernel/fmt.rs using kernel
  vertical style with alphabetical ordering
- Remove unnecessary SAFETY comment in rust/kernel/ptr.rs (addressed Clippy warning)
- Update type ordering to alphabetical (HashedPtr, RawPtr, RestrictedPtr) in
  fmt.rs macro invocation

v4: https://lore.kernel.org/rust-for-linux/20251225225709.3944255-1-sunke@kylinos.cn/
- Use Pointer::fmt() instead of write!(f, "{:p}", ...) to preserve formatting
  options (width, alignment, padding characters)
- Improve code structure: reduce unsafe block scope, use early return pattern
- Add doctests with formatting option tests for all pointer wrapper types
- Enhance documentation with detailed formatting options section, including
  examples for width, alignment, and padding
- Fix RestrictedPtr example to use pr_info! instead of seq_print! in docs

v3: https://lore.kernel.org/rust-for-linux/20251224081315.729684-1-sunke@kylinos.cn/
- Export ptr_to_hashval() from lib/vsprintf.c for Rust pointer hashing
- Add three pointer wrapper types (HashedPtr, RestrictedPtr, RawPtr) in
  rust/kernel/ptr.rs corresponding to %p, %pK, and %px
- Make raw pointers automatically use HashedPtr when formatted with {:p}
- Add documentation for pointer wrapper types

v2: https://lore.kernel.org/rust-for-linux/20251223033018.2814732-1-sunke@kylinos.cn/
- Disabled {:p} raw pointer printing by default to prevent accidental
  information leaks

v1: https://lore.kernel.org/rust-for-linux/20251218032709.2184890-1-sunke@kylinos.cn/
- Initial implementation that directly printed raw pointers
---

Ke Sun (4):
  lib/vsprintf: Export ptr_to_hashval for Rust use
  rust: kernel: Add pointer wrapper types for safe pointer formatting
  rust: fmt: Default raw pointer formatting to HashedPtr
  docs: rust: Add pointer formatting documentation

 Documentation/rust/index.rst              |   1 +
 Documentation/rust/pointer-formatting.rst | 101 +++++++++
 lib/vsprintf.c                            |   1 +
 rust/helpers/fmt.c                        |  65 ++++++
 rust/helpers/helpers.c                    |   3 +-
 rust/kernel/fmt.rs                        |  69 ++++++-
 rust/kernel/ptr.rs                        | 240 +++++++++++++++++++++-
 7 files changed, 475 insertions(+), 5 deletions(-)
 create mode 100644 Documentation/rust/pointer-formatting.rst
 create mode 100644 rust/helpers/fmt.c

-- 
2.43.0

[PATCH v5 1/4] lib/vsprintf: Export ptr_to_hashval for Rust use

[Ke Sun]

Export ptr_to_hashval() with EXPORT_SYMBOL_GPL to allow Rust code
to call this function for pointer hashing, which is needed for the
HashedPtr and RestrictedPtr wrapper types in rust/kernel/ptr.rs.

This function is used to hash kernel pointers before printing them,
preventing information leaks about kernel memory layout.

Signed-off-by: Ke Sun <sunke@kylinos.cn>
---
 lib/vsprintf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index a3790c43a0aba..d1c682afd792c 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -811,6 +811,7 @@ int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
 {
 	return __ptr_to_hashval(ptr, hashval_out);
 }
+EXPORT_SYMBOL_GPL(ptr_to_hashval);
 
 static char *ptr_to_id(char *buf, char *end, const void *ptr,
 		       struct printf_spec spec)
-- 
2.43.0

[PATCH v5 2/4] rust: kernel: Add pointer wrapper types for safe pointer formatting

[Ke Sun]

Add three pointer wrapper types (HashedPtr, RestrictedPtr, RawPtr) to
rust/kernel/ptr.rs that correspond to C kernel's printk format specifiers
%p, %pK, and %px. These types provide type-safe pointer formatting that
matches C kernel patterns.

These wrapper types implement core::fmt::Pointer and delegate to the
corresponding kernel formatting functions, enabling safe pointer
formatting in Rust code that prevents information leaks about kernel
memory layout.

Users can explicitly use these types:
    pr_info!("{:p}\n", HashedPtr::from(ptr));
    pr_info!("{:p}\n", RestrictedPtr::from(ptr));
    pr_info!("{:p}\n", RawPtr::from(ptr));

Signed-off-by: Ke Sun <sunke@kylinos.cn>
---
 rust/helpers/fmt.c     |  65 +++++++++++
 rust/helpers/helpers.c |   3 +-
 rust/kernel/ptr.rs     | 240 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 304 insertions(+), 4 deletions(-)
 create mode 100644 rust/helpers/fmt.c

