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 <asm/barrier.h> 8 #include <linux/err.h> 9 #include <linux/hw_random.h> 10 #include <linux/scatterlist.h> 11 #include <linux/spinlock.h> 12 #include <linux/virtio.h> 13 #include <linux/virtio_rng.h> 14 #include <linux/module.h> 15 #include <linux/slab.h> 16 17 static DEFINE_IDA(rng_index_ida); 18 19 struct virtrng_info { 20 struct hwrng hwrng; 21 struct virtqueue *vq; 22 char name[25]; 23 int index; 24 bool hwrng_register_done; 25 bool hwrng_removed; 26 /* data transfer */ 27 struct completion have_data; 28 unsigned int data_avail; 29 unsigned int data_idx; 30 /* minimal size returned by rng_buffer_size() */ 31 #if SMP_CACHE_BYTES < 32 32 u8 data[32]; 33 #else 34 u8 data[SMP_CACHE_BYTES]; 35 #endif 36 }; 37 38 static void random_recv_done(struct virtqueue *vq) 39 { 40 struct virtrng_info *vi = vq->vdev->priv; 41 unsigned int len; 42 43 /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */ 44 if (!virtqueue_get_buf(vi->vq, &len)) 45 return; 46 47 smp_store_release(&vi->data_avail, len); 48 complete(&vi->have_data); 49 } 50 51 static void request_entropy(struct virtrng_info *vi) 52 { 53 struct scatterlist sg; 54 55 reinit_completion(&vi->have_data); 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 (smp_load_acquire(&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 }; 152 vdev->priv = vi; 153 154 /* We expect a single virtqueue. */ 155 vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input"); 156 if (IS_ERR(vi->vq)) { 157 err = PTR_ERR(vi->vq); 158 goto err_find; 159 } 160 161 virtio_device_ready(vdev); 162 163 /* we always have a pending entropy request */ 164 request_entropy(vi); 165 166 return 0; 167 168 err_find: 169 ida_simple_remove(&rng_index_ida, index); 170 err_ida: 171 kfree(vi); 172 return err; 173 } 174 175 static void remove_common(struct virtio_device *vdev) 176 { 177 struct virtrng_info *vi = vdev->priv; 178 179 vi->hwrng_removed = true; 180 vi->data_avail = 0; 181 vi->data_idx = 0; 182 complete(&vi->have_data); 183 if (vi->hwrng_register_done) 184 hwrng_unregister(&vi->hwrng); 185 virtio_reset_device(vdev); 186 vdev->config->del_vqs(vdev); 187 ida_simple_remove(&rng_index_ida, vi->index); 188 kfree(vi); 189 } 190 191 static int virtrng_probe(struct virtio_device *vdev) 192 { 193 return probe_common(vdev); 194 } 195 196 static void virtrng_remove(struct virtio_device *vdev) 197 { 198 remove_common(vdev); 199 } 200 201 static void virtrng_scan(struct virtio_device *vdev) 202 { 203 struct virtrng_info *vi = vdev->priv; 204 int err; 205 206 err = hwrng_register(&vi->hwrng); 207 if (!err) 208 vi->hwrng_register_done = true; 209 } 210 211 #ifdef CONFIG_PM_SLEEP 212 static int virtrng_freeze(struct virtio_device *vdev) 213 { 214 remove_common(vdev); 215 return 0; 216 } 217 218 static int virtrng_restore(struct virtio_device *vdev) 219 { 220 int err; 221 222 err = probe_common(vdev); 223 if (!err) { 224 struct virtrng_info *vi = vdev->priv; 225 226 /* 227 * Set hwrng_removed to ensure that virtio_read() 228 * does not block waiting for data before the 229 * registration is complete. 230 */ 231 vi->hwrng_removed = true; 232 err = hwrng_register(&vi->hwrng); 233 if (!err) { 234 vi->hwrng_register_done = true; 235 vi->hwrng_removed = false; 236 } 237 } 238 239 return err; 240 } 241 #endif 242 243 static const struct virtio_device_id id_table[] = { 244 { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID }, 245 { 0 }, 246 }; 247 248 static struct virtio_driver virtio_rng_driver = { 249 .driver.name = KBUILD_MODNAME, 250 .driver.owner = THIS_MODULE, 251 .id_table = id_table, 252 .probe = virtrng_probe, 253 .remove = virtrng_remove, 254 .scan = virtrng_scan, 255 #ifdef CONFIG_PM_SLEEP 256 .freeze = virtrng_freeze, 257 .restore = virtrng_restore, 258 #endif 259 }; 260 261 module_virtio_driver(virtio_rng_driver); 262 MODULE_DEVICE_TABLE(virtio, id_table); 263 MODULE_DESCRIPTION("Virtio random number driver"); 264 MODULE_LICENSE("GPL"); 265