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 <[email protected]>
   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 "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     VirtQueueElement elem;
  26
  27     /* Config data for the device -- currently only chardev */
  28     VirtIORNGConf *conf;
  29
  30     /* Whether we've popped a vq element into 'elem' above */
  31     bool popped;
  32
  33     RngBackend *rng;
  34
  35     /* We purposefully don't migrate this state.  The quota will reset on the
  36      * destination as a result.  Rate limiting is host state, not guest state.
  37      */
  38     QEMUTimer *rate_limit_timer;
  39     int64_t quota_remaining;
  40 } VirtIORNG;
  41
  42 static bool is_guest_ready(VirtIORNG *vrng)
  43 {
  44     if (virtio_queue_ready(vrng->vq)
  45         && (vrng->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK)) {
  46         return true;
  47     }
  48     return false;
  49 }
  50
  51 static size_t pop_an_elem(VirtIORNG *vrng)
  52 {
  53     size_t size;
  54
  55     if (!vrng->popped && !virtqueue_pop(vrng->vq, &vrng->elem)) {
  56         return 0;
  57     }
  58     vrng->popped = true;
  59
  60     size = iov_size(vrng->elem.in_sg, vrng->elem.in_num);
  61     return size;
  62 }
  63
  64 static void virtio_rng_process(VirtIORNG *vrng);
  65
  66 /* Send data from a char device over to the guest */
  67 static void chr_read(void *opaque, const void *buf, size_t size)
  68 {
  69     VirtIORNG *vrng = opaque;
  70     size_t len;
  71     int offset;
  72
  73     if (!is_guest_ready(vrng)) {
  74         return;
  75     }
  76
  77     vrng->quota_remaining -= size;
  78
  79     offset = 0;
  80     while (offset < size) {
  81         if (!pop_an_elem(vrng)) {
  82             break;
  83         }
  84         len = iov_from_buf(vrng->elem.in_sg, vrng->elem.in_num,
  85                            0, buf + offset, size - offset);
  86         offset += len;
  87
  88         virtqueue_push(vrng->vq, &vrng->elem, len);
  89         vrng->popped = false;
  90     }
  91     virtio_notify(&vrng->vdev, vrng->vq);
  92
  93     /*
  94      * Lastly, if we had multiple elems queued by the guest, and we
  95      * didn't have enough data to fill them all, indicate we want more
  96      * data.
  97      */
  98     virtio_rng_process(vrng);
  99 }
 100
 101 static void virtio_rng_process(VirtIORNG *vrng)
 102 {
 103     ssize_t size;
 104
 105     if (!is_guest_ready(vrng)) {
 106         return;
 107     }
 108
 109     size = pop_an_elem(vrng);
 110     size = MIN(vrng->quota_remaining, size);
 111
 112     if (size > 0) {
 113         rng_backend_request_entropy(vrng->rng, size, chr_read, vrng);
 114     }
 115 }
 116
 117
 118 static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
 119 {
 120     VirtIORNG *vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 121     virtio_rng_process(vrng);
 122 }
 123
 124 static uint32_t get_features(VirtIODevice *vdev, uint32_t f)
 125 {
 126     return f;
 127 }
 128
 129 static void virtio_rng_save(QEMUFile *f, void *opaque)
 130 {
 131     VirtIORNG *vrng = opaque;
 132
 133     virtio_save(&vrng->vdev, f);
 134
 135     qemu_put_byte(f, vrng->popped);
 136     if (vrng->popped) {
 137         int i;
 138
 139         qemu_put_be32(f, vrng->elem.index);
 140
 141         qemu_put_be32(f, vrng->elem.in_num);
 142         for (i = 0; i < vrng->elem.in_num; i++) {
 143             qemu_put_be64(f, vrng->elem.in_addr[i]);
 144         }
 145
 146         qemu_put_be32(f, vrng->elem.out_num);
