[dev][virtio-rng] Introduce virtio-rng driver to seed system prng

dev/virtio/rng/include/dev/virtio/rng.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2026 Kuan-Wei Chiu <visitorckw@gmail.com>
+ *
+ * Use of this source code is governed by a MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT
+ */
+#pragma once
+
+#include <lk/err.h>
+
+struct virtio_device;
+
+status_t virtio_rng_init(virtio_device *dev);
+ssize_t virtio_rng_read(void *buf, size_t len);

dev/virtio/rng/rules.mk

@@ -0,0 +1,8 @@
+LOCAL_DIR := $(GET_LOCAL_DIR)
+
+MODULE := $(LOCAL_DIR)
+
+MODULE_SRCS += \
+    $(LOCAL_DIR)/virtio-rng.cpp
+
+include make/module.mk

dev/virtio/rng/virtio-rng.cpp

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2026 Kuan-Wei Chiu <visitorckw@gmail.com>
+ *
+ * Use of this source code is governed by a MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT
+ */
+
+#include <dev/virtio/rng.h>
+#include <dev/virtio/virtio-device.h>
+#include <dev/virtio/virtio_ring.h>
+#include <kernel/thread.h>
+#include <kernel/vm.h>
+#include <lk/debug.h>
+#include <lk/err.h>
+#include <lk/init.h>
+#include <lk/trace.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define LOCAL_TRACE 0
+
+constexpr uint16_t RNG_QUEUE_INDEX = 0;
+
+struct virtio_rng_state {
+    virtio_device *dev;
+    bool initialized;
+    volatile size_t last_rx_len;
+};
+
+static virtio_rng_state rng;
+
+static enum handler_return virtio_rng_irq(virtio_device *dev, uint ring_index, const vring_used_elem *e) {
+    if (ring_index == RNG_QUEUE_INDEX && e)
+        rng.last_rx_len = e->len;
+
+    return INT_NO_RESCHEDULE;
+}
+
+status_t virtio_rng_init(virtio_device *dev) {
+    LTRACE_ENTRY;
+
+    rng.dev = dev;
+    rng.initialized = false;
+    rng.last_rx_len = 0;
+
+    dev->set_irq_callbacks(virtio_rng_irq, nullptr);
+
+    status_t err = dev->virtio_alloc_ring(RNG_QUEUE_INDEX, 32);
+    if (err != NO_ERROR) {
+        TRACEF("virtio-rng: Failed to allocate virtqueue\n");
+        return err;
+    }
+
+    dev->bus()->virtio_status_driver_ok();
+    rng.initialized = true;
+
+    LTRACEF("virtio-rng: initialized successfully\n");
+    return NO_ERROR;
+}
+
+ssize_t virtio_rng_read(void *buf, size_t len) {
+    if (!rng.initialized || len == 0) return ERR_NOT_CONFIGURED;
+
+    vaddr_t v_start = (vaddr_t)buf;
+    vaddr_t v_end = v_start + len - 1;
+    if ((v_start / PAGE_SIZE) != (v_end / PAGE_SIZE))
+        return ERR_INVALID_ARGS;
+
+    paddr_t paddr = vaddr_to_paddr(buf);
+    if (!paddr) return ERR_INVALID_ARGS;
+
+    uint16_t desc_idx = rng.dev->virtio_alloc_desc(RNG_QUEUE_INDEX);
+    if (desc_idx == 0xffff) return ERR_NO_MEMORY;
+
+    vring_desc *desc = rng.dev->virtio_desc_index_to_desc(RNG_QUEUE_INDEX, desc_idx);
+    desc->addr = paddr;
+    desc->len = (uint32_t)len;
+    desc->flags = VRING_DESC_F_WRITE;
+
+    rng.last_rx_len = 0;
+    rng.dev->virtio_submit_chain(RNG_QUEUE_INDEX, desc_idx);
+    rng.dev->bus()->virtio_kick(RNG_QUEUE_INDEX);
+
+    while (rng.last_rx_len == 0) {
+        rng.dev->handle_queue_interrupt();
+        thread_yield();
+    }
+
+    size_t rx_len = rng.last_rx_len;
+    rng.last_rx_len = 0;
+
+    rng.dev->virtio_free_desc(RNG_QUEUE_INDEX, desc_idx);
+    return rx_len; 
+}
+
+static void seed_system_prng(uint level) {
+    unsigned int seed = 0;
+    ssize_t bytes_read;
+
+    if (!rng.initialized)
+        return;
+
+    bytes_read = virtio_rng_read(&seed, sizeof(seed));
+
+    if (bytes_read == sizeof(seed)) {
+        srand(seed);
+        dprintf(INFO, "virtio-rng: System PRNG seeded with hardware entropy\n");
+    } else {
+        dprintf(INFO, "virtio-rng: Failed to seed system PRNG\n");
+    }
+}
+
+LK_INIT_HOOK(virtio_rng_seed, seed_system_prng, LK_INIT_LEVEL_TARGET + 1);

