linux-kernel - [PATCH v2] rust: Add support for feeding entropy to randomness pool

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Message-ID: <20251216-add-entropy-v2-1-4d866f251474@google.com>
Date: Tue, 16 Dec 2025 00:37:15 +0000
From: Matthew Maurer <mmaurer@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	Matthew Maurer <mmaurer@...gle.com>
Subject: [PATCH v2] rust: Add support for feeding entropy to randomness pool

Adds just enough support to allow device drivers to feed entropy to the
central pool.

Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
---
Changes in v2:
- Added more details in the docs about the API, specifically about it
  not crediting entropy and when it ought to be used.
- Link to v1: https://lore.kernel.org/r/20251212-add-entropy-v1-1-e70ad1bc9c65@google.com
---
 rust/kernel/lib.rs  |  1 +
 rust/kernel/rand.rs | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index f812cf12004286962985a068665443dc22c389a2..bf64752d276b0bdea06ac0de8a5e219190129377 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -130,6 +130,7 @@
 pub mod ptr;
 #[cfg(CONFIG_RUST_PWM_ABSTRACTIONS)]
 pub mod pwm;
+pub mod rand;
 pub mod rbtree;
 pub mod regulator;
 pub mod revocable;
diff --git a/rust/kernel/rand.rs b/rust/kernel/rand.rs
new file mode 100644
index 0000000000000000000000000000000000000000..abaafa12c6ec7fe600463dfc2bdb78385a09cc52
--- /dev/null
+++ b/rust/kernel/rand.rs
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Randomness.
+//!
+//! C header: [`include/linux/random.h`](../../../../include/linux/random.h)
+
+use crate::bindings;
+use crate::ffi::c_void;
+
+/// Adds the given buffer to the entropy pool, but does not credit any entropy.
+///
+/// This is intended for use mixing in data that is likely to differ between devices or boots, but
+/// may otherwise be predictable. Examples include MAC addresses or RTC values. This slightly
+/// improves randomness in entropy-constrained environments (especially common for embedded
+/// devices).
+pub fn add_device_randomness(buf: &[u8]) {
+    // SAFETY: We just need the pointer to be valid for the length, which a slice provides.
+    unsafe { bindings::add_device_randomness(buf.as_ptr().cast::<c_void>(), buf.len()) };
+}

---
base-commit: 008d3547aae5bc86fac3eda317489169c3fda112
change-id: 20251029-add-entropy-f57e12ebe110

Best regards,
-- 
Matthew Maurer <mmaurer@...gle.com>