1 /*
2  * Randomness driver for virtio
3  *  Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
4  *
5  *  This program is free software; you can redistribute it and/or modify
6  *  it under the terms of the GNU General Public License as published by
7  *  the Free Software Foundation; either version 2 of the License, or
8  *  (at your option) any later version.
9  *
10  *  This program is distributed in the hope that it will be useful,
11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13  *  GNU General Public License for more details.
14  *
15  *  You should have received a copy of the GNU General Public License
16  *  along with this program; if not, write to the Free Software
17  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
18  */
19 
20 #include <linux/err.h>
21 #include <linux/hw_random.h>
22 #include <linux/scatterlist.h>
23 #include <linux/spinlock.h>
24 #include <linux/virtio.h>
25 #include <linux/virtio_rng.h>
26 #include <linux/module.h>
27 
28 static struct virtqueue *vq;
29 static unsigned int data_avail;
30 static DECLARE_COMPLETION(have_data);
31 static bool busy;
32 
33 static void random_recv_done(struct virtqueue *vq)
34 {
35 	/* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
36 	if (!virtqueue_get_buf(vq, &data_avail))
37 		return;
38 
39 	complete(&have_data);
40 }
41 
42 /* The host will fill any buffer we give it with sweet, sweet randomness. */
43 static void register_buffer(u8 *buf, size_t size)
44 {
45 	struct scatterlist sg;
46 
47 	sg_init_one(&sg, buf, size);
48 
49 	/* There should always be room for one buffer. */
50 	if (virtqueue_add_buf(vq, &sg, 0, 1, buf, GFP_KERNEL) < 0)
51 		BUG();
52 
53 	virtqueue_kick(vq);
54 }
55 
56 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
57 {
58 	int ret;
59 
60 	if (!busy) {
61 		busy = true;
62 		init_completion(&have_data);
63 		register_buffer(buf, size);
64 	}
65 
66 	if (!wait)
67 		return 0;
68 
69 	ret = wait_for_completion_killable(&have_data);
70 	if (ret < 0)
71 		return ret;
72 
73 	busy = false;
74 
75 	return data_avail;
76 }
77 
78 static void virtio_cleanup(struct hwrng *rng)
79 {
80 	if (busy)
81 		wait_for_completion(&have_data);
82 }
83 
84 
85 static struct hwrng virtio_hwrng = {
86 	.name		= "virtio",
87 	.cleanup	= virtio_cleanup,
88 	.read		= virtio_read,
89 };
90 
91 static int probe_common(struct virtio_device *vdev)
92 {
93 	int err;
94 
95 	/* We expect a single virtqueue. */
96 	vq = virtio_find_single_vq(vdev, random_recv_done, "input");
97 	if (IS_ERR(vq))
98 		return PTR_ERR(vq);
99 
100 	err = hwrng_register(&virtio_hwrng);
101 	if (err) {
102 		vdev->config->del_vqs(vdev);
103 		return err;
104 	}
105 
106 	return 0;
107 }
108 
109 static void remove_common(struct virtio_device *vdev)
110 {
111 	vdev->config->reset(vdev);
112 	busy = false;
113 	hwrng_unregister(&virtio_hwrng);
114 	vdev->config->del_vqs(vdev);
115 }
116 
117 static int virtrng_probe(struct virtio_device *vdev)
118 {
119 	return probe_common(vdev);
120 }
121 
122 static void virtrng_remove(struct virtio_device *vdev)
123 {
124 	remove_common(vdev);
125 }
126 
127 #ifdef CONFIG_PM
128 static int virtrng_freeze(struct virtio_device *vdev)
129 {
130 	remove_common(vdev);
131 	return 0;
132 }
133 
134 static int virtrng_restore(struct virtio_device *vdev)
135 {
136 	return probe_common(vdev);
137 }
138 #endif
139 
140 static struct virtio_device_id id_table[] = {
141 	{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
142 	{ 0 },
143 };
144 
145 static struct virtio_driver virtio_rng_driver = {
146 	.driver.name =	KBUILD_MODNAME,
147 	.driver.owner =	THIS_MODULE,
148 	.id_table =	id_table,
149 	.probe =	virtrng_probe,
150 	.remove =	virtrng_remove,
151 #ifdef CONFIG_PM
152 	.freeze =	virtrng_freeze,
153 	.restore =	virtrng_restore,
154 #endif
155 };
156 
157 static int __init init(void)
158 {
159 	return register_virtio_driver(&virtio_rng_driver);
160 }
161 
162 static void __exit fini(void)
163 {
164 	unregister_virtio_driver(&virtio_rng_driver);
165 }
166 module_init(init);
167 module_exit(fini);
168 
169 MODULE_DEVICE_TABLE(virtio, id_table);
170 MODULE_DESCRIPTION("Virtio random number driver");
171 MODULE_LICENSE("GPL");
172