1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Randomness driver for virtio
4 * Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
5 */
6
7 #include <linux/err.h>
8 #include <linux/hw_random.h>
9 #include <linux/scatterlist.h>
10 #include <linux/spinlock.h>
11 #include <linux/virtio.h>
12 #include <linux/virtio_rng.h>
13 #include <linux/module.h>
14 #include <linux/slab.h>
15
16 static DEFINE_IDA(rng_index_ida);
17
18 struct virtrng_info {
19 struct hwrng hwrng;
20 struct virtqueue *vq;
21 struct completion have_data;
22 char name[25];
23 unsigned int data_avail;
24 int index;
25 bool busy;
26 bool hwrng_register_done;
27 bool hwrng_removed;
28 };
29
random_recv_done(struct virtqueue * vq)30 static void random_recv_done(struct virtqueue *vq)
31 {
32 struct virtrng_info *vi = vq->vdev->priv;
33
34 /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
35 if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
36 return;
37
38 complete(&vi->have_data);
39 }
40
41 /* The host will fill any buffer we give it with sweet, sweet randomness. */
register_buffer(struct virtrng_info * vi,u8 * buf,size_t size)42 static void register_buffer(struct virtrng_info *vi, u8 *buf, size_t size)
43 {
44 struct scatterlist sg;
45
46 sg_init_one(&sg, buf, size);
47
48 /* There should always be room for one buffer. */
49 virtqueue_add_inbuf(vi->vq, &sg, 1, buf, GFP_KERNEL);
50
51 virtqueue_kick(vi->vq);
52 }
53
virtio_read(struct hwrng * rng,void * buf,size_t size,bool wait)54 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
55 {
56 int ret;
57 struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
58
59 if (vi->hwrng_removed)
60 return -ENODEV;
61
62 if (!vi->busy) {
63 vi->busy = true;
64 reinit_completion(&vi->have_data);
65 register_buffer(vi, buf, size);
66 }
67
68 if (!wait)
69 return 0;
70
71 ret = wait_for_completion_killable(&vi->have_data);
72 if (ret < 0)
73 return ret;
74
75 vi->busy = false;
76
77 return vi->data_avail;
78 }
79
virtio_cleanup(struct hwrng * rng)80 static void virtio_cleanup(struct hwrng *rng)
81 {
82 struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
83
84 if (vi->busy)
85 wait_for_completion(&vi->have_data);
86 }
87
probe_common(struct virtio_device * vdev)88 static int probe_common(struct virtio_device *vdev)
89 {
90 int err, index;
91 struct virtrng_info *vi = NULL;
92
93 vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
94 if (!vi)
95 return -ENOMEM;
96
97 vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
98 if (index < 0) {
99 err = index;
100 goto err_ida;
101 }
102 sprintf(vi->name, "virtio_rng.%d", index);
103 init_completion(&vi->have_data);
104
105 vi->hwrng = (struct hwrng) {
106 .read = virtio_read,
107 .cleanup = virtio_cleanup,
108 .priv = (unsigned long)vi,
109 .name = vi->name,
110 .quality = 1000,
111 };
112 vdev->priv = vi;
113
114 /* We expect a single virtqueue. */
115 vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
116 if (IS_ERR(vi->vq)) {
117 err = PTR_ERR(vi->vq);
118 goto err_find;
119 }
120
121 return 0;
122
123 err_find:
124 ida_simple_remove(&rng_index_ida, index);
125 err_ida:
126 kfree(vi);
127 return err;
128 }
129
remove_common(struct virtio_device * vdev)130 static void remove_common(struct virtio_device *vdev)
131 {
132 struct virtrng_info *vi = vdev->priv;
133
134 vi->hwrng_removed = true;
135 vi->data_avail = 0;
136 complete(&vi->have_data);
137 vdev->config->reset(vdev);
138 vi->busy = false;
139 if (vi->hwrng_register_done)
140 hwrng_unregister(&vi->hwrng);
141 vdev->config->del_vqs(vdev);
142 ida_simple_remove(&rng_index_ida, vi->index);
143 kfree(vi);
144 }
145
virtrng_probe(struct virtio_device * vdev)146 static int virtrng_probe(struct virtio_device *vdev)
147 {
148 return probe_common(vdev);
149 }
150
virtrng_remove(struct virtio_device * vdev)151 static void virtrng_remove(struct virtio_device *vdev)
152 {
153 remove_common(vdev);
154 }
155
virtrng_scan(struct virtio_device * vdev)156 static void virtrng_scan(struct virtio_device *vdev)
157 {
158 struct virtrng_info *vi = vdev->priv;
159 int err;
160
161 err = hwrng_register(&vi->hwrng);
162 if (!err)
163 vi->hwrng_register_done = true;
164 }
165
166 #ifdef CONFIG_PM_SLEEP
virtrng_freeze(struct virtio_device * vdev)167 static int virtrng_freeze(struct virtio_device *vdev)
168 {
169 remove_common(vdev);
170 return 0;
171 }
172
virtrng_restore(struct virtio_device * vdev)173 static int virtrng_restore(struct virtio_device *vdev)
174 {
175 int err;
176
177 err = probe_common(vdev);
178 if (!err) {
179 struct virtrng_info *vi = vdev->priv;
180
181 /*
182 * Set hwrng_removed to ensure that virtio_read()
183 * does not block waiting for data before the
184 * registration is complete.
185 */
186 vi->hwrng_removed = true;
187 err = hwrng_register(&vi->hwrng);
188 if (!err) {
189 vi->hwrng_register_done = true;
190 vi->hwrng_removed = false;
191 }
192 }
193
194 return err;
195 }
196 #endif
197
198 static const struct virtio_device_id id_table[] = {
199 { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
200 { 0 },
201 };
202
203 static struct virtio_driver virtio_rng_driver = {
204 .driver.name = KBUILD_MODNAME,
205 .driver.owner = THIS_MODULE,
206 .id_table = id_table,
207 .probe = virtrng_probe,
208 .remove = virtrng_remove,
209 .scan = virtrng_scan,
210 #ifdef CONFIG_PM_SLEEP
211 .freeze = virtrng_freeze,
212 .restore = virtrng_restore,
213 #endif
214 };
215
216 module_virtio_driver(virtio_rng_driver);
217 MODULE_DEVICE_TABLE(virtio, id_table);
218 MODULE_DESCRIPTION("Virtio random number driver");
219 MODULE_LICENSE("GPL");
220