diff --git a/rust/helpers/fmt.c b/rust/helpers/fmt.c
new file mode 100644
index 0000000000000..4ee716bbfe284
--- /dev/null
+++ b/rust/helpers/fmt.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2018 - 2025 KylinSoft Co., Ltd. All rights reserved.
+ * Copyright (C) 2018 - 2025 Ke Sun <sunke@kylinos.cn>
+ */
+
+#include <linux/kernel.h>
+#include <linux/cred.h>
+#include <linux/capability.h>
+#include <linux/hardirq.h>
+#include <linux/printk.h>
+
+/*
+ * Helper function for Rust to format a restricted pointer (%pK).
+ *
+ * This function determines what pointer value should be printed based on the
+ * kptr_restrict sysctl setting:
+ *
+ * - kptr_restrict == 0: Returns the original pointer (will be hashed by caller)
+ * - kptr_restrict == 1: Returns the original pointer if the current process has
+ *                       CAP_SYSLOG and same euid/egid, NULL otherwise
+ * - kptr_restrict >= 2: Always returns NULL
+ *
+ * Returns:
+ *   - The original pointer if it should be printed (case 0 or case 1 with permission)
+ *   - NULL if it should not be printed (no permission, IRQ context, or restrict >= 2)
+ */
+const void *rust_helper_kptr_restrict_value(const void *ptr)
+{
+	switch (kptr_restrict) {
+	case 0:
+		/* Handle as %p - return original pointer for hashing */
+		return ptr;
+	case 1: {
+		const struct cred *cred;
+
+		/*
+		 * kptr_restrict==1 cannot be used in IRQ context because the
+		 * capability check would be meaningless (no process context).
+		 */
+		if (in_hardirq() || in_serving_softirq() || in_nmi())
+			return NULL;
+
+		/*
+		 * Only return the real pointer value if the current process has
+		 * CAP_SYSLOG and is running with the same credentials it started with.
+		 * This prevents privilege escalation attacks where a process opens a
+		 * file with %pK, then elevates privileges before reading it.
+		 */
+		cred = current_cred();
+		if (!has_capability_noaudit(current, CAP_SYSLOG) ||
+		    !uid_eq(cred->euid, cred->uid) ||
+		    !gid_eq(cred->egid, cred->gid))
+			return NULL;
+		break;
+	}
+	case 2:
+	default:
+		/* Always hide pointer values when kptr_restrict >= 2 */
+		return NULL;
+	}
+
+	return ptr;
+}
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 79c72762ad9c4..b6877fe8dafc0 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -27,8 +27,9 @@
 #include "dma.c"
 #include "drm.c"
 #include "err.c"
-#include "irq.c"
+#include "fmt.c"
 #include "fs.c"
+#include "irq.c"
 #include "io.c"
 #include "jump_label.c"
 #include "kunit.c"
diff --git a/rust/kernel/ptr.rs b/rust/kernel/ptr.rs
index e3893ed04049d..ed5069c954146 100644
--- a/rust/kernel/ptr.rs
+++ b/rust/kernel/ptr.rs
@@ -1,11 +1,22 @@
 // SPDX-License-Identifier: GPL-2.0
 
 //! Types and functions to work with pointers and addresses.
+//!
+//! This module provides wrapper types for formatting kernel pointers that correspond to the
+//! C kernel's printk format specifiers `%p`, `%pK`, and `%px`.
 
-use core::mem::align_of;
-use core::num::NonZero;
+use core::{
+    fmt,
+    fmt::Pointer,
+    mem::align_of,
+    num::NonZero, //
+};
 
-use crate::build_assert;
+use crate::{
+    bindings,
+    build_assert,
+    ffi::c_void, //
+};
 
 /// Type representing an alignment, which is always a power of two.
 ///
@@ -225,3 +236,226 @@ fn align_up(self, alignment: Alignment) -> Option<Self> {
 }
 
