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 "hw/qdev.h"
  14 #include "qapi/qmp/qerror.h"
  15 #include "hw/virtio.h"
  16 #include "hw/virtio-rng.h"
  17 #include "qemu/rng.h"
  18
  19 typedef struct VirtIORNG {
  20     VirtIODevice vdev;
  21
  22     DeviceState *qdev;
  23
  24     /* Only one vq - guest puts buffer(s) on it when it needs entropy */
  25     VirtQueue *vq;
  26
  27     VirtIORNGConf *conf;
  28
  29     RngBackend *rng;
  30
  31     /* We purposefully don't migrate this state.  The quota will reset on the
  32      * destination as a result.  Rate limiting is host state, not guest state.
  33      */
  34     QEMUTimer *rate_limit_timer;
  35     int64_t quota_remaining;
  36 } VirtIORNG;
  37
  38 static bool is_guest_ready(VirtIORNG *vrng)
  39 {
  40     if (virtio_queue_ready(vrng->vq)
  41         && (vrng->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK)) {
  42         return true;
  43     }
  44     return false;
  45 }
  46
  47 static size_t get_request_size(VirtQueue *vq, unsigned quota)
  48 {
  49     unsigned int in, out;
  50
  51     virtqueue_get_avail_bytes(vq, &in, &out, quota, 0);
  52     return in;
  53 }
  54
  55 static void virtio_rng_process(VirtIORNG *vrng);
  56
  57 /* Send data from a char device over to the guest */
  58 static void chr_read(void *opaque, const void *buf, size_t size)
  59 {
  60     VirtIORNG *vrng = opaque;
  61     VirtQueueElement elem;
  62     size_t len;
  63     int offset;
  64
  65     if (!is_guest_ready(vrng)) {
  66         return;
  67     }
  68
  69     vrng->quota_remaining -= size;
  70
  71     offset = 0;
  72     while (offset < size) {
  73         if (!virtqueue_pop(vrng->vq, &elem)) {
  74             break;
  75         }
  76         len = iov_from_buf(elem.in_sg, elem.in_num,
  77                            0, buf + offset, size - offset);
  78         offset += len;
  79
  80         virtqueue_push(vrng->vq, &elem, len);
  81     }
  82     virtio_notify(&vrng->vdev, vrng->vq);
  83 }
  84
  85 static void virtio_rng_process(VirtIORNG *vrng)
  86 {
  87     size_t size;
  88     unsigned quota;
  89
  90     if (!is_guest_ready(vrng)) {
  91         return;
  92     }
  93
  94     if (vrng->quota_remaining < 0) {
  95         quota = 0;
  96     } else {
  97         quota = MIN((uint64_t)vrng->quota_remaining, (uint64_t)UINT32_MAX);
  98     }
  99     size = get_request_size(vrng->vq, quota);
 100     size = MIN(vrng->quota_remaining, size);
 101     if (size) {
 102         rng_backend_request_entropy(vrng->rng, size, chr_read, vrng);
 103     }
 104 }
 105
 106 static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
 107 {
 108     VirtIORNG *vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 109     virtio_rng_process(vrng);
 110 }
 111
 112 static uint32_t get_features(VirtIODevice *vdev, uint32_t f)
 113 {
 114     return f;
 115 }
 116
 117 static void virtio_rng_save(QEMUFile *f, void *opaque)
 118 {
 119     VirtIORNG *vrng = opaque;
 120
 121     virtio_save(&vrng->vdev, f);
 122 }
 123
 124 static int virtio_rng_load(QEMUFile *f, void *opaque, int version_id)
 125 {
 126     VirtIORNG *vrng = opaque;
 127
 128     if (version_id != 1) {
 129         return -EINVAL;
 130     }
 131     virtio_load(&vrng->vdev, f);
 132
 133     /* We may have an element ready but couldn't process it due to a quota
 134      * limit.  Make sure to try again after live migration when the quota may
 135      * have been reset.
 136      */
 137     virtio_rng_process(vrng);
 138
 139     return 0;
 140 }
 141
 142 static void check_rate_limit(void *opaque)
 143 {
 144     VirtIORNG *s = opaque;
 145
 146     s->quota_remaining = s->conf->max_bytes;
 147     virtio_rng_process(s);
 148     qemu_mod_timer(s->rate_limit_timer,
 149                    qemu_get_clock_ms(vm_clock) + s->conf->period_ms);
 150 }
 151
 152
 153 VirtIODevice *virtio_rng_init(DeviceState *dev, VirtIORNGConf *conf)
 154 {
 155     VirtIORNG *vrng;
 156     VirtIODevice *vdev;
 157     Error *local_err = NULL;
 158
 159     vdev = virtio_common_init("virtio-rng", VIRTIO_ID_RNG, 0,
 160                               sizeof(VirtIORNG));
 161
 162     vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 163
 164     vrng->rng = conf->rng;
 165     if (vrng->rng == NULL) {
 166         qerror_report(QERR_INVALID_PARAMETER_VALUE, "rng", "a valid object");
 167         return NULL;
 168     }
 169
 170     rng_backend_open(vrng->rng, &local_err);
 171     if (local_err) {
 172         qerror_report_err(local_err);
 173         error_free(local_err);
 174         return NULL;
 175     }
 176
 177     vrng->vq = virtio_add_queue(vdev, 8, handle_input);
 178     vrng->vdev.get_features = get_features;
 179
 180     vrng->qdev = dev;
 181     vrng->conf = conf;
 182
 183     assert(vrng->conf->max_bytes <= INT64_MAX);
 184     vrng->quota_remaining = vrng->conf->max_bytes;
 185
 186     vrng->rate_limit_timer = qemu_new_timer_ms(vm_clock,
 187                                                check_rate_limit, vrng);
 188
 189     qemu_mod_timer(vrng->rate_limit_timer,
 190                    qemu_get_clock_ms(vm_clock) + vrng->conf->period_ms);
 191
 192     register_savevm(dev, "virtio-rng", -1, 1, virtio_rng_save,
 193                     virtio_rng_load, vrng);
 194
 195     return vdev;
 196 }
 197
 198 void virtio_rng_exit(VirtIODevice *vdev)
 199 {
 200     VirtIORNG *vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 201
 202     qemu_del_timer(vrng->rate_limit_timer);
 203     qemu_free_timer(vrng->rate_limit_timer);
 204     unregister_savevm(vrng->qdev, "virtio-rng", vrng);
 205     virtio_cleanup(vdev);
 206 }