xref: /openbmc/qemu/hw/virtio/virtio-rng.c (revision 024d046b)
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/osdep.h"
13 #include "qapi/error.h"
14 #include "qemu/iov.h"
15 #include "qemu/module.h"
16 #include "qemu/timer.h"
17 #include "hw/virtio/virtio.h"
18 #include "hw/qdev-properties.h"
19 #include "hw/virtio/virtio-rng.h"
20 #include "sysemu/rng.h"
21 #include "sysemu/runstate.h"
22 #include "qom/object_interfaces.h"
23 #include "trace.h"
24 
is_guest_ready(VirtIORNG * vrng)25 static bool is_guest_ready(VirtIORNG *vrng)
26 {
27     VirtIODevice *vdev = VIRTIO_DEVICE(vrng);
28     if (virtio_queue_ready(vrng->vq)
29         && (vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
30         return true;
31     }
32     trace_virtio_rng_guest_not_ready(vrng);
33     return false;
34 }
35 
get_request_size(VirtQueue * vq,unsigned quota)36 static size_t get_request_size(VirtQueue *vq, unsigned quota)
37 {
38     unsigned int in, out;
39 
40     virtqueue_get_avail_bytes(vq, &in, &out, quota, 0);
41     return in;
42 }
43 
44 static void virtio_rng_process(VirtIORNG *vrng);
45 
46 /* Send data from a char device over to the guest */
chr_read(void * opaque,const void * buf,size_t size)47 static void chr_read(void *opaque, const void *buf, size_t size)
48 {
49     VirtIORNG *vrng = opaque;
50     VirtIODevice *vdev = VIRTIO_DEVICE(vrng);
51     VirtQueueElement *elem;
52     size_t len;
53     int offset;
54 
55     if (!is_guest_ready(vrng)) {
56         return;
57     }
58 
59     /* we can't modify the virtqueue until
60      * our state is fully synced
61      */
62 
63     if (!runstate_check(RUN_STATE_RUNNING)) {
64         trace_virtio_rng_cpu_is_stopped(vrng, size);
65         return;
66     }
67 
68     vrng->quota_remaining -= size;
69 
70     offset = 0;
71     while (offset < size) {
72         elem = virtqueue_pop(vrng->vq, sizeof(VirtQueueElement));
73         if (!elem) {
74             break;
75         }
76         trace_virtio_rng_popped(vrng);
77         len = iov_from_buf(elem->in_sg, elem->in_num,
78                            0, buf + offset, size - offset);
79         offset += len;
80 
81         virtqueue_push(vrng->vq, elem, len);
82         trace_virtio_rng_pushed(vrng, len);
83         g_free(elem);
84     }
85     virtio_notify(vdev, vrng->vq);
86 
87     if (!virtio_queue_empty(vrng->vq)) {
88         /* If we didn't drain the queue, call virtio_rng_process
89          * to take care of asking for more data as appropriate.
90          */
91         virtio_rng_process(vrng);
92     }
93 }
94 
virtio_rng_process(VirtIORNG * vrng)95 static void virtio_rng_process(VirtIORNG *vrng)
96 {
97     size_t size;
98     unsigned quota;
99 
100     if (!is_guest_ready(vrng)) {
101         return;
102     }
103 
104     if (vrng->activate_timer) {
105         timer_mod(vrng->rate_limit_timer,
106                   qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + vrng->conf.period_ms);
107         vrng->activate_timer = false;
108     }
109 
110     if (vrng->quota_remaining < 0) {
111         quota = 0;
112     } else {
113         quota = MIN((uint64_t)vrng->quota_remaining, (uint64_t)UINT32_MAX);
114     }
115     size = get_request_size(vrng->vq, quota);
116 
117     trace_virtio_rng_request(vrng, size, quota);
118 
119     size = MIN(vrng->quota_remaining, size);
120     if (size) {
121         rng_backend_request_entropy(vrng->rng, size, chr_read, vrng);
122     }
123 }
124 
handle_input(VirtIODevice * vdev,VirtQueue * vq)125 static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
126 {
127     VirtIORNG *vrng = VIRTIO_RNG(vdev);
128     virtio_rng_process(vrng);
129 }
130 
get_features(VirtIODevice * vdev,uint64_t f,Error ** errp)131 static uint64_t get_features(VirtIODevice *vdev, uint64_t f, Error **errp)
132 {
133     return f;
134 }
135 
virtio_rng_vm_state_change(void * opaque,bool running,RunState state)136 static void virtio_rng_vm_state_change(void *opaque, bool running,
137                                        RunState state)
138 {
139     VirtIORNG *vrng = opaque;
140 
141     trace_virtio_rng_vm_state_change(vrng, running, state);
142 
143     /* We may have an element ready but couldn't process it due to a quota
144      * limit or because CPU was stopped.  Make sure to try again when the
145      * CPU restart.
