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 };
  40
  41
  42 static void random_recv_done(struct virtqueue *vq)
  43 {
  44         struct virtrng_info *vi = vq->vdev->priv;
  45
  46         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
  47         if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
  48                 return;
  49
  50         complete(&vi->have_data);
  51 }
  52
  53 /* The host will fill any buffer we give it with sweet, sweet randomness. */
  54 static void register_buffer(struct virtrng_info *vi, u8 *buf, size_t size)
  55 {
  56         struct scatterlist sg;
  57
  58         sg_init_one(&sg, buf, size);
  59
  60         /* There should always be room for one buffer. */
  61         virtqueue_add_inbuf(vi->vq, &sg, 1, buf, GFP_KERNEL);
  62
  63         virtqueue_kick(vi->vq);
  64 }
  65
  66 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
  67 {
  68         int ret;
  69         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  70
  71         if (!vi->busy) {
  72                 vi->busy = true;
  73                 init_completion(&vi->have_data);
  74                 register_buffer(vi, buf, size);
  75         }
  76
  77         if (!wait)
  78                 return 0;
  79
  80         ret = wait_for_completion_killable(&vi->have_data);
  81         if (ret < 0)
  82                 return ret;
  83
  84         vi->busy = false;
  85
  86         return vi->data_avail;
  87 }
  88
  89 static void virtio_cleanup(struct hwrng *rng)
  90 {
  91         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  92
  93         if (vi->busy)
  94                 wait_for_completion(&vi->have_data);
  95 }
  96
  97 static int probe_common(struct virtio_device *vdev)
  98 {
  99         int err, index;
 100         struct virtrng_info *vi = NULL;
 101
 102         vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
 103         if (!vi)
 104                 return -ENOMEM;
 105
 106         vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
 107         if (index < 0) {
 108                 kfree(vi);
 109                 return index;
 110         }
 111         sprintf(vi->name, "virtio_rng.%d", index);
 112         init_completion(&vi->have_data);
 113
 114         vi->hwrng = (struct hwrng) {
 115                 .read = virtio_read,
 116                 .cleanup = virtio_cleanup,
 117                 .priv = (unsigned long)vi,
 118                 .name = vi->name,
 119                 .quality = 1000,
 120         };
 121         vdev->priv = vi;
 122
 123         /* We expect a single virtqueue. */
 124         vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 125         if (IS_ERR(vi->vq)) {
 126                 err = PTR_ERR(vi->vq);
 127                 vi->vq = NULL;
 128                 kfree(vi);
 129                 ida_simple_remove(&rng_index_ida, index);
 130                 return err;
 131         }
 132
 133         return 0;
 134 }
 135
 136 static void remove_common(struct virtio_device *vdev)
 137 {
 138         struct virtrng_info *vi = vdev->priv;
 139
 140         vi->data_avail = 0;
 141         complete(&vi->have_data);
 142         vdev->config->reset(vdev);
 143         vi->busy = false;
 144         if (vi->hwrng_register_done)
 145                 hwrng_unregister(&vi->hwrng);
 146         vdev->config->del_vqs(vdev);
 147         ida_simple_remove(&rng_index_ida, vi->index);
 148         kfree(vi);
 149 }
 150
 151 static int virtrng_probe(struct virtio_device *vdev)
 152 {
 153         return probe_common(vdev);
 154 }
 155
 156 static void virtrng_remove(struct virtio_device *vdev)
 157 {
 158         remove_common(vdev);
 159 }
 160
 161 static void virtrng_scan(struct virtio_device *vdev)
 162 {
 163         struct virtrng_info *vi = vdev->priv;
 164         int err;
 165
 166         err = hwrng_register(&vi->hwrng);
 167         if (!err)
 168                 vi->hwrng_register_done = true;
 169 }
 170
 171 #ifdef CONFIG_PM_SLEEP
 172 static int virtrng_freeze(struct virtio_device *vdev)
 173 {
 174         remove_common(vdev);
 175         return 0;
 176 }
 177
 178 static int virtrng_restore(struct virtio_device *vdev)
 179 {
 180         return probe_common(vdev);
 181 }
 182 #endif
 183
 184 static struct virtio_device_id id_table[] = {
 185         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 186         { 0 },
 187 };
 188
 189 static struct virtio_driver virtio_rng_driver = {
 190         .driver.name =  KBUILD_MODNAME,
 191         .driver.owner = THIS_MODULE,
 192         .id_table =     id_table,
 193         .probe =        virtrng_probe,
 194         .remove =       virtrng_remove,
 195         .scan =         virtrng_scan,
 196 #ifdef CONFIG_PM_SLEEP
 197         .freeze =       virtrng_freeze,
 198         .restore =      virtrng_restore,
 199 #endif
 200 };
 201
 202 module_virtio_driver(virtio_rng_driver);
 203 MODULE_DEVICE_TABLE(virtio, id_table);
 204 MODULE_DESCRIPTION("Virtio random number driver");
 205 MODULE_LICENSE("GPL");