 impl_alignable_uint!(u8, u16, u32, u64, usize);
+
+/// Placeholder string used when pointer hashing is not ready yet.
+const PTR_PLACEHOLDER: &str = if core::mem::size_of::<*const c_void>() == 8 {
+    "(____ptrval____)"
+} else {
+    "(ptrval)"
+};
+
+/// Macro to implement common methods for pointer wrapper types.
+macro_rules! impl_ptr_wrapper {
+    ($($name:ident),* $(,)?) => {
+        $(
+            impl $name {
+                /// Creates a new instance from a raw pointer.
+                #[inline]
+                pub fn from<T>(ptr: *const T) -> Self {
+                    Self(ptr.cast())
+                }
+
+                /// Creates a new instance from a mutable raw pointer.
+                #[inline]
+                pub fn from_mut<T>(ptr: *mut T) -> Self {
+                    Self(ptr.cast())
+                }
+
+                /// Returns the inner raw pointer.
+                #[inline]
+                pub fn as_ptr(&self) -> *const c_void {
+                    self.0
+                }
+            }
+
+            impl<T> From<*const T> for $name {
+                #[inline]
+                fn from(ptr: *const T) -> Self {
+                    Self::from(ptr)
+                }
+            }
+
+            impl<T> From<*mut T> for $name {
+                #[inline]
+                fn from(ptr: *mut T) -> Self {
+                    Self::from_mut(ptr)
+                }
+            }
+        )*
+    };
+}
+
+/// Helper function to hash a pointer and format it.
+///
+/// Returns `Ok(())` if the hash was successfully computed and formatted,
+/// or the placeholder string if hashing is not ready yet.
+fn format_hashed_ptr(ptr: *const c_void, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    let mut hashval: crate::ffi::c_ulong = 0;
+    // SAFETY: We're calling the kernel's ptr_to_hashval function which handles
+    // hashing. This is safe as long as ptr is a valid pointer value.
+    let ret = unsafe { bindings::ptr_to_hashval(ptr, core::ptr::addr_of_mut!(hashval)) };
+
+    if ret != 0 {
+        // Hash not ready yet, print placeholder
+        return f.write_str(PTR_PLACEHOLDER);
+    }
+
+    // Successfully got hash value, format it using Pointer::fmt to preserve
+    // formatting options (width, alignment, padding, etc.)
+    Pointer::fmt(&(hashval as *const c_void), f)
+}
+
+/// A pointer that will be hashed when printed (corresponds to `%p`).
+///
+/// This is the default behavior for kernel pointers - they are hashed to prevent
+/// leaking information about the kernel memory layout.
+///
+/// # Example
+///
+/// ```
+/// use kernel::{
+///     prelude::fmt,
+///     ptr::HashedPtr,
+///     str::CString, //
+/// };
+///
+/// let ptr = HashedPtr::from(0x12345678 as *const u8);
+/// pr_info!("Hashed pointer: {:016p}\n", ptr);
+///
+/// // Width option test
+/// let cstr = CString::try_from_fmt(fmt!("{:30p}", ptr))?;
+/// let width_30 = cstr.to_str()?;
+/// assert_eq!(width_30.len(), 30);
+/// # Ok::<(), kernel::error::Error>(())
+/// ```
+#[repr(transparent)]
+#[derive(Copy, Clone, Debug)]
+pub struct HashedPtr(*const c_void);
+
+impl fmt::Pointer for HashedPtr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Handle NULL pointers - print them directly
+        if self.0.is_null() {
+            return Pointer::fmt(&self.0, f);
+        }
+
+        format_hashed_ptr(self.0, f)
+    }
+}
+
+/// A pointer that will be restricted based on `kptr_restrict` when printed (corresponds to `%pK`).
+///
+/// This is intended for use in procfs/sysfs files that are read by userspace.
+/// The behavior depends on the `kptr_restrict` sysctl setting.
+///
+/// # Example
+///
+/// ```
+/// use kernel::{
+///     prelude::fmt,
+///     ptr::RestrictedPtr,
+///     str::CString, //
+/// };
+///
+/// let ptr = RestrictedPtr::from(0x12345678 as *const u8);
+/// pr_info!("Restricted pointer: {:016p}\n", ptr);
+///
+/// // Width option test
+/// let cstr = CString::try_from_fmt(fmt!("{:30p}", ptr))?;
+/// let width_30 = cstr.to_str()?;
+/// assert_eq!(width_30.len(), 30);
+/// # Ok::<(), kernel::error::Error>(())
+/// ```
+#[repr(transparent)]
+#[derive(Copy, Clone, Debug)]
+pub struct RestrictedPtr(*const c_void);
+
+impl fmt::Pointer for RestrictedPtr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Handle NULL pointers
+        if self.0.is_null() {
+            return Pointer::fmt(&self.0, f);
+        }
+
+        // Use kptr_restrict_value to handle all kptr_restrict cases.
+        // SAFETY: kptr_restrict_value handles capability checks and IRQ context.
+        // - Returns NULL if no permission, IRQ context, or kptr_restrict >= 2
+        // - Returns the original pointer if kptr_restrict == 0 (needs hashing)
+        // - Returns the original pointer if kptr_restrict == 1 with permission (print raw)
+        let restricted_ptr = unsafe { bindings::kptr_restrict_value(self.0) };
+
+        if restricted_ptr.is_null() {
+            // No permission, IRQ context, or kptr_restrict >= 2 - print 0
+            return Pointer::fmt(&core::ptr::null::<c_void>(), f);
+        }
+
+        // restricted_ptr is non-null, meaning we should print something.
+        // SAFETY: Reading kptr_restrict is safe as it's a kernel variable.
+        let restrict = unsafe { bindings::kptr_restrict };
+
+        if restrict == 0 {
+            // kptr_restrict == 0: hash the pointer (same as %p)
+            format_hashed_ptr(self.0, f)
+        } else {
+            // kptr_restrict == 1 with permission: print the raw pointer directly (like %px)
+            // This matches C behavior: pointer_string() prints the raw address
+            Pointer::fmt(&restricted_ptr, f)
+        }
+    }
+}
+
+/// A pointer that will be printed as its raw address (corresponds to `%px`).
+///
+/// **Warning**: This exposes the real kernel address and should only be used
+/// for debugging purposes. Consider using [`HashedPtr`] or [`RestrictedPtr`] instead.
+///
+/// # Example
+///
+/// ```
+/// use kernel::{
+///     prelude::fmt,
+///     ptr::RawPtr,
+///     str::CString, //
+/// };
+///
+/// let ptr = RawPtr::from(0x12345678 as *const u8);
+///
+/// // Basic formatting
+/// let cstr = CString::try_from_fmt(fmt!("{:p}", ptr))?;
+/// let formatted = cstr.to_str()?;
+/// assert_eq!(formatted, "0x12345678");
+///
+/// // Right align with zero padding, width 30
+/// let cstr = CString::try_from_fmt(fmt!("{:0>30p}", ptr))?;
+/// let right_zero = cstr.to_str()?;
+/// assert_eq!(right_zero, "000000000000000000000x12345678");
+///
+/// // Left align with zero padding, width 30
+/// let cstr = CString::try_from_fmt(fmt!("{:0<30p}", ptr))?;
+/// let left_zero = cstr.to_str()?;
+/// assert_eq!(left_zero, "0x1234567800000000000000000000");
+///
+/// // Center align with zero padding, width 30
+/// let cstr = CString::try_from_fmt(fmt!("{:0^30p}", ptr))?;
+/// let center_zero = cstr.to_str()?;
+/// assert_eq!(center_zero, "00000000000x123456780000000000");
+/// # Ok::<(), kernel::error::Error>(())
+/// ```
+#[repr(transparent)]
+#[derive(Copy, Clone, Debug)]
+pub struct RawPtr(*const c_void);
+
+impl fmt::Pointer for RawPtr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Directly format the raw address - no hashing or restriction.
+        // This corresponds to %px behavior.
+        Pointer::fmt(&self.0, f)
+    }
+}
+
+// Implement common methods for all pointer wrapper types
+impl_ptr_wrapper!(
+    HashedPtr,
+    RawPtr,
+    RestrictedPtr, //
+);
-- 
2.43.0

