1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Randomness driver for virtio 4 * Copyright (C) 2007, 2008 Rusty Russell IBM Corporation 5 */ 6 7 #include <linux/err.h> 8 #include <linux/hw_random.h> 9 #include <linux/scatterlist.h> 10 #include <linux/spinlock.h> 11 #include <linux/virtio.h> 12 #include <linux/virtio_rng.h> 13 #include <linux/module.h> 14 #include <linux/slab.h> 15 16 static DEFINE_IDA(rng_index_ida); 17 18 struct virtrng_info { 19 struct hwrng hwrng; 20 struct virtqueue *vq; 21 char name[25]; 22 int index; 23 bool hwrng_register_done; 24 bool hwrng_removed; 25 /* data transfer */ 26 struct completion have_data; 27 unsigned int data_avail; 28 unsigned int data_idx; 29 /* minimal size returned by rng_buffer_size() */ 30 #if SMP_CACHE_BYTES < 32 31 u8 data[32]; 32 #else 33 u8 data[SMP_CACHE_BYTES]; 34 #endif 35 }; 36 37 static void random_recv_done(struct virtqueue *vq) 38 { 39 struct virtrng_info *vi = vq->vdev->priv; 40 41 /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */ 42 if (!virtqueue_get_buf(vi->vq, &vi->data_avail)) 43 return; 44 45 vi->data_idx = 0; 46 47 complete(&vi->have_data); 48 } 49 50 static void request_entropy(struct virtrng_info *vi) 51 { 52 struct scatterlist sg; 53 54 reinit_completion(&vi->have_data); 55 vi->data_avail = 0; 56 vi->data_idx = 0; 57 58 sg_init_one(&sg, vi->data, sizeof(vi->data)); 59 60 /* There should always be room for one buffer. */ 61 virtqueue_add_inbuf(vi->vq, &sg, 1, vi->data, GFP_KERNEL); 62 63 virtqueue_kick(vi->vq); 64 } 65 66 static unsigned int copy_data(struct virtrng_info *vi, void *buf, 67 unsigned int size) 68 { 69 size = min_t(unsigned int, size, vi->data_avail); 70 memcpy(buf, vi->data + vi->data_idx, size); 71 vi->data_idx += size; 72 vi->data_avail -= size; 73 if (vi->data_avail == 0) 74 request_entropy(vi); 75 return size; 76 } 77 78 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait) 79 { 80 int ret; 81 struct virtrng_info *vi = (struct virtrng_info *)rng->priv; 82 unsigned int chunk; 83 size_t read; 84 85 if (vi->hwrng_removed) 86 return -ENODEV; 87 88 read = 0; 89 90 /* copy available data */ 91 if (vi->data_avail) { 92 chunk = copy_data(vi, buf, size); 93 size -= chunk; 94 read += chunk; 95 } 96 97 if (!wait) 98 return read; 99 100 /* We have already copied available entropy, 101 * so either size is 0 or data_avail is 0 102 */ 103 while (size != 0) { 104 /* data_avail is 0 but a request is pending */ 105 ret = wait_for_completion_killable(&vi->have_data); 106 if (ret < 0) 107 return ret; 108 /* if vi->data_avail is 0, we have been interrupted 109 * by a cleanup, but buffer stays in the queue 110 */ 111 if (vi->data_avail == 0) 112 return read; 113 114 chunk = copy_data(vi, buf + read, size); 115 size -= chunk; 116 read += chunk; 117 } 118 119 return read; 120 } 121 122 static void virtio_cleanup(struct hwrng *rng) 123 { 124 struct virtrng_info *vi = (struct virtrng_info *)rng->priv; 125 126 complete(&vi->have_data); 127 } 128 129 static int probe_common(struct virtio_device *vdev) 130 { 131 int err, index; 132 struct virtrng_info *vi = NULL; 133 134 vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL); 135 if (!vi) 136 return -ENOMEM; 137 138 vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL); 139 if (index < 0) { 140 err = index; 141 goto err_ida; 142 } 143 sprintf(vi->name, "virtio_rng.%d", index); 144 init_completion(&vi->have_data); 145 146 vi->hwrng = (struct hwrng) { 147 .read = virtio_read, 148 .cleanup = virtio_cleanup, 149 .priv = (unsigned long)vi, 150 .name = vi->name, 151 .quality = 1000, 152 }; 153 vdev->priv = vi; 154 155 /* We expect a single virtqueue. */ 156 vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input"); 157 if (IS_ERR(vi->vq)) { 158 err = PTR_ERR(vi->vq); 159 goto err_find; 160 } 161 162 virtio_device_ready(vdev); 163 164 /* we always have a pending entropy request */ 165 request_entropy(vi); 166 167 return 0; 168 169 err_find: 170 ida_simple_remove(&rng_index_ida, index); 171 err_ida: 172 kfree(vi); 173 return err; 174 } 175 176 static void remove_common(struct virtio_device *vdev) 177 { 178 struct virtrng_info *vi = vdev->priv; 179 180 vi->hwrng_removed = true; 181 vi->data_avail = 0; 182 vi->data_idx = 0; 183 complete(&vi->have_data); 184 if (vi->hwrng_register_done) 185 hwrng_unregister(&vi->hwrng); 186 virtio_reset_device(vdev); 187 vdev->config->del_vqs(vdev); 188 ida_simple_remove(&rng_index_ida, vi->index); 189 kfree(vi); 190 } 191 192 static int virtrng_probe(struct virtio_device *vdev) 193 { 194 return probe_common(vdev); 195 } 196 197 static void virtrng_remove(struct virtio_device *vdev) 198 { 199 remove_common(vdev); 200 } 201 202 static void virtrng_scan(struct virtio_device *vdev) 203 { 204 struct virtrng_info *vi = vdev->priv; 205 int err; 206 207 err = hwrng_register(&vi->hwrng); 208 if (!err) 209 vi->hwrng_register_done = true; 210 } 211 212 #ifdef CONFIG_PM_SLEEP 213 static int virtrng_freeze(struct virtio_device *vdev) 214 { 215 remove_common(vdev); 216 return 0; 217 } 218 219 static int virtrng_restore(struct virtio_device *vdev) 220 { 221 int err; 222 223 err = probe_common(vdev); 224 if (!err) { 225 struct virtrng_info *vi = vdev->priv; 226 227 /* 228 * Set hwrng_removed to ensure that virtio_read() 229 * does not block waiting for data before the 230 * registration is complete. 231 */ 232 vi->hwrng_removed = true; 233 err = hwrng_register(&vi->hwrng); 234 if (!err) { 235 vi->hwrng_register_done = true; 236 vi->hwrng_removed = false; 237 } 238 } 239 240 return err; 241 } 242 #endif 243 244 static const struct virtio_device_id id_table[] = { 245 { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID }, 246 { 0 }, 247 }; 248 249 static struct virtio_driver virtio_rng_driver = { 250 .driver.name = KBUILD_MODNAME, 251 .driver.owner = THIS_MODULE, 252 .id_table = id_table, 253 .probe = virtrng_probe, 254 .remove = virtrng_remove, 255 .scan = virtrng_scan, 256 #ifdef CONFIG_PM_SLEEP 257 .freeze = virtrng_freeze, 258 .restore = virtrng_restore, 259 #endif 260 }; 261 262 module_virtio_driver(virtio_rng_driver); 263 MODULE_DEVICE_TABLE(virtio, id_table); 264 MODULE_DESCRIPTION("Virtio random number driver"); 265 MODULE_LICENSE("GPL"); 266