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 
17 static DEFINE_IDA(rng_index_ida);
18 
19 struct 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 
38 static 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 
51 static 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 
66 static 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 
78 static 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 
122 static 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 
129 static 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_simple_get(&rng_index_ida, 0, 0, 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 
168 err_find:
169 	ida_simple_remove(&rng_index_ida, index);
170 err_ida:
171 	kfree(vi);
172 	return err;
173 }
174 
175 static 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_simple_remove(&rng_index_ida, vi->index);
188 	kfree(vi);
189 }
190 
191 static int virtrng_probe(struct virtio_device *vdev)
192 {
193 	return probe_common(vdev);
194 }
195 
196 static void virtrng_remove(struct virtio_device *vdev)
197 {
198 	remove_common(vdev);
199 }
200 
201 static 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 
211 #ifdef CONFIG_PM_SLEEP
212 static int virtrng_freeze(struct virtio_device *vdev)
213 {
214 	remove_common(vdev);
215 	return 0;
216 }
217 
218 static int virtrng_restore(struct virtio_device *vdev)
219 {
220 	int err;
221 
222 	err = probe_common(vdev);
223 	if (!err) {
224 		struct virtrng_info *vi = vdev->priv;
225 
226 		/*
227 		 * Set hwrng_removed to ensure that virtio_read()
228 		 * does not block waiting for data before the
229 		 * registration is complete.
230 		 */
231 		vi->hwrng_removed = true;
232 		err = hwrng_register(&vi->hwrng);
233 		if (!err) {
234 			vi->hwrng_register_done = true;
235 			vi->hwrng_removed = false;
236 		}
237 	}
238 
239 	return err;
240 }
241 #endif
242 
243 static const struct virtio_device_id id_table[] = {
244 	{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
245 	{ 0 },
246 };
247 
248 static struct virtio_driver virtio_rng_driver = {
249 	.driver.name =	KBUILD_MODNAME,
250 	.driver.owner =	THIS_MODULE,
251 	.id_table =	id_table,
252 	.probe =	virtrng_probe,
253 	.remove =	virtrng_remove,
254 	.scan =		virtrng_scan,
255 #ifdef CONFIG_PM_SLEEP
256 	.freeze =	virtrng_freeze,
257 	.restore =	virtrng_restore,
258 #endif
259 };
260 
261 module_virtio_driver(virtio_rng_driver);
262 MODULE_DEVICE_TABLE(virtio, id_table);
263 MODULE_DESCRIPTION("Virtio random number driver");
264 MODULE_LICENSE("GPL");
265