[PATCH v5 3/4] rust: fmt: Default raw pointer formatting to HashedPtr

[Ke Sun]

Make raw pointers (*const T, *mut T) automatically use HashedPtr when
formatted with {:p}, providing safe default behavior for kernel pointers.

This allows users to format raw pointers directly:
    pr_info!("{:p}\n", ptr);  // Automatically hashed

While still allowing explicit use of wrapper types when needed:
    pr_info!("{:p}\n", RestrictedPtr::from(ptr));
    pr_info!("{:p}\n", RawPtr::from(ptr));

Signed-off-by: Ke Sun <sunke@kylinos.cn>
---
 rust/kernel/fmt.rs | 69 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 68 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/fmt.rs b/rust/kernel/fmt.rs
index 84d634201d90a..197687261b4e9 100644
--- a/rust/kernel/fmt.rs
+++ b/rust/kernel/fmt.rs
@@ -6,6 +6,12 @@
 
 pub use core::fmt::{Arguments, Debug, Error, Formatter, Result, Write};
 
+use crate::ptr::{
+    HashedPtr,
+    RawPtr,
+    RestrictedPtr, //
+};
+
 /// Internal adapter used to route allow implementations of formatting traits for foreign types.
 ///
 /// It is inserted automatically by the [`fmt!`] macro and is not meant to be used directly.
@@ -28,7 +34,68 @@ fn fmt(&self, f: &mut Formatter<'_>) -> Result {
 }
 
 use core::fmt::{Binary, LowerExp, LowerHex, Octal, Pointer, UpperExp, UpperHex};
-impl_fmt_adapter_forward!(Debug, LowerHex, UpperHex, Octal, Binary, Pointer, LowerExp, UpperExp);
+impl_fmt_adapter_forward!(Debug, LowerHex, UpperHex, Octal, Binary, LowerExp, UpperExp);
+
+// Special handling for Pointer: default to HashedPtr for raw pointers.
+// This overrides the default Pointer implementation for raw pointers to use hashing,
+// which is the safe default behavior for kernel pointers.
+impl<T> Pointer for Adapter<*const T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        let Self(ptr) = self;
+        Pointer::fmt(&HashedPtr::from(*ptr), f)
+    }
+}
+
+impl<T> Pointer for Adapter<*mut T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        let Self(ptr) = self;
+        Pointer::fmt(&HashedPtr::from_mut(*ptr), f)
+    }
+}
+
+// Handle references to raw pointers (needed when pointers are passed by reference in macros).
+impl<T> Pointer for Adapter<&*const T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        let Self(ptr) = self;
+        Pointer::fmt(&HashedPtr::from(**ptr), f)
+    }
+}
+
+impl<T> Pointer for Adapter<&*mut T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        let Self(ptr) = self;
+        Pointer::fmt(&HashedPtr::from_mut(**ptr), f)
+    }
+}
+
+// For wrapper types that implement Pointer (like HashedPtr, RawPtr, RestrictedPtr),
+// forward to their implementation. This allows explicit wrapper types to use their
+// own formatting logic instead of being converted to HashedPtr.
+macro_rules! impl_pointer_adapter_forward {
+    ($($ty:ty),* $(,)?) => {
+        $(
+            impl Pointer for Adapter<$ty> {
+                fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                    let Self(t) = self;
+                    Pointer::fmt(t, f)
+                }
+            }
+
+            impl Pointer for Adapter<&$ty> {
+                fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                    let Self(t) = self;
+                    Pointer::fmt(*t, f)
+                }
+            }
+        )*
+    };
+}
+
+impl_pointer_adapter_forward!(
+    HashedPtr,
+    RawPtr,
+    RestrictedPtr, //
+);
 
 /// A copy of [`core::fmt::Display`] that allows us to implement it for foreign types.
 ///
-- 
2.43.0

[PATCH v5 4/4] docs: rust: Add pointer formatting documentation

[Ke Sun]

Add a brief documentation for Rust pointer wrapper types (HashedPtr,
RestrictedPtr, RawPtr) that correspond to C kernel's printk format
specifiers %p, %pK, and %px.

