drivers/char/hw_random/virtio-rng.c

   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_alloc(&rng_index_ida, 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_free(&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_free(&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 static int virtrng_freeze(struct virtio_device *vdev)
 212 {
 213         remove_common(vdev);
 214         return 0;
 215 }
 216
 217 static int virtrng_restore(struct virtio_device *vdev)
 218 {
 219         int err;
 220
 221         err = probe_common(vdev);
 222         if (!err) {
 223                 struct virtrng_info *vi = vdev->priv;
 224
 225                 /*
 226                  * Set hwrng_removed to ensure that virtio_read()
 227                  * does not block waiting for data before the
 228                  * registration is complete.
 229                  */
 230                 vi->hwrng_removed = true;
 231                 err = hwrng_register(&vi->hwrng);
 232                 if (!err) {
 233                         vi->hwrng_register_done = true;
 234                         vi->hwrng_removed = false;
 235                 }
 236         }
 237
 238         return err;
 239 }
 240
 241 static const struct virtio_device_id id_table[] = {
 242         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 243         { 0 },
 244 };
 245
 246 static struct virtio_driver virtio_rng_driver = {
 247         .driver.name =  KBUILD_MODNAME,
 248         .id_table =     id_table,
 249         .probe =        virtrng_probe,
 250         .remove =       virtrng_remove,
 251         .scan =         virtrng_scan,
 252         .freeze =       pm_sleep_ptr(virtrng_freeze),
 253         .restore =      pm_sleep_ptr(virtrng_restore),
 254 };
 255
 256 module_virtio_driver(virtio_rng_driver);
 257 MODULE_DEVICE_TABLE(virtio, id_table);
 258 MODULE_DESCRIPTION("Virtio random number driver");
 259 MODULE_LICENSE("GPL");