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 <asm/barrier.h>
8#include <linux/err.h>
9#include <linux/hw_random.h>
10#include <linux/scatterlist.h>
11#include <linux/spinlock.h>
12#include <linux/virtio.h>
13#include <linux/virtio_rng.h>
14#include <linux/module.h>
15#include <linux/slab.h>
16
17static DEFINE_IDA(rng_index_ida);
18
19struct virtrng_info {
20	struct hwrng hwrng;
21	struct virtqueue *vq;
22	char name[25];
23	int index;
24	bool hwrng_register_done;
25	bool hwrng_removed;
26	/* data transfer */
27	struct completion have_data;
28	unsigned int data_avail;
29	unsigned int data_idx;
30	/* minimal size returned by rng_buffer_size() */
31#if SMP_CACHE_BYTES < 32
32	u8 data[32];
33#else
34	u8 data[SMP_CACHE_BYTES];
35#endif
36};
37
38static void random_recv_done(struct virtqueue *vq)
39{
40	struct virtrng_info *vi = vq->vdev->priv;
41	unsigned int len;
42
43	/* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
44	if (!virtqueue_get_buf(vi->vq, &len))
45		return;
46
47	smp_store_release(&vi->data_avail, len);
48	complete(&vi->have_data);
49}
50
51static void request_entropy(struct virtrng_info *vi)
52{
53	struct scatterlist sg;
54
55	reinit_completion(&vi->have_data);
56	vi->data_idx = 0;
57
58	sg_init_one(&sg, vi->data, sizeof(vi->data));
59
60	/* There should always be room for one buffer. */
61	virtqueue_add_inbuf(vi->vq, &sg, 1, vi->data, GFP_KERNEL);
62
63	virtqueue_kick(vi->vq);
64}
65
66static unsigned int copy_data(struct virtrng_info *vi, void *buf,
67			      unsigned int size)
68{
69	size = min_t(unsigned int, size, vi->data_avail);
70	memcpy(buf, vi->data + vi->data_idx, size);
71	vi->data_idx += size;
72	vi->data_avail -= size;
73	if (vi->data_avail == 0)
74		request_entropy(vi);
75	return size;
76}
77
78static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
79{
80	int ret;
81	struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
82	unsigned int chunk;
83	size_t read;
84
85	if (vi->hwrng_removed)
86		return -ENODEV;
87
88	read = 0;
89
90	/* copy available data */
91	if (smp_load_acquire(&vi->data_avail)) {
92		chunk = copy_data(vi, buf, size);
93		size -= chunk;
94		read += chunk;
95	}
96
97	if (!wait)
98		return read;
99
100	/* We have already copied available entropy,
101	 * so either size is 0 or data_avail is 0
102	 */
103	while (size != 0) {
104		/* data_avail is 0 but a request is pending */
105		ret = wait_for_completion_killable(&vi->have_data);
106		if (ret < 0)
107			return ret;
108		/* if vi->data_avail is 0, we have been interrupted
109		 * by a cleanup, but buffer stays in the queue
110		 */
111		if (vi->data_avail == 0)
112			return read;
113
114		chunk = copy_data(vi, buf + read, size);
115		size -= chunk;
116		read += chunk;
117	}
118
119	return read;
120}
121
122static void virtio_cleanup(struct hwrng *rng)
123{
124	struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
125
126	complete(&vi->have_data);
127}
128
129static int probe_common(struct virtio_device *vdev)
130{
131	int err, index;
132	struct virtrng_info *vi = NULL;
133
134	vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
135	if (!vi)
136		return -ENOMEM;
137
138	vi->index = index = ida_alloc(&rng_index_ida, GFP_KERNEL);
139	if (index < 0) {
140		err = index;
141		goto err_ida;
142	}
143	sprintf(vi->name, "virtio_rng.%d", index);
144	init_completion(&vi->have_data);
145
146	vi->hwrng = (struct hwrng) {
147		.read = virtio_read,
148		.cleanup = virtio_cleanup,
149		.priv = (unsigned long)vi,
150		.name = vi->name,
151	};
152	vdev->priv = vi;
153
154	/* We expect a single virtqueue. */
155	vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
156	if (IS_ERR(vi->vq)) {
157		err = PTR_ERR(vi->vq);
158		goto err_find;
159	}
160
161	virtio_device_ready(vdev);
162
163	/* we always have a pending entropy request */
164	request_entropy(vi);
165
166	return 0;
167
168err_find:
169	ida_free(&rng_index_ida, index);
170err_ida:
171	kfree(vi);
172	return err;
173}
174
175static void remove_common(struct virtio_device *vdev)
176{
177	struct virtrng_info *vi = vdev->priv;
178
179	vi->hwrng_removed = true;
180	vi->data_avail = 0;
181	vi->data_idx = 0;
182	complete(&vi->have_data);
183	if (vi->hwrng_register_done)
184		hwrng_unregister(&vi->hwrng);
185	virtio_reset_device(vdev);
186	vdev->config->del_vqs(vdev);
187	ida_free(&rng_index_ida, vi->index);
188	kfree(vi);
189}
190
191static int virtrng_probe(struct virtio_device *vdev)
192{
193	return probe_common(vdev);
194}
195
196static void virtrng_remove(struct virtio_device *vdev)
197{
198	remove_common(vdev);
199}
200
201static void virtrng_scan(struct virtio_device *vdev)
202{
203	struct virtrng_info *vi = vdev->priv;
204	int err;
205
206	err = hwrng_register(&vi->hwrng);
207	if (!err)
208		vi->hwrng_register_done = true;
209}
210
211static int virtrng_freeze(struct virtio_device *vdev)
212{
213	remove_common(vdev);
214	return 0;
215}
216
217static int virtrng_restore(struct virtio_device *vdev)
218{
219	int err;
220
221	err = probe_common(vdev);
222	if (!err) {
223		struct virtrng_info *vi = vdev->priv;
224
225		/*
226		 * Set hwrng_removed to ensure that virtio_read()
227		 * does not block waiting for data before the
228		 * registration is complete.
229		 */
230		vi->hwrng_removed = true;
231		err = hwrng_register(&vi->hwrng);
232		if (!err) {
233			vi->hwrng_register_done = true;
234			vi->hwrng_removed = false;
235		}
236	}
237
238	return err;
239}
240
241static const struct virtio_device_id id_table[] = {
242	{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
243	{ 0 },
244};
245
246static struct virtio_driver virtio_rng_driver = {
247	.driver.name =	KBUILD_MODNAME,
248	.id_table =	id_table,
249	.probe =	virtrng_probe,
250	.remove =	virtrng_remove,
251	.scan =		virtrng_scan,
252	.freeze =	pm_sleep_ptr(virtrng_freeze),
253	.restore =	pm_sleep_ptr(virtrng_restore),
254};
255
256module_virtio_driver(virtio_rng_driver);
257MODULE_DEVICE_TABLE(virtio, id_table);
258MODULE_DESCRIPTION("Virtio random number driver");
259MODULE_LICENSE("GPL");
260