The documentation provides:
- Overview of the three wrapper types
- Usage examples for each type
- When to use each type
- Security considerations

This complements the general pointer formatting documentation in
Documentation/core-api/printk-formats.rst.

Signed-off-by: Ke Sun <sunke@kylinos.cn>
---
 Documentation/rust/index.rst              |   1 +
 Documentation/rust/pointer-formatting.rst | 101 ++++++++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 Documentation/rust/pointer-formatting.rst

diff --git a/Documentation/rust/index.rst b/Documentation/rust/index.rst
index ec62001c7d8c7..4f4f8b393031e 100644
--- a/Documentation/rust/index.rst
+++ b/Documentation/rust/index.rst
@@ -55,6 +55,7 @@ more details.
     coding-guidelines
     arch-support
     testing
+    pointer-formatting
 
 You can also find learning materials for Rust in its section in
 :doc:`../process/kernel-docs`.
diff --git a/Documentation/rust/pointer-formatting.rst b/Documentation/rust/pointer-formatting.rst
new file mode 100644
index 0000000000000..9407307216c9a
--- /dev/null
+++ b/Documentation/rust/pointer-formatting.rst
@@ -0,0 +1,101 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Pointer Formatting in Rust
+===========================
+
+This document describes how to format kernel pointers safely in Rust code,
+corresponding to the C kernel's printk format specifiers ``%p``, ``%pK``, and ``%px``.
+
+For general information about pointer formatting in the kernel, please refer to
+:doc:`../core-api/printk-formats`.
+
+Overview
+--------
+
+The Rust kernel provides three wrapper types for formatting kernel pointers:
+
+- **``HashedPtr``** → ``%p`` (hashed, default)
+- **``RestrictedPtr``** → ``%pK`` (restricted, respects ``kptr_restrict``)
+- **``RawPtr``** → ``%px`` (raw address, debug only)
+
+When formatting raw pointers (``*const T`` or ``*mut T``) with ``{:p}``,
+they are automatically wrapped with ``HashedPtr``, providing safe default behavior.
+
+HashedPtr (%p)
+--------------
+
+Use ``HashedPtr`` for general kernel logging. Pointers are hashed before printing
+to prevent leaking information about the kernel memory layout.
+
+**Example**::
+
+    use kernel::ptr::HashedPtr;
+
+    pr_info!("Device pointer: {:p}\n", HashedPtr::from(ptr));
+
+RestrictedPtr (%pK)
+-------------------
+
+Use ``RestrictedPtr`` when producing content of a file read by userspace from
+e.g. procfs or sysfs (using e.g. ``seq_print!()``, not ``pr_info!()``). The behavior
+depends on the ``kptr_restrict`` sysctl setting.
+
+**Example**::
+
+    use kernel::ptr::RestrictedPtr;
+
+    seq_print!(seq_file, "Pointer: {:p}\n", RestrictedPtr::from(ptr));
+
+For more details about ``kptr_restrict``, see :doc:`../admin-guide/sysctl/kernel`.
+
+RawPtr (%px)
+------------
+
+**Warning**: This exposes the real kernel address and should **only** be used
+for debugging purposes.
+
+**Example**::
+
+    use kernel::ptr::RawPtr;
+
+    pr_info!("Debug pointer: {:p}\n", RawPtr::from(ptr));
+
+Formatting Options
+------------------
+
+All pointer wrapper types support standard Rust formatting options including
+width, alignment, and padding characters. These options are preserved through
+the formatting system.
+
+The following examples demonstrate formatting options using ``RawPtr`` for
+predictable output. The same options work with ``HashedPtr`` and
+``RestrictedPtr``, though the exact output may vary due to pointer hashing::
+
+    use kernel::ptr::RawPtr;
+
+    // Basic formatting
+    pr_info!("Pointer: {:p}\n", RawPtr::from(ptr));
+
+    // Minimum width
+    pr_info!("Pointer: {:30p}\n", RawPtr::from(ptr));
+
+    // Right align with zero padding
+    pr_info!("Pointer: {:0>30p}\n", RawPtr::from(ptr));
+
+    // Left align with zero padding
+    pr_info!("Pointer: {:0<30p}\n", RawPtr::from(ptr));
+
+    // Center align with zero padding
+    pr_info!("Pointer: {:0^30p}\n", RawPtr::from(ptr));
+
+    // Right align with space padding (default)
+    pr_info!("Pointer: {:>30p}\n", RawPtr::from(ptr));
+
+    // Center align with custom padding character
+    pr_info!("Pointer: {:*^30p}\n", RawPtr::from(ptr));
+
+See Also
+--------
+
+- :doc:`../core-api/printk-formats` - General pointer formatting documentation
+- `rust/kernel/ptr.rs <srctree/rust/kernel/ptr.rs>`_ - Implementation
-- 
2.43.0

Re: [PATCH v5 2/4] rust: kernel: Add pointer wrapper types for safe pointer formatting

[Dirk Behme]

