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