 147         for (i = 0; i < vrng->elem.out_num; i++) {
 148             qemu_put_be64(f, vrng->elem.out_addr[i]);
 149         }
 150     }
 151 }
 152
 153 static int virtio_rng_load(QEMUFile *f, void *opaque, int version_id)
 154 {
 155     VirtIORNG *vrng = opaque;
 156
 157     if (version_id != 1) {
 158         return -EINVAL;
 159     }
 160     virtio_load(&vrng->vdev, f);
 161
 162     vrng->popped = qemu_get_byte(f);
 163     if (vrng->popped) {
 164         int i;
 165
 166         vrng->elem.index = qemu_get_be32(f);
 167
 168         vrng->elem.in_num = qemu_get_be32(f);
 169         g_assert(vrng->elem.in_num < VIRTQUEUE_MAX_SIZE);
 170         for (i = 0; i < vrng->elem.in_num; i++) {
 171             vrng->elem.in_addr[i] = qemu_get_be64(f);
 172         }
 173
 174         vrng->elem.out_num = qemu_get_be32(f);
 175         g_assert(vrng->elem.out_num < VIRTQUEUE_MAX_SIZE);
 176         for (i = 0; i < vrng->elem.out_num; i++) {
 177             vrng->elem.out_addr[i] = qemu_get_be64(f);
 178         }
 179
 180         virtqueue_map_sg(vrng->elem.in_sg, vrng->elem.in_addr,
 181                          vrng->elem.in_num, 1);
 182         virtqueue_map_sg(vrng->elem.out_sg, vrng->elem.out_addr,
 183                          vrng->elem.out_num, 0);
 184     }
 185
 186     /* We may have an element ready but couldn't process it due to a quota
 187        limit.  Make sure to try again after live migration when the quota may
 188        have been reset.
 189     */
 190     virtio_rng_process(vrng);
 191
 192     return 0;
 193 }
 194
 195 static void check_rate_limit(void *opaque)
 196 {
 197     VirtIORNG *s = opaque;
 198
 199     s->quota_remaining = s->conf->max_bytes;
 200     virtio_rng_process(s);
 201     qemu_mod_timer(s->rate_limit_timer,
 202                    qemu_get_clock_ms(vm_clock) + s->conf->period_ms);
 203 }
 204
 205
 206 VirtIODevice *virtio_rng_init(DeviceState *dev, VirtIORNGConf *conf)
 207 {
 208     VirtIORNG *vrng;
 209     VirtIODevice *vdev;
 210     Error *local_err = NULL;
 211
 212     vdev = virtio_common_init("virtio-rng", VIRTIO_ID_RNG, 0,
 213                               sizeof(VirtIORNG));
 214
 215     vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 216
 217     vrng->rng = conf->rng;
 218     if (vrng->rng == NULL) {
 219         qerror_report(QERR_INVALID_PARAMETER_VALUE, "rng", "a valid object");
 220         return NULL;
 221     }
 222
 223     rng_backend_open(vrng->rng, &local_err);
 224     if (local_err) {
 225         qerror_report_err(local_err);
 226         error_free(local_err);
 227         return NULL;
 228     }
 229
 230     vrng->vq = virtio_add_queue(vdev, 8, handle_input);
 231     vrng->vdev.get_features = get_features;
 232
 233     vrng->qdev = dev;
 234     vrng->conf = conf;
 235     vrng->popped = false;
 236     vrng->quota_remaining = vrng->conf->max_bytes;
 237
 238     g_assert_cmpint(vrng->conf->max_bytes, <=, INT64_MAX);
 239
 240     vrng->rate_limit_timer = qemu_new_timer_ms(vm_clock,
 241                                                check_rate_limit, vrng);
 242
 243     qemu_mod_timer(vrng->rate_limit_timer,
 244                    qemu_get_clock_ms(vm_clock) + vrng->conf->period_ms);
 245
 246     register_savevm(dev, "virtio-rng", -1, 1, virtio_rng_save,
 247                     virtio_rng_load, vrng);
 248
 249     return vdev;
 250 }
 251
 252 void virtio_rng_exit(VirtIODevice *vdev)
 253 {
 254     VirtIORNG *vrng = DO_UPCAST(VirtIORNG, vdev, vdev);
 255
 256     unregister_savevm(vrng->qdev, "virtio-rng", vrng);
 257     virtio_cleanup(vdev);
 258 }