kernel: dev: Add /dev/random

Introduce a prototype cryptographically secure (?) random number generator.

The RNG uses ChaCha20 seeded with a SipHash-processed entropy pool. Entropy is
collected only at read time and is mixed into the internal pool before each
ChaCha20 reseed. The design is still experimental.

Signed-off-by: Alex Funo <frost@osmora.org>
Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 88 insertions, 0 deletions

diff --git a/sys/dev/random/random.c b/sys/dev/random/random.c
new file mode 100644
index 0000000..d79df69
--- /dev/null
+++ b/sys/dev/random/random.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/sio.h>
+#include <sys/device.h>
+#include <sys/driver.h>
+#include <dev/random/chacha20.h>
+#include <dev/random/siphash.h>
+#include <dev/random/entropy.h>
+#include <fs/devfs.h>
+#include <string.h>
+
+static struct cdevsw random_cdevsw;
+static struct entropy_pool entropy;
+
+uint8_t key[32] = {0};
+uint8_t nonce[12] = {0};
+uint32_t state[16];
+uint32_t tsc;
+
+static inline uint64_t
+read_tsc(void)
+{
+    uint32_t lo, hi;
+    __asm__ volatile ("rdtsc" : "=a"(lo), "=d"(hi));
+    return ((uint64_t)hi << 32) | lo;
+}
+
+static int
+random_read(dev_t dev, struct sio_txn *sio, int flags)
+{
+    tsc = read_tsc();
+    mix_entropy(&entropy, (uint8_t *)&tsc, sizeof(tsc), 1);
+
+    chacha20_init(state, entropy.pool, nonce, 0);
+    chacha20_encrypt(state, NULL, sio->buf, sio->len);
+
+    return sio->len;
+}
+
+static int
+random_init(void)
+{
+    char devname[] = "random";
+    devmajor_t major;
+    dev_t dev;
+
+    /* Register the device here */
+    major = dev_alloc_major();
+    dev = dev_alloc(major);
+    dev_register(major, dev, &random_cdevsw);
+    devfs_create_entry(devname, major, dev, 0444);
+
+    return 0;
+}
+
+static struct cdevsw random_cdevsw = {
+    .read = random_read,
+    .write = nowrite
+};
+
+DRIVER_EXPORT(random_init, "random");