On 26.12.25 15:07, Ke Sun wrote:
> Add three pointer wrapper types (HashedPtr, RestrictedPtr, RawPtr) to
> rust/kernel/ptr.rs that correspond to C kernel's printk format specifiers
> %p, %pK, and %px. These types provide type-safe pointer formatting that
> matches C kernel patterns.
> 
> These wrapper types implement core::fmt::Pointer and delegate to the
> corresponding kernel formatting functions, enabling safe pointer
> formatting in Rust code that prevents information leaks about kernel
> memory layout.
> 
> Users can explicitly use these types:
>     pr_info!("{:p}\n", HashedPtr::from(ptr));
>     pr_info!("{:p}\n", RestrictedPtr::from(ptr));
>     pr_info!("{:p}\n", RawPtr::from(ptr));
> 
> Signed-off-by: Ke Sun <sunke@kylinos.cn>
> ---
>  rust/helpers/fmt.c     |  65 +++++++++++
>  rust/helpers/helpers.c |   3 +-
>  rust/kernel/ptr.rs     | 240 ++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 304 insertions(+), 4 deletions(-)
>  create mode 100644 rust/helpers/fmt.c
....
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index 79c72762ad9c4..b6877fe8dafc0 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -27,8 +27,9 @@
>  #include "dma.c"
>  #include "drm.c"
>  #include "err.c"
> -#include "irq.c"
> +#include "fmt.c"
>  #include "fs.c"
> +#include "irq.c"
>  #include "io.c"
>  #include "jump_label.c"
>  #include "kunit.c"
> diff --git a/rust/kernel/ptr.rs b/rust/kernel/ptr.rs
> index e3893ed04049d..ed5069c954146 100644
> --- a/rust/kernel/ptr.rs
> +++ b/rust/kernel/ptr.rs
> @@ -1,11 +1,22 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
>  //! Types and functions to work with pointers and addresses.
> +//!
> +//! This module provides wrapper types for formatting kernel pointers that correspond to the
> +//! C kernel's printk format specifiers `%p`, `%pK`, and `%px`.
>  
> -use core::mem::align_of;
> -use core::num::NonZero;
> +use core::{
> +    fmt,
> +    fmt::Pointer,
> +    mem::align_of,
> +    num::NonZero, //
> +};
>  
> -use crate::build_assert;
> +use crate::{
> +    bindings,
> +    build_assert,
> +    ffi::c_void, //
> +};
>  
>  /// Type representing an alignment, which is always a power of two.
>  ///
> @@ -225,3 +236,226 @@ fn align_up(self, alignment: Alignment) -> Option<Self> {
>  }
>  
>  impl_alignable_uint!(u8, u16, u32, u64, usize);
> +
> +/// Placeholder string used when pointer hashing is not ready yet.
> +const PTR_PLACEHOLDER: &str = if core::mem::size_of::<*const c_void>() == 8 {
> +    "(____ptrval____)"
> +} else {
> +    "(ptrval)"
> +};
> +
> +/// Macro to implement common methods for pointer wrapper types.
> +macro_rules! impl_ptr_wrapper {
> +    ($($name:ident),* $(,)?) => {
> +        $(
> +            impl $name {
> +                /// Creates a new instance from a raw pointer.
> +                #[inline]
> +                pub fn from<T>(ptr: *const T) -> Self {
> +                    Self(ptr.cast())
> +                }
> +
> +                /// Creates a new instance from a mutable raw pointer.
> +                #[inline]
> +                pub fn from_mut<T>(ptr: *mut T) -> Self {
> +                    Self(ptr.cast())
> +                }
> +
> +                /// Returns the inner raw pointer.
> +                #[inline]
> +                pub fn as_ptr(&self) -> *const c_void {
> +                    self.0
> +                }
> +            }
> +
> +            impl<T> From<*const T> for $name {
> +                #[inline]
> +                fn from(ptr: *const T) -> Self {
> +                    Self::from(ptr)
> +                }
> +            }
> +
> +            impl<T> From<*mut T> for $name {
> +                #[inline]
> +                fn from(ptr: *mut T) -> Self {
> +                    Self::from_mut(ptr)
> +                }
> +            }
> +        )*
> +    };
> +}
> +
> +/// Helper function to hash a pointer and format it.
> +///
> +/// Returns `Ok(())` if the hash was successfully computed and formatted,
> +/// or the placeholder string if hashing is not ready yet.
> +fn format_hashed_ptr(ptr: *const c_void, f: &mut fmt::Formatter<'_>) -> fmt::Result {
> +    let mut hashval: crate::ffi::c_ulong = 0;
> +    // SAFETY: We're calling the kernel's ptr_to_hashval function which handles
> +    // hashing. This is safe as long as ptr is a valid pointer value.
> +    let ret = unsafe { bindings::ptr_to_hashval(ptr, core::ptr::addr_of_mut!(hashval)) };
> +
> +    if ret != 0 {
> +        // Hash not ready yet, print placeholder
> +        return f.write_str(PTR_PLACEHOLDER);
> +    }
> +
> +    // Successfully got hash value, format it using Pointer::fmt to preserve
> +    // formatting options (width, alignment, padding, etc.)
> +    Pointer::fmt(&(hashval as *const c_void), f)
> +}
> +
> +/// A pointer that will be hashed when printed (corresponds to `%p`).
> +///
> +/// This is the default behavior for kernel pointers - they are hashed to prevent
> +/// leaking information about the kernel memory layout.
> +///
> +/// # Example
> +///
> +/// ```
> +/// use kernel::{
> +///     prelude::fmt,
> +///     ptr::HashedPtr,
> +///     str::CString, //
> +/// };
> +///
> +/// let ptr = HashedPtr::from(0x12345678 as *const u8);
> +/// pr_info!("Hashed pointer: {:016p}\n", ptr);
> +///
> +/// // Width option test
> +/// let cstr = CString::try_from_fmt(fmt!("{:30p}", ptr))?;
> +/// let width_30 = cstr.to_str()?;
> +/// assert_eq!(width_30.len(), 30);
> +/// # Ok::<(), kernel::error::Error>(())
> +/// ```


