drivers/char/hw_random/virtio-rng.c

   1 /*
   2  * Randomness driver for virtio
   3  *  Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; either version 2 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with this program; if not, write to the Free Software
  17  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  18  */
  19
  20 #include <linux/err.h>
  21 #include <linux/hw_random.h>
  22 #include <linux/scatterlist.h>
  23 #include <linux/spinlock.h>
  24 #include <linux/virtio.h>
  25 #include <linux/virtio_rng.h>
  26 #include <linux/module.h>
  27
  28 static DEFINE_IDA(rng_index_ida);
  29
  30 struct virtrng_info {
  31         struct hwrng hwrng;
  32         struct virtqueue *vq;
  33         struct completion have_data;
  34         char name[25];
  35         unsigned int data_avail;
  36         int index;
  37         bool busy;
  38         bool hwrng_register_done;
  39         bool hwrng_removed;
  40 };
  41
  42
  43 static void random_recv_done(struct virtqueue *vq)
  44 {
  45         struct virtrng_info *vi = vq->vdev->priv;
  46
  47         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
  48         if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
  49                 return;
  50
  51         complete(&vi->have_data);
  52 }
  53
  54 /* The host will fill any buffer we give it with sweet, sweet randomness. */
  55 static void register_buffer(struct virtrng_info *vi, u8 *buf, size_t size)
  56 {
  57         struct scatterlist sg;
  58
  59         sg_init_one(&sg, buf, size);
  60
  61         /* There should always be room for one buffer. */
  62         virtqueue_add_inbuf(vi->vq, &sg, 1, buf, GFP_KERNEL);
  63
  64         virtqueue_kick(vi->vq);
  65 }
  66
  67 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
  68 {
  69         int ret;
  70         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  71
  72         if (vi->hwrng_removed)
  73                 return -ENODEV;
  74
  75         if (!vi->busy) {
  76                 vi->busy = true;
  77                 init_completion(&vi->have_data);
  78                 register_buffer(vi, buf, size);
  79         }
  80
  81         if (!wait)
  82                 return 0;
  83
  84         ret = wait_for_completion_killable(&vi->have_data);
  85         if (ret < 0)
  86                 return ret;
  87
  88         vi->busy = false;
  89
  90         return vi->data_avail;
  91 }
  92
  93 static void virtio_cleanup(struct hwrng *rng)
  94 {
  95         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  96
  97         if (vi->busy)
  98                 wait_for_completion(&vi->have_data);
  99 }
 100
 101 static int probe_common(struct virtio_device *vdev)
 102 {
 103         int err, index;
 104         struct virtrng_info *vi = NULL;
 105
 106         vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
 107         if (!vi)
 108                 return -ENOMEM;
 109
 110         vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
 111         if (index < 0) {
 112                 err = index;
 113                 goto err_ida;
 114         }
 115         sprintf(vi->name, "virtio_rng.%d", index);
 116         init_completion(&vi->have_data);
 117
 118         vi->hwrng = (struct hwrng) {
 119                 .read = virtio_read,
 120                 .cleanup = virtio_cleanup,
 121                 .priv = (unsigned long)vi,
 122                 .name = vi->name,
 123                 .quality = 1000,
 124         };
 125         vdev->priv = vi;
 126
 127         /* We expect a single virtqueue. */
 128         vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 129         if (IS_ERR(vi->vq)) {
 130                 err = PTR_ERR(vi->vq);
 131                 goto err_find;
 132         }
 133
 134         return 0;
 135
 136 err_find:
 137         ida_simple_remove(&rng_index_ida, index);
 138 err_ida:
 139         kfree(vi);
 140         return err;
 141 }
 142
 143 static void remove_common(struct virtio_device *vdev)
 144 {
 145         struct virtrng_info *vi = vdev->priv;
 146
 147         vi->hwrng_removed = true;
 148         vi->data_avail = 0;
 149         complete(&vi->have_data);
 150         vdev->config->reset(vdev);
 151         vi->busy = false;
 152         if (vi->hwrng_register_done)
 153                 hwrng_unregister(&vi->hwrng);
 154         vdev->config->del_vqs(vdev);
 155         ida_simple_remove(&rng_index_ida, vi->index);
 156         kfree(vi);
 157 }
 158
 159 static int virtrng_probe(struct virtio_device *vdev)
 160 {
 161         return probe_common(vdev);
 162 }
 163
 164 static void virtrng_remove(struct virtio_device *vdev)
 165 {
 166         remove_common(vdev);
 167 }
 168
 169 static void virtrng_scan(struct virtio_device *vdev)
 170 {
 171         struct virtrng_info *vi = vdev->priv;
 172         int err;
 173
 174         err = hwrng_register(&vi->hwrng);
 175         if (!err)
 176                 vi->hwrng_register_done = true;
 177 }
 178
 179 #ifdef CONFIG_PM_SLEEP
 180 static int virtrng_freeze(struct virtio_device *vdev)
 181 {
 182         remove_common(vdev);
 183         return 0;
 184 }
 185
 186 static int virtrng_restore(struct virtio_device *vdev)
 187 {
 188         return probe_common(vdev);
 189 }
 190 #endif
 191
 192 static struct virtio_device_id id_table[] = {
 193         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 194         { 0 },
 195 };
 196
 197 static struct virtio_driver virtio_rng_driver = {
 198         .driver.name =  KBUILD_MODNAME,
 199         .driver.owner = THIS_MODULE,
 200         .id_table =     id_table,
 201         .probe =        virtrng_probe,
 202         .remove =       virtrng_remove,
 203         .scan =         virtrng_scan,
 204 #ifdef CONFIG_PM_SLEEP
 205         .freeze =       virtrng_freeze,
 206         .restore =      virtrng_restore,
 207 #endif
 208 };
 209
 210 module_virtio_driver(virtio_rng_driver);
 211 MODULE_DEVICE_TABLE(virtio, id_table);
 212 MODULE_DESCRIPTION("Virtio random number driver");
 213 MODULE_LICENSE("GPL");