*RFL import: kernel::user_ptr

Commit reference: 3dfc5eb

Author: hoshinolina

rust/helpers/uaccess.c

@@ -2,6 +2,11 @@
 
 #include <linux/uaccess.h>
 
+unsigned long rust_helper_clear_user(void __user *to, unsigned long n)
+{
+	return clear_user(to, n);
+}
+
 unsigned long rust_helper_copy_from_user(void *to, const void __user *from,
 					 unsigned long n)
 {

rust/kernel/lib.rs

@@ -79,6 +79,7 @@ pub mod time;
 pub mod transmute;
 pub mod types;
 pub mod uaccess;
+pub mod user_ptr;
 pub mod workqueue;
 pub mod xarray;
 

rust/kernel/user_ptr.rs

@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! User pointers.
+//!
+//! C header: [`include/linux/uaccess.h`](../../../../include/linux/uaccess.h)
+
+use crate::{
+    bindings,
+    error::code::*,
+    error::Result,
+    io_buffer::{IoBufferReader, IoBufferWriter},
+};
+use alloc::vec::Vec;
+
+/// A reference to an area in userspace memory, which can be either
+/// read-only or read-write.
+///
+/// All methods on this struct are safe: invalid pointers return
+/// `EFAULT`. Concurrent access, *including data races to/from userspace
+/// memory*, is permitted, because fundamentally another userspace
+/// thread/process could always be modifying memory at the same time
+/// (in the same way that userspace Rust's [`std::io`] permits data races
+/// with the contents of files on disk). In the presence of a race, the
+/// exact byte values read/written are unspecified but the operation is
+/// well-defined. Kernelspace code should validate its copy of data
+/// after completing a read, and not expect that multiple reads of the
+/// same address will return the same value.
+///
+/// All APIs enforce the invariant that a given byte of memory from userspace
+/// may only be read once. By preventing double-fetches we avoid TOCTOU
+/// vulnerabilities. This is accomplished by taking `self` by value to prevent
+/// obtaining multiple readers on a given [`UserSlicePtr`], and the readers
+/// only permitting forward reads.
+///
+/// Constructing a [`UserSlicePtr`] performs no checks on the provided
+/// address and length, it can safely be constructed inside a kernel thread
+/// with no current userspace process. Reads and writes wrap the kernel APIs
+/// `copy_from_user` and `copy_to_user`, which check the memory map of the
+/// current process and enforce that the address range is within the user
+/// range (no additional calls to `access_ok` are needed).
+///
+/// [`std::io`]: https://doc.rust-lang.org/std/io/index.html
+pub struct UserSlicePtr(*mut core::ffi::c_void, usize);
+
+impl UserSlicePtr {
+    /// Constructs a user slice from a raw pointer and a length in bytes.
+    ///
+    /// # Safety
+    ///
+    /// Callers must be careful to avoid time-of-check-time-of-use
+    /// (TOCTOU) issues. The simplest way is to create a single instance of
+    /// [`UserSlicePtr`] per user memory block as it reads each byte at
+    /// most once.
+    pub unsafe fn new(ptr: *mut core::ffi::c_void, length: usize) -> Self {
+        UserSlicePtr(ptr, length)
+    }
+
+    /// Reads the entirety of the user slice.
+    ///
+    /// Returns `EFAULT` if the address does not currently point to
+    /// mapped, readable memory.
+    pub fn read_all(self) -> Result<Vec<u8>> {
+        self.reader().read_all()
+    }
+
+    /// Constructs a [`UserSlicePtrReader`].
+    pub fn reader(self) -> UserSlicePtrReader {
+        UserSlicePtrReader(self.0, self.1)
+    }
+
+    /// Writes the provided slice into the user slice.
+    ///
+    /// Returns `EFAULT` if the address does not currently point to
+    /// mapped, writable memory (in which case some data from before the
+    /// fault may be written), or `data` is larger than the user slice
+    /// (in which case no data is written).
+    pub fn write_all(self, data: &[u8]) -> Result {
+        self.writer().write_slice(data)
+    }
+
+    /// Constructs a [`UserSlicePtrWriter`].
+    pub fn writer(self) -> UserSlicePtrWriter {
+        UserSlicePtrWriter(self.0, self.1)
+    }
+
+    /// Constructs both a [`UserSlicePtrReader`] and a [`UserSlicePtrWriter`].
+    pub fn reader_writer(self) -> (UserSlicePtrReader, UserSlicePtrWriter) {
+        (
+            UserSlicePtrReader(self.0, self.1),
+            UserSlicePtrWriter(self.0, self.1),
+        )
+    }
+}
+
+/// A reader for [`UserSlicePtr`].
+///
+/// Used to incrementally read from the user slice.
+pub struct UserSlicePtrReader(*mut core::ffi::c_void, usize);
+
+impl IoBufferReader for UserSlicePtrReader {
+    /// Returns the number of bytes left to be read from this.
+    ///
+    /// Note that even reading less than this number of bytes may fail.
+    fn len(&self) -> usize {
+        self.1
+    }
+
+    /// Reads raw data from the user slice into a raw kernel buffer.
+    ///
+    /// # Safety
+    ///
+    /// The output buffer must be valid.
+    unsafe fn read_raw(&mut self, out: *mut u8, len: usize) -> Result {
+        if len > self.1 || len > u32::MAX as usize {
+            return Err(EFAULT);
+        }
+        let res = unsafe { bindings::copy_from_user(out as _, self.0, len as _) };
+        if res != 0 {
+            return Err(EFAULT);
+        }
+        // Since this is not a pointer to a valid object in our program,
+        // we cannot use `add`, which has C-style rules for defined
+        // behavior.
+        self.0 = self.0.wrapping_add(len);
+        self.1 -= len;
+        Ok(())
+    }
+}
+
+/// A writer for [`UserSlicePtr`].
+///
+/// Used to incrementally write into the user slice.
+pub struct UserSlicePtrWriter(*mut core::ffi::c_void, usize);
+
+impl IoBufferWriter for UserSlicePtrWriter {
+    fn len(&self) -> usize {
+        self.1
+    }
+
+    fn clear(&mut self, mut len: usize) -> Result {
+        let mut ret = Ok(());
+        if len > self.1 {
+            ret = Err(EFAULT);
+            len = self.1;
+        }
+
+        // SAFETY: The buffer will be validated by `clear_user`. We ensure that `len` is within
+        // bounds in the check above.
+        let left = unsafe { bindings::clear_user(self.0, len as _) } as usize;
+        if left != 0 {
+            ret = Err(EFAULT);
+            len -= left;
+        }
+
+        self.0 = self.0.wrapping_add(len);
+        self.1 -= len;
+        ret
+    }
+
+    unsafe fn write_raw(&mut self, data: *const u8, len: usize) -> Result {
+        if len > self.1 || len > u32::MAX as usize {
+            return Err(EFAULT);
+        }
+        let res = unsafe { bindings::copy_to_user(self.0, data as _, len as _) };
+        if res != 0 {
+            return Err(EFAULT);
+        }
+        // Since this is not a pointer to a valid object in our program,
+        // we cannot use `add`, which has C-style rules for defined
+        // behavior.
+        self.0 = self.0.wrapping_add(len);
+        self.1 -= len;
+        Ok(())
+    }
+}