Is this intended?

[    1.932037]     # rust_doctest_kernel_ptr_rs_6.location:
rust/kernel/ptr.rs:315
[    1.932322] rust_doctests_kernel: Hashed pointer: (____ptrval____)
[    1.933032]     # rust_doctest_kernel_ptr_rs_6: ASSERTION FAILED at
rust/kernel/ptr.rs:329
[    1.933032]     Expected width_30.len() == 30 to be true, but is false
[    1.933892]     not ok 179 rust_doctest_kernel_ptr_rs_6


[    1.934097]     # rust_doctest_kernel_ptr_rs_7.location:
rust/kernel/ptr.rs:353
[    1.934434] rust_doctests_kernel: Restricted pointer: (____ptrval____)
[    1.934707]     # rust_doctest_kernel_ptr_rs_7: ASSERTION FAILED at
rust/kernel/ptr.rs:367
[    1.934707]     Expected width_30.len() == 30 to be true, but is false
[    1.935156]     not ok 180 rust_doctest_kernel_ptr_rs_7

This is v5 on top of v6.19-rc1 with x86_64_defconfig booting on QEMU.

Cheers

Dirk

Re: [PATCH v5 2/4] rust: kernel: Add pointer wrapper types for safe pointer formatting

[Ke Sun]

Dirk Behme <dirk.behme@gmail.com> 于2025年12月26日周五 23:10写道：
>
> On 26.12.25 15:07, Ke Sun wrote:
> > Add three pointer wrapper types (HashedPtr, RestrictedPtr, RawPtr) to
> > rust/kernel/ptr.rs that correspond to C kernel's printk format specifiers
> > %p, %pK, and %px. These types provide type-safe pointer formatting that
> > matches C kernel patterns.
> >
> > These wrapper types implement core::fmt::Pointer and delegate to the
> > corresponding kernel formatting functions, enabling safe pointer
> > formatting in Rust code that prevents information leaks about kernel
> > memory layout.
> >
> > Users can explicitly use these types:
> >     pr_info!("{:p}\n", HashedPtr::from(ptr));
> >     pr_info!("{:p}\n", RestrictedPtr::from(ptr));
> >     pr_info!("{:p}\n", RawPtr::from(ptr));
> >
> > Signed-off-by: Ke Sun <sunke@kylinos.cn>
> > ---
> >  rust/helpers/fmt.c     |  65 +++++++++++
> >  rust/helpers/helpers.c |   3 +-
> >  rust/kernel/ptr.rs     | 240 ++++++++++++++++++++++++++++++++++++++++-
> >  3 files changed, 304 insertions(+), 4 deletions(-)
> >  create mode 100644 rust/helpers/fmt.c
> ....
> > diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> > index 79c72762ad9c4..b6877fe8dafc0 100644
> > --- a/rust/helpers/helpers.c
> > +++ b/rust/helpers/helpers.c
> > @@ -27,8 +27,9 @@
> >  #include "dma.c"
> >  #include "drm.c"
> >  #include "err.c"
> > -#include "irq.c"
> > +#include "fmt.c"
> >  #include "fs.c"
> > +#include "irq.c"
> >  #include "io.c"
> >  #include "jump_label.c"
> >  #include "kunit.c"
> > diff --git a/rust/kernel/ptr.rs b/rust/kernel/ptr.rs
> > index e3893ed04049d..ed5069c954146 100644
> > --- a/rust/kernel/ptr.rs
> > +++ b/rust/kernel/ptr.rs
> > @@ -1,11 +1,22 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >
> >  //! Types and functions to work with pointers and addresses.
> > +//!
> > +//! This module provides wrapper types for formatting kernel pointers that correspond to the
> > +//! C kernel's printk format specifiers `%p`, `%pK`, and `%px`.
> >
> > -use core::mem::align_of;
> > -use core::num::NonZero;
> > +use core::{
> > +    fmt,
> > +    fmt::Pointer,
> > +    mem::align_of,
> > +    num::NonZero, //
> > +};
> >
> > -use crate::build_assert;
> > +use crate::{
> > +    bindings,
> > +    build_assert,
> > +    ffi::c_void, //
> > +};
> >
> >  /// Type representing an alignment, which is always a power of two.
> >  ///
> > @@ -225,3 +236,226 @@ fn align_up(self, alignment: Alignment) -> Option<Self> {
> >  }
> >
> >  impl_alignable_uint!(u8, u16, u32, u64, usize);
> > +
> > +/// Placeholder string used when pointer hashing is not ready yet.
> > +const PTR_PLACEHOLDER: &str = if core::mem::size_of::<*const c_void>() == 8 {
> > +    "(____ptrval____)"
> > +} else {
> > +    "(ptrval)"
> > +};
> > +
> > +/// Macro to implement common methods for pointer wrapper types.
> > +macro_rules! impl_ptr_wrapper {
> > +    ($($name:ident),* $(,)?) => {
> > +        $(
> > +            impl $name {
> > +                /// Creates a new instance from a raw pointer.
> > +                #[inline]
> > +                pub fn from<T>(ptr: *const T) -> Self {
> > +                    Self(ptr.cast())
> > +                }
> > +
> > +                /// Creates a new instance from a mutable raw pointer.
> > +                #[inline]
> > +                pub fn from_mut<T>(ptr: *mut T) -> Self {
> > +                    Self(ptr.cast())
> > +                }
> > +
> > +                /// Returns the inner raw pointer.
> > +                #[inline]
> > +                pub fn as_ptr(&self) -> *const c_void {
> > +                    self.0
> > +                }
> > +            }
> > +
> > +            impl<T> From<*const T> for $name {
> > +                #[inline]
> > +                fn from(ptr: *const T) -> Self {
> > +                    Self::from(ptr)
> > +                }
> > +            }
> > +
> > +            impl<T> From<*mut T> for $name {
> > +                #[inline]
> > +                fn from(ptr: *mut T) -> Self {
> > +                    Self::from_mut(ptr)
> > +                }
> > +            }
> > +        )*
> > +    };
> > +}
> > +
> > +/// Helper function to hash a pointer and format it.
> > +///
> > +/// Returns `Ok(())` if the hash was successfully computed and formatted,
> > +/// or the placeholder string if hashing is not ready yet.
> > +fn format_hashed_ptr(ptr: *const c_void, f: &mut fmt::Formatter<'_>) -> fmt::Result {
> > +    let mut hashval: crate::ffi::c_ulong = 0;
> > +    // SAFETY: We're calling the kernel's ptr_to_hashval function which handles
> > +    // hashing. This is safe as long as ptr is a valid pointer value.
> > +    let ret = unsafe { bindings::ptr_to_hashval(ptr, core::ptr::addr_of_mut!(hashval)) };
> > +
> > +    if ret != 0 {
> > +        // Hash not ready yet, print placeholder
> > +        return f.write_str(PTR_PLACEHOLDER);

