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 <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         struct completion have_data;
  22         char name[25];
  23         unsigned int data_avail;
  24         int index;
  25         bool busy;
  26         bool hwrng_register_done;
  27         bool hwrng_removed;
  28 };
  29
  30 static void random_recv_done(struct virtqueue *vq)
  31 {
  32         struct virtrng_info *vi = vq->vdev->priv;
  33
  34         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
  35         if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
  36                 return;
  37
  38         complete(&vi->have_data);
  39 }
  40
  41 /* The host will fill any buffer we give it with sweet, sweet randomness. */
  42 static void register_buffer(struct virtrng_info *vi, u8 *buf, size_t size)
  43 {
  44         struct scatterlist sg;
  45
  46         sg_init_one(&sg, buf, size);
  47
  48         /* There should always be room for one buffer. */
  49         virtqueue_add_inbuf(vi->vq, &sg, 1, buf, GFP_KERNEL);
  50
  51         virtqueue_kick(vi->vq);
  52 }
  53
  54 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
  55 {
  56         int ret;
  57         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  58
  59         if (vi->hwrng_removed)
  60                 return -ENODEV;
  61
  62         if (!vi->busy) {
  63                 vi->busy = true;
  64                 reinit_completion(&vi->have_data);
  65                 register_buffer(vi, buf, size);
  66         }
  67
  68         if (!wait)
  69                 return 0;
  70
  71         ret = wait_for_completion_killable(&vi->have_data);
  72         if (ret < 0)
  73                 return ret;
  74
  75         vi->busy = false;
  76
  77         return vi->data_avail;
  78 }
  79
  80 static void virtio_cleanup(struct hwrng *rng)
  81 {
  82         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  83
  84         if (vi->busy)
  85                 wait_for_completion(&vi->have_data);
  86 }
  87
  88 static int probe_common(struct virtio_device *vdev)
  89 {
  90         int err, index;
  91         struct virtrng_info *vi = NULL;
  92
  93         vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
  94         if (!vi)
  95                 return -ENOMEM;
  96
  97         vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
  98         if (index < 0) {
  99                 err = index;
 100                 goto err_ida;
 101         }
 102         sprintf(vi->name, "virtio_rng.%d", index);
 103         init_completion(&vi->have_data);
 104
 105         vi->hwrng = (struct hwrng) {
 106                 .read = virtio_read,
 107                 .cleanup = virtio_cleanup,
 108                 .priv = (unsigned long)vi,
 109                 .name = vi->name,
 110                 .quality = 1000,
 111         };
 112         vdev->priv = vi;
 113
 114         /* We expect a single virtqueue. */
 115         vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 116         if (IS_ERR(vi->vq)) {
 117                 err = PTR_ERR(vi->vq);
 118                 goto err_find;
 119         }
 120
 121         return 0;
 122
 123 err_find:
 124         ida_simple_remove(&rng_index_ida, index);
 125 err_ida:
 126         kfree(vi);
 127         return err;
 128 }
 129
 130 static void remove_common(struct virtio_device *vdev)
 131 {
 132         struct virtrng_info *vi = vdev->priv;
 133
 134         vi->hwrng_removed = true;
 135         vi->data_avail = 0;
 136         complete(&vi->have_data);
 137         vdev->config->reset(vdev);
 138         vi->busy = false;
 139         if (vi->hwrng_register_done)
 140                 hwrng_unregister(&vi->hwrng);
 141         vdev->config->del_vqs(vdev);
 142         ida_simple_remove(&rng_index_ida, vi->index);
 143         kfree(vi);
 144 }
 145
 146 static int virtrng_probe(struct virtio_device *vdev)
 147 {
 148         return probe_common(vdev);
 149 }
 150
 151 static void virtrng_remove(struct virtio_device *vdev)
 152 {
 153         remove_common(vdev);
 154 }
 155
 156 static void virtrng_scan(struct virtio_device *vdev)
 157 {
 158         struct virtrng_info *vi = vdev->priv;
 159         int err;
 160
 161         err = hwrng_register(&vi->hwrng);
 162         if (!err)
 163                 vi->hwrng_register_done = true;
 164 }
 165
 166 #ifdef CONFIG_PM_SLEEP
 167 static int virtrng_freeze(struct virtio_device *vdev)
 168 {
 169         remove_common(vdev);
 170         return 0;
 171 }
 172
 173 static int virtrng_restore(struct virtio_device *vdev)
 174 {
 175         int err;
 176
 177         err = probe_common(vdev);
 178         if (!err) {
 179                 struct virtrng_info *vi = vdev->priv;
 180
 181                 /*
 182                  * Set hwrng_removed to ensure that virtio_read()
 183                  * does not block waiting for data before the
 184                  * registration is complete.
 185                  */
 186                 vi->hwrng_removed = true;
 187                 err = hwrng_register(&vi->hwrng);
 188                 if (!err) {
 189                         vi->hwrng_register_done = true;
 190                         vi->hwrng_removed = false;
 191                 }
 192         }
 193
 194         return err;
 195 }
 196 #endif
 197
 198 static struct virtio_device_id id_table[] = {
 199         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 200         { 0 },
 201 };
 202
 203 static struct virtio_driver virtio_rng_driver = {
 204         .driver.name =  KBUILD_MODNAME,
 205         .driver.owner = THIS_MODULE,
 206         .id_table =     id_table,
 207         .probe =        virtrng_probe,
 208         .remove =       virtrng_remove,
 209         .scan =         virtrng_scan,
 210 #ifdef CONFIG_PM_SLEEP
 211         .freeze =       virtrng_freeze,
 212         .restore =      virtrng_restore,
 213 #endif
 214 };
 215
 216 module_virtio_driver(virtio_rng_driver);
 217 MODULE_DEVICE_TABLE(virtio, id_table);
 218 MODULE_DESCRIPTION("Virtio random number driver");
 219 MODULE_LICENSE("GPL");