hw/virtio-rng.c

   1 /*
   2  * A virtio device implementing a hardware random number generator.
   3  *
   4  * Copyright 2012 Red Hat, Inc.
   5  * Copyright 2012 Amit Shah <amit.shah@redhat.com>
   6  *
   7  * This work is licensed under the terms of the GNU GPL, version 2 or
   8  * (at your option) any later version.  See the COPYING file in the
   9  * top-level directory.
  10  */
  11
  12 #include "qemu/iov.h"
  13 #include "qdev.h"
  14 #include "virtio.h"
  15 #include "virtio-rng.h"
  16 #include "qemu/rng.h"
  17
  18 typedef struct VirtIORNG {
  19     VirtIODevice vdev;
  20
  21     DeviceState *qdev;
  22
  23     /* Only one vq - guest puts buffer(s) on it when it needs entropy */
  24     VirtQueue *vq;
  25
  26     VirtIORNGConf *conf;
  27
  28     RngBackend *rng;
  29
  30     /* We purposefully don't migrate this state.  The quota will reset on the
  31      * destination as a result.  Rate limiting is host state, not guest state.
  32      */
  33     QEMUTimer *rate_limit_timer;
  34     int64_t quota_remaining;
  35 } VirtIORNG;
  36
  37 static bool is_guest_ready(VirtIORNG *vrng)
  38 {
  39     if (virtio_queue_ready(vrng->vq)
  40         && (vrng->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK)) {
  41         return true;
  42     }
  43     return false;
  44 }
  45
  46 static size_t get_request_size(VirtQueue *vq, unsigned quota)
  47 {
  48     unsigned int in, out;
  49
  50     virtqueue_get_avail_bytes(vq, &in, &out, quota, 0);
  51     return in;
  52 }
  53
  54 static void virtio_rng_process(VirtIORNG *vrng);
  55
  56 /* Send data from a char device over to the guest */
  57 static void chr_read(void *opaque, const void *buf, size_t size)
  58 {
  59     VirtIORNG *vrng = opaque;
  60     VirtQueueElement elem;
  61     size_t len;
  62     int offset;
  63
  64     if (!is_guest_ready(vrng)) {
  65         return;
  66     }
  67
  68     vrng->quota_remaining -= size;
  69
  70     offset = 0;
  71     while (offset < size) {
  72         if (!virtqueue_pop(vrng->vq, &elem)) {
  73             break;
  74         }
  75         len = iov_from_buf(elem.in_sg, elem.in_num,
  76                            0, buf + offset, size - offset);
  77         offset += len;
  78
  79         virtqueue_push(vrng->vq, &elem, len);
  80     }
  81     virtio_notify(&vrng->vdev, vrng->vq);
  82 }
  83
  84 static void virtio_rng_process(VirtIORNG *vrng)
  85 {
  86     size_t size;
  87     unsigned quota;
  88
  89     if (!is_guest_ready(vrng)) {
  90         return;
  91     }
  92
  93     if (vrng->quota_remaining < 0) {
  94         quota = 0;
  95     } else {
  96         quota = MIN((uint64_t)vrng->quota_remaining, (uint64_t)UINT32_MAX);
  97     }
  98     size = get_request_size(vrng->vq, quota);
  99     size = MIN(vrng->quota_remaining, size);
 100     if (size) {
 101         rng_backend_request_entropy(vrng->rng, size, chr_read, vrng);
 102     }
 103 }
 104
 105 static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
 106 {
 107     VirtIORNG *vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 108     virtio_rng_process(vrng);
 109 }
 110
 111 static uint32_t get_features(VirtIODevice *vdev, uint32_t f)
 112 {
 113     return f;
 114 }
 115
 116 static void virtio_rng_save(QEMUFile *f, void *opaque)
 117 {
 118     VirtIORNG *vrng = opaque;
 119
 120     virtio_save(&vrng->vdev, f);
 121 }
 122
 123 static int virtio_rng_load(QEMUFile *f, void *opaque, int version_id)
 124 {
 125     VirtIORNG *vrng = opaque;
 126
 127     if (version_id != 1) {
 128         return -EINVAL;
 129     }
 130     virtio_load(&vrng->vdev, f);
 131
 132     /* We may have an element ready but couldn't process it due to a quota
 133      * limit.  Make sure to try again after live migration when the quota may
 134      * have been reset.
 135      */
 136     virtio_rng_process(vrng);
 137
 138     return 0;
 139 }
 140
 141 static void check_rate_limit(void *opaque)
 142 {
 143     VirtIORNG *s = opaque;
 144
 145     s->quota_remaining = s->conf->max_bytes;
 146     virtio_rng_process(s);
 147     qemu_mod_timer(s->rate_limit_timer,
 148                    qemu_get_clock_ms(vm_clock) + s->conf->period_ms);
 149 }
 150
 151
 152 VirtIODevice *virtio_rng_init(DeviceState *dev, VirtIORNGConf *conf)
 153 {
 154     VirtIORNG *vrng;
 155     VirtIODevice *vdev;
 156     Error *local_err = NULL;
 157
 158     vdev = virtio_common_init("virtio-rng", VIRTIO_ID_RNG, 0,
 159                               sizeof(VirtIORNG));
 160
 161     vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 162
 163     vrng->rng = conf->rng;
 164     if (vrng->rng == NULL) {
 165         qerror_report(QERR_INVALID_PARAMETER_VALUE, "rng", "a valid object");
 166         return NULL;
 167     }
 168
 169     rng_backend_open(vrng->rng, &local_err);
 170     if (local_err) {
 171         qerror_report_err(local_err);
 172         error_free(local_err);
 173         return NULL;
 174     }
 175
 176     vrng->vq = virtio_add_queue(vdev, 8, handle_input);
 177     vrng->vdev.get_features = get_features;
 178
 179     vrng->qdev = dev;
 180     vrng->conf = conf;
 181
 182     assert(vrng->conf->max_bytes <= INT64_MAX);
 183     vrng->quota_remaining = vrng->conf->max_bytes;
 184
 185     vrng->rate_limit_timer = qemu_new_timer_ms(vm_clock,
 186                                                check_rate_limit, vrng);
 187
 188     qemu_mod_timer(vrng->rate_limit_timer,
 189                    qemu_get_clock_ms(vm_clock) + vrng->conf->period_ms);
 190
 191     register_savevm(dev, "virtio-rng", -1, 1, virtio_rng_save,
 192                     virtio_rng_load, vrng);
 193
 194     return vdev;
 195 }
 196
 197 void virtio_rng_exit(VirtIODevice *vdev)
 198 {
 199     VirtIORNG *vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 200
 201     qemu_del_timer(vrng->rate_limit_timer);
 202     qemu_free_timer(vrng->rate_limit_timer);
 203     unregister_savevm(vrng->qdev, "virtio-rng", vrng);
 204     virtio_cleanup(vdev);
 205 }