Can you try `return f.pad(PTR_PLACEHOLDER);`? I'm testing it.

> > +    }
> > +
> > +    // Successfully got hash value, format it using Pointer::fmt to preserve
> > +    // formatting options (width, alignment, padding, etc.)
> > +    Pointer::fmt(&(hashval as *const c_void), f)
> > +}
> > +
> > +/// A pointer that will be hashed when printed (corresponds to `%p`).
> > +///
> > +/// This is the default behavior for kernel pointers - they are hashed to prevent
> > +/// leaking information about the kernel memory layout.
> > +///
> > +/// # Example
> > +///
> > +/// ```
> > +/// use kernel::{
> > +///     prelude::fmt,
> > +///     ptr::HashedPtr,
> > +///     str::CString, //
> > +/// };
> > +///
> > +/// let ptr = HashedPtr::from(0x12345678 as *const u8);
> > +/// pr_info!("Hashed pointer: {:016p}\n", ptr);
> > +///
> > +/// // Width option test
> > +/// let cstr = CString::try_from_fmt(fmt!("{:30p}", ptr))?;
> > +/// let width_30 = cstr.to_str()?;
> > +/// assert_eq!(width_30.len(), 30);
> > +/// # Ok::<(), kernel::error::Error>(())
> > +/// ```
>
>
> Is this intended?
>
> [    1.932037]     # rust_doctest_kernel_ptr_rs_6.location:
> rust/kernel/ptr.rs:315
> [    1.932322] rust_doctests_kernel: Hashed pointer: (____ptrval____)
> [    1.933032]     # rust_doctest_kernel_ptr_rs_6: ASSERTION FAILED at
> rust/kernel/ptr.rs:329
> [    1.933032]     Expected width_30.len() == 30 to be true, but is false
> [    1.933892]     not ok 179 rust_doctest_kernel_ptr_rs_6
>
>
> [    1.934097]     # rust_doctest_kernel_ptr_rs_7.location:
> rust/kernel/ptr.rs:353
> [    1.934434] rust_doctests_kernel: Restricted pointer: (____ptrval____)
> [    1.934707]     # rust_doctest_kernel_ptr_rs_7: ASSERTION FAILED at
> rust/kernel/ptr.rs:367

// lib/vsprintf.c
static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
{
unsigned long hashval;

if (!READ_ONCE(filled_random_ptr_key))   // filled_random_ptr_key might be false
return -EBUSY;

> [    1.934707]     Expected width_30.len() == 30 to be true, but is false
> [    1.935156]     not ok 180 rust_doctest_kernel_ptr_rs_7
>
> This is v5 on top of v6.19-rc1 with x86_64_defconfig booting on QEMU.
>
> Cheers
>
> Dirk