dev/virtio/virtio-mmio-bus.cpp

@@ -34,6 +34,9 @@
 #if WITH_DEV_VIRTIO_9P
 #include <dev/virtio/9p.h>
 #endif
+#if WITH_DEV_VIRTIO_RNG
+#include <dev/virtio/rng.h>
+#endif
 
 #define LOCAL_TRACE 0
 
@@ -237,6 +240,16 @@ int virtio_mmio_detect(void *ptr, uint count, const uint irqs[], size_t stride)
             }
         }
 #endif // WITH_DEV_VIRTIO_NET
+#if WITH_DEV_VIRTIO_RNG
+        if (mmio->device_id == 4) { // virtio-rng
+            LTRACEF("found rng device\n");
+
+            status_t err = virtio_rng_init(dev);
+            if (err >= 0) {
+                found++;
+            }
+        }
+#endif // WITH_DEV_VIRTIO_RNG
 #if WITH_DEV_VIRTIO_9P
         if (mmio->device_id == 9) { // 9p device
             LTRACEF("found 9p device\n");

dev/virtio/virtio-pci-bus.cpp

@@ -32,6 +32,9 @@
 #if WITH_DEV_VIRTIO_GPU
 #include <dev/virtio/gpu.h>
 #endif
+#if WITH_DEV_VIRTIO_RNG
+#include <dev/virtio/rng.h>
+#endif
 
 #define LOCAL_TRACE 0
 
@@ -465,17 +468,45 @@ static status_t init_gpu(pci_location_t loc, const virtio_pci_devices &dev_table
 #endif
 }
 
+static status_t init_rng(pci_location_t loc, const virtio_pci_devices &dev_table_entry, size_t index) {
+    LTRACE_ENTRY;
+
+#if WITH_DEV_VIRTIO_RNG
+    auto *bus = new virtio_pci_bus();
+    auto *dev = new virtio_device(bus);
+
+    auto err = bus->init(dev, loc, index);
+    if (err != NO_ERROR) {
+        delete bus;
+        return err;
+    }
+
+    dev->set_config_ptr(bus->device_config());
+
+    err = virtio_rng_init(dev);
+    if (err != NO_ERROR) {
+        PANIC_UNIMPLEMENTED;
+    }
+
+    return err;
+#else
+    return ERR_NOT_FOUND;
+#endif
+}
+
 
 int virtio_pci_init() {
     LTRACE_ENTRY;
 
     constexpr virtio_pci_devices devices[] = {
         { 0x1000, true, &init_net }, // transitional network
         { 0x1001, true, &init_block }, // transitional block
+        { 0x1005, true, &init_rng }, // transitional rng
         { 0x1009, true, nullptr }, // legacy virtio 9p
         { 0x1041, false, &init_net }, // non-transitional network
         { 0x1042, false, &init_block }, // non-transitional block
         { 0x1043, false, nullptr }, // non-transitional console
+        { 0x1044, false, &init_rng }, // non-transitional rng
         { 0x1050, false, &init_gpu }, // non-transitional gpu
         { 0x1052, false, nullptr }, // non-transitional input
     };

platform/qemu-virt-arm/rules.mk

@@ -34,6 +34,7 @@ MODULE_DEPS += \
     dev/virtio/block \
     dev/virtio/gpu \
     dev/virtio/net \
+    dev/virtio/rng \
     lib/cbuf \
     lib/fdtwalk \
     lib/fs/9p \