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 
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. */
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 
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 
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 
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 
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 
146 static int virtrng_probe(struct virtio_device *vdev)
147 {
148 	return probe_common(vdev);
149 }
150 
151 static void virtrng_remove(struct virtio_device *vdev)
152 {
153 	remove_common(vdev);
154 }
155 
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
167 static int virtrng_freeze(struct virtio_device *vdev)
168 {
169 	remove_common(vdev);
170 	return 0;
171 }
172 
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