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 virtio_device *vdev;
  32         struct hwrng hwrng;
  33         struct virtqueue *vq;
  34         unsigned int data_avail;
  35         struct completion have_data;
  36         bool busy;
  37         char name[25];
  38         int index;
  39 };
  40
  41 static void random_recv_done(struct virtqueue *vq)
  42 {
  43         struct virtrng_info *vi = vq->vdev->priv;
  44
  45         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
  46         if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
  47                 return;
  48
  49         complete(&vi->have_data);
  50 }
  51
  52 /* The host will fill any buffer we give it with sweet, sweet randomness. */
  53 static void register_buffer(struct virtrng_info *vi, u8 *buf, size_t size)
  54 {
  55         struct scatterlist sg;
  56
  57         sg_init_one(&sg, buf, size);
  58
  59         /* There should always be room for one buffer. */
  60         virtqueue_add_inbuf(vi->vq, &sg, 1, buf, GFP_KERNEL);
  61
  62         virtqueue_kick(vi->vq);
  63 }
  64
  65 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
  66 {
  67         int ret;
  68         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  69
  70         if (!vi->busy) {
  71                 vi->busy = true;
  72                 init_completion(&vi->have_data);
  73                 register_buffer(vi, buf, size);
  74         }
  75
  76         if (!wait)
  77                 return 0;
  78
  79         ret = wait_for_completion_killable(&vi->have_data);
  80         if (ret < 0)
  81                 return ret;
  82
  83         vi->busy = false;
  84
  85         return vi->data_avail;
  86 }
  87
  88 static void virtio_cleanup(struct hwrng *rng)
  89 {
  90         struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
  91
  92         if (vi->busy)
  93                 wait_for_completion(&vi->have_data);
  94 }
  95
  96 static int probe_common(struct virtio_device *vdev)
  97 {
  98         int err, index;
  99         struct virtrng_info *vi = NULL;
 100
 101         vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
 102         if (!vi)
 103                 return -ENOMEM;
 104
 105         vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
 106         if (index < 0) {
 107                 kfree(vi);
 108                 return index;
 109         }
 110         sprintf(vi->name, "virtio_rng.%d", index);
 111         init_completion(&vi->have_data);
 112
 113         vi->hwrng = (struct hwrng) {
 114                 .read = virtio_read,
 115                 .cleanup = virtio_cleanup,
 116                 .priv = (unsigned long)vi,
 117                 .name = vi->name,
 118         };
 119         vdev->priv = vi;
 120
 121         /* We expect a single virtqueue. */
 122         vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 123         if (IS_ERR(vi->vq)) {
 124                 err = PTR_ERR(vi->vq);
 125                 vi->vq = NULL;
 126                 kfree(vi);
 127                 ida_simple_remove(&rng_index_ida, index);
 128                 return err;
 129         }
 130
 131         err = hwrng_register(&vi->hwrng);
 132         if (err) {
 133                 vdev->config->del_vqs(vdev);
 134                 vi->vq = NULL;
 135                 kfree(vi);
 136                 ida_simple_remove(&rng_index_ida, index);
 137                 return err;
 138         }
 139
 140         return 0;
 141 }
 142
 143 static void remove_common(struct virtio_device *vdev)
 144 {
 145         struct virtrng_info *vi = vdev->priv;
 146         vdev->config->reset(vdev);
 147         vi->busy = false;
 148         hwrng_unregister(&vi->hwrng);
 149         vdev->config->del_vqs(vdev);
 150         ida_simple_remove(&rng_index_ida, vi->index);
 151         kfree(vi);
 152 }
 153
 154 static int virtrng_probe(struct virtio_device *vdev)
 155 {
 156         return probe_common(vdev);
 157 }
 158
 159 static void virtrng_remove(struct virtio_device *vdev)
 160 {
 161         remove_common(vdev);
 162 }
 163
 164 #ifdef CONFIG_PM_SLEEP
 165 static int virtrng_freeze(struct virtio_device *vdev)
 166 {
 167         remove_common(vdev);
 168         return 0;
 169 }
 170
 171 static int virtrng_restore(struct virtio_device *vdev)
 172 {
 173         return probe_common(vdev);
 174 }
 175 #endif
 176
 177 static struct virtio_device_id id_table[] = {
 178         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 179         { 0 },
 180 };
 181
 182 static struct virtio_driver virtio_rng_driver = {
 183         .driver.name =  KBUILD_MODNAME,
 184         .driver.owner = THIS_MODULE,
 185         .id_table =     id_table,
 186         .probe =        virtrng_probe,
 187         .remove =       virtrng_remove,
 188 #ifdef CONFIG_PM_SLEEP
 189         .freeze =       virtrng_freeze,
 190         .restore =      virtrng_restore,
 191 #endif
 192 };
 193
 194 module_virtio_driver(virtio_rng_driver);
 195 MODULE_DEVICE_TABLE(virtio, id_table);
 196 MODULE_DESCRIPTION("Virtio random number driver");
 197 MODULE_LICENSE("GPL");