linux-kernel - [PATCH v3 7/7] rust: alloc: add Vec::insert_within

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250422-vec-methods-v3-7-deff5eea568a@google.com>
Date: Tue, 22 Apr 2025 09:52:22 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Matthew Maurer <mmaurer@...gle.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v3 7/7] rust: alloc: add Vec::insert_within_capacity

This adds a variant of Vec::insert that does not allocate memory. This
makes it safe to use this function while holding a spinlock. Rust Binder
uses it for the range allocator fast path.

Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/alloc/kvec.rs | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index 2f28fda793e13841b59e83f34681e71ac815aff2..d96de01a7ab3c808f5aded067ad6f1e3ba8029ce 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -355,6 +355,45 @@ pub unsafe fn push_within_capacity_unchecked(&mut self, v: T) {
         unsafe { self.inc_len(1) };
     }
 
+    /// Inserts an element at the given index in the [`Vec`] instance.
+    ///
+    /// Fails if the vector does not have capacity for the new element. Panics if the index is out
+    /// of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = KVec::with_capacity(10, GFP_KERNEL);
+    /// for i in 0..10 {
+    ///     v.push_within_capacity(i).unwrap();
+    /// }
+    ///
+    /// assert!(v.push_within_capacity(10).is_err());
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn insert_within_capacity(&mut self, index: usize, element: T) -> Result<(), T> {
+        let len = self.len();
+        assert!(index <= len);
+
+        if len >= self.capacity() {
+            return Err(element);
+        }
+
+        // SAFETY: This is in bounds since `index <= len < capacity`.
+        let p = unsafe { self.as_mut_ptr().add(index) };
+        // INVARIANT: This breaks the Vec invariants by making `index` contain an invalid element,
+        // but we restore the invariants below.
+        // SAFETY: Both the src and dst ranges end no later than one element after the length.
+        // Since the length is less than the capacity, both ranges are in bounds of the allocation.
+        unsafe { ptr::copy(p, p.add(1), len - index) };
+        // INVARIANT: This restores the Vec invariants.
+        // SAFETY: The pointer is in-bounds of the allocation.
+        unsafe { ptr::write(p, element) };
+        // SAFETY: Index `len` contains a valid element due to the above copy and write.
+        unsafe { self.inc_len(1) };
+        Ok(())
+    }
+
     /// Removes the last element from a vector and returns it, or `None` if it is empty.
     ///
     /// # Examples

-- 
2.49.0.805.g082f7c87e0-goog