146      */
147 
148     if (running && is_guest_ready(vrng)) {
149         virtio_rng_process(vrng);
150     }
151 }
152 
check_rate_limit(void * opaque)153 static void check_rate_limit(void *opaque)
154 {
155     VirtIORNG *vrng = opaque;
156 
157     vrng->quota_remaining = vrng->conf.max_bytes;
158     virtio_rng_process(vrng);
159     vrng->activate_timer = true;
160 }
161 
virtio_rng_set_status(VirtIODevice * vdev,uint8_t status)162 static void virtio_rng_set_status(VirtIODevice *vdev, uint8_t status)
163 {
164     VirtIORNG *vrng = VIRTIO_RNG(vdev);
165 
166     if (!vdev->vm_running) {
167         return;
168     }
169     vdev->status = status;
170 
171     /* Something changed, try to process buffers */
172     virtio_rng_process(vrng);
173 }
174 
virtio_rng_device_realize(DeviceState * dev,Error ** errp)175 static void virtio_rng_device_realize(DeviceState *dev, Error **errp)
176 {
177     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
178     VirtIORNG *vrng = VIRTIO_RNG(dev);
179 
180     if (vrng->conf.period_ms <= 0) {
181         error_setg(errp, "'period' parameter expects a positive integer");
182         return;
183     }
184 
185     /* Workaround: Property parsing does not enforce unsigned integers,
186      * So this is a hack to reject such numbers. */
187     if (vrng->conf.max_bytes == 0 ||
188         vrng->conf.max_bytes > INT64_MAX) {
189         error_setg(errp, "'max-bytes' parameter must be positive, "
190                    "and less than 2^63");
191         return;
192     }
193 
194     if (vrng->conf.rng == NULL) {
195         Object *default_backend = object_new(TYPE_RNG_BUILTIN);
196 
197         if (!user_creatable_complete(USER_CREATABLE(default_backend),
198                                      errp)) {
199             object_unref(default_backend);
200             return;
201         }
202 
203         object_property_add_child(OBJECT(dev), "default-backend",
204                                   default_backend);
205 
206         /* The child property took a reference, we can safely drop ours now */
207         object_unref(default_backend);
208 
209         object_property_set_link(OBJECT(dev), "rng", default_backend,
210                                  &error_abort);
211     }
212 
213     vrng->rng = vrng->conf.rng;
214     if (vrng->rng == NULL) {
215         error_setg(errp, "'rng' parameter expects a valid object");
216         return;
217     }
218 
219     virtio_init(vdev, VIRTIO_ID_RNG, 0);
220 
221     vrng->vq = virtio_add_queue(vdev, 8, handle_input);
222     vrng->quota_remaining = vrng->conf.max_bytes;
223     vrng->rate_limit_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
224                                                check_rate_limit, vrng);
225     vrng->activate_timer = true;
226 
227     vrng->vmstate = qemu_add_vm_change_state_handler(virtio_rng_vm_state_change,
228                                                      vrng);
229 }
230 
virtio_rng_device_unrealize(DeviceState * dev)231 static void virtio_rng_device_unrealize(DeviceState *dev)
232 {
233     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
234     VirtIORNG *vrng = VIRTIO_RNG(dev);
235 
236     qemu_del_vm_change_state_handler(vrng->vmstate);
237     timer_free(vrng->rate_limit_timer);
238     virtio_del_queue(vdev, 0);
239     virtio_cleanup(vdev);
240 }
241 
242 static const VMStateDescription vmstate_virtio_rng = {
243     .name = "virtio-rng",
244     .minimum_version_id = 1,
245     .version_id = 1,
246     .fields = (const VMStateField[]) {
247         VMSTATE_VIRTIO_DEVICE,
248         VMSTATE_END_OF_LIST()
249     },
250 };
251 
252 static Property virtio_rng_properties[] = {
253     /* Set a default rate limit of 2^47 bytes per minute or roughly 2TB/s.  If
254      * you have an entropy source capable of generating more entropy than this
255      * and you can pass it through via virtio-rng, then hats off to you.  Until
256      * then, this is unlimited for all practical purposes.
257      */
258     DEFINE_PROP_UINT64("max-bytes", VirtIORNG, conf.max_bytes, INT64_MAX),
259     DEFINE_PROP_UINT32("period", VirtIORNG, conf.period_ms, 1 << 16),
260     DEFINE_PROP_LINK("rng", VirtIORNG, conf.rng, TYPE_RNG_BACKEND, RngBackend *),
261     DEFINE_PROP_END_OF_LIST(),
262 };
263 
virtio_rng_class_init(ObjectClass * klass,void * data)264 static void virtio_rng_class_init(ObjectClass *klass, void *data)
265 {
266     DeviceClass *dc = DEVICE_CLASS(klass);
267     VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
268 
269     device_class_set_props(dc, virtio_rng_properties);
270     dc->vmsd = &vmstate_virtio_rng;
271     set_bit(DEVICE_CATEGORY_MISC, dc->categories);
272     vdc->realize = virtio_rng_device_realize;
273     vdc->unrealize = virtio_rng_device_unrealize;
274     vdc->get_features = get_features;
275     vdc->set_status = virtio_rng_set_status;
276 }
277 
278 static const TypeInfo virtio_rng_info = {
279     .name = TYPE_VIRTIO_RNG,
280     .parent = TYPE_VIRTIO_DEVICE,
281     .instance_size = sizeof(VirtIORNG),
282     .class_init = virtio_rng_class_init,
283 };
284 
virtio_register_types(void)285 static void virtio_register_types(void)
286 {
287     type_register_static(&virtio_rng_info);
288 }
289 
290 type_init(virtio_register_types)
291