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 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->hwrng_removed)
  72                 return -ENODEV;
  73
  74         if (!vi->busy) {
  75                 vi->busy = true;
  76                 init_completion(&vi->have_data);
  77                 register_buffer(vi, buf, size);
  78         }
  79
  80         if (!wait)
  81                 return 0;
  82
  83         ret = wait_for_completion_killable(&vi->have_data);
  84         if (ret < 0)
  85                 return ret;
  86
  87         vi->busy = false;
  88
  89         return vi->data_avail;
  90 }
  91
  92 static void virtio_cleanup(struct hwrng *rng)
  93 {
  94         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  95
  96         if (vi->busy)
  97                 wait_for_completion(&vi->have_data);
  98 }
  99
 100 static int probe_common(struct virtio_device *vdev)
 101 {
 102         int err, index;
 103         struct virtrng_info *vi = NULL;
 104
 105         vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
 106         if (!vi)
 107                 return -ENOMEM;
 108
 109         vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
 110         if (index < 0) {
 111                 err = index;
 112                 goto err_ida;
 113         }
 114         sprintf(vi->name, "virtio_rng.%d", index);
 115         init_completion(&vi->have_data);
 116
 117         vi->hwrng = (struct hwrng) {
 118                 .read = virtio_read,
 119                 .cleanup = virtio_cleanup,
 120                 .priv = (unsigned long)vi,
 121                 .name = vi->name,
 122                 .quality = 1000,
 123         };
 124         vdev->priv = vi;
 125
 126         /* We expect a single virtqueue. */
 127         vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 128         if (IS_ERR(vi->vq)) {
 129                 err = PTR_ERR(vi->vq);
 130                 goto err_find;
 131         }
 132
 133         return 0;
 134
 135 err_find:
 136         ida_simple_remove(&rng_index_ida, index);
 137 err_ida:
 138         kfree(vi);
 139         return err;
 140 }
 141
 142 static void remove_common(struct virtio_device *vdev)
 143 {
 144         struct virtrng_info *vi = vdev->priv;
 145
 146         vi->hwrng_removed = true;
 147         vi->data_avail = 0;
 148         complete(&vi->have_data);
 149         vdev->config->reset(vdev);
 150         vi->busy = false;
 151         if (vi->hwrng_register_done)
 152                 hwrng_unregister(&vi->hwrng);
 153         vdev->config->del_vqs(vdev);
 154         ida_simple_remove(&rng_index_ida, vi->index);
 155         kfree(vi);
 156 }
 157
 158 static int virtrng_probe(struct virtio_device *vdev)
 159 {
 160         return probe_common(vdev);
 161 }
 162
 163 static void virtrng_remove(struct virtio_device *vdev)
 164 {
 165         remove_common(vdev);
 166 }
 167
 168 static void virtrng_scan(struct virtio_device *vdev)
 169 {
 170         struct virtrng_info *vi = vdev->priv;
 171         int err;
 172
 173         err = hwrng_register(&vi->hwrng);
 174         if (!err)
 175                 vi->hwrng_register_done = true;
 176 }
 177
 178 #ifdef CONFIG_PM_SLEEP
 179 static int virtrng_freeze(struct virtio_device *vdev)
 180 {
 181         remove_common(vdev);
 182         return 0;
 183 }
 184
 185 static int virtrng_restore(struct virtio_device *vdev)
 186 {
 187         int err;
 188
 189         err = probe_common(vdev);
 190         if (!err) {
 191                 struct virtrng_info *vi = vdev->priv;
 192
 193                 /*
 194                  * Set hwrng_removed to ensure that virtio_read()
 195                  * does not block waiting for data before the
 196                  * registration is complete.
 197                  */
 198                 vi->hwrng_removed = true;
 199                 err = hwrng_register(&vi->hwrng);
 200                 if (!err) {
 201                         vi->hwrng_register_done = true;
 202                         vi->hwrng_removed = false;
 203                 }
 204         }
 205
 206         return err;
 207 }
 208 #endif
 209
 210 static struct virtio_device_id id_table[] = {
 211         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 212         { 0 },
 213 };
 214
 215 static struct virtio_driver virtio_rng_driver = {
 216         .driver.name =  KBUILD_MODNAME,
 217         .driver.owner = THIS_MODULE,
 218         .id_table =     id_table,
 219         .probe =        virtrng_probe,
 220         .remove =       virtrng_remove,
 221         .scan =         virtrng_scan,
 222 #ifdef CONFIG_PM_SLEEP
 223         .freeze =       virtrng_freeze,
 224         .restore =      virtrng_restore,
 225 #endif
 226 };
 227
 228 module_virtio_driver(virtio_rng_driver);
 229 MODULE_DEVICE_TABLE(virtio, id_table);
 230 MODULE_DESCRIPTION("Virtio random number driver");
 231 MODULE_LICENSE("GPL");