xref: /qemu/backends/rng-random.c (revision 6402cbbb)
1 /*
2  * QEMU Random Number Generator Backend
3  *
4  * Copyright IBM, Corp. 2012
5  *
6  * Authors:
7  *  Anthony Liguori   <aliguori@us.ibm.com>
8  *
9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
10  * See the COPYING file in the top-level directory.
11  */
12 
13 #include "qemu/osdep.h"
14 #include "sysemu/rng-random.h"
15 #include "sysemu/rng.h"
16 #include "qapi/error.h"
17 #include "qapi/qmp/qerror.h"
18 #include "qemu/main-loop.h"
19 
20 struct RngRandom
21 {
22     RngBackend parent;
23 
24     int fd;
25     char *filename;
26 };
27 
28 /**
29  * A simple and incomplete backend to request entropy from /dev/random.
30  *
31  * This backend exposes an additional "filename" property that can be used to
32  * set the filename to use to open the backend.
33  */
34 
35 static void entropy_available(void *opaque)
36 {
37     RngRandom *s = RNG_RANDOM(opaque);
38 
39     while (!QSIMPLEQ_EMPTY(&s->parent.requests)) {
40         RngRequest *req = QSIMPLEQ_FIRST(&s->parent.requests);
41         ssize_t len;
42 
43         len = read(s->fd, req->data, req->size);
44         if (len < 0 && errno == EAGAIN) {
45             return;
46         }
47         g_assert(len != -1);
48 
49         req->receive_entropy(req->opaque, req->data, len);
50 
51         rng_backend_finalize_request(&s->parent, req);
52     }
53 
54     /* We've drained all requests, the fd handler can be reset. */
55     qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
56 }
57 
58 static void rng_random_request_entropy(RngBackend *b, RngRequest *req)
59 {
60     RngRandom *s = RNG_RANDOM(b);
61 
62     if (QSIMPLEQ_EMPTY(&s->parent.requests)) {
63         /* If there are no pending requests yet, we need to
64          * install our fd handler. */
65         qemu_set_fd_handler(s->fd, entropy_available, NULL, s);
66     }
67 }
68 
69 static void rng_random_opened(RngBackend *b, Error **errp)
70 {
71     RngRandom *s = RNG_RANDOM(b);
72 
73     if (s->filename == NULL) {
74         error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
75                    "filename", "a valid filename");
76     } else {
77         s->fd = qemu_open(s->filename, O_RDONLY | O_NONBLOCK);
78         if (s->fd == -1) {
79             error_setg_file_open(errp, errno, s->filename);
80         }
81     }
82 }
83 
84 static char *rng_random_get_filename(Object *obj, Error **errp)
85 {
86     RngRandom *s = RNG_RANDOM(obj);
87 
88     return g_strdup(s->filename);
89 }
90 
91 static void rng_random_set_filename(Object *obj, const char *filename,
92                                  Error **errp)
93 {
94     RngBackend *b = RNG_BACKEND(obj);
95     RngRandom *s = RNG_RANDOM(obj);
96 
97     if (b->opened) {
98         error_setg(errp, QERR_PERMISSION_DENIED);
99         return;
100     }
101 
102     g_free(s->filename);
103     s->filename = g_strdup(filename);
104 }
105 
106 static void rng_random_init(Object *obj)
107 {
108     RngRandom *s = RNG_RANDOM(obj);
109 
110     object_property_add_str(obj, "filename",
111                             rng_random_get_filename,
112                             rng_random_set_filename,
113                             NULL);
114 
115     s->filename = g_strdup("/dev/random");
116     s->fd = -1;
117 }
118 
119 static void rng_random_finalize(Object *obj)
120 {
121     RngRandom *s = RNG_RANDOM(obj);
122 
123     if (s->fd != -1) {
124         qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
125         qemu_close(s->fd);
126     }
127 
128     g_free(s->filename);
129 }
130 
131 static void rng_random_class_init(ObjectClass *klass, void *data)
132 {
133     RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
134 
135     rbc->request_entropy = rng_random_request_entropy;
136     rbc->opened = rng_random_opened;
137 }
138 
139 static const TypeInfo rng_random_info = {
140     .name = TYPE_RNG_RANDOM,
141     .parent = TYPE_RNG_BACKEND,
142     .instance_size = sizeof(RngRandom),
143     .class_init = rng_random_class_init,
144     .instance_init = rng_random_init,
145     .instance_finalize = rng_random_finalize,
146 };
147 
148 static void register_types(void)
149 {
150     type_register_static(&rng_random_info);
151 }
152 
153 type_init(register_types);
154