1 /*
2  * Non-physical true random number generator based on timing jitter --
3  * Linux Kernel Crypto API specific code
4  *
5  * Copyright Stephan Mueller <smueller@chronox.de>, 2015
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, and the entire permission notice in its entirety,
12  *    including the disclaimer of warranties.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. The name of the author may not be used to endorse or promote
17  *    products derived from this software without specific prior
18  *    written permission.
19  *
20  * ALTERNATIVELY, this product may be distributed under the terms of
21  * the GNU General Public License, in which case the provisions of the GPL2 are
22  * required INSTEAD OF the above restrictions.  (This clause is
23  * necessary due to a potential bad interaction between the GPL and
24  * the restrictions contained in a BSD-style copyright.)
25  *
26  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
27  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
29  * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
30  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
31  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
32  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
33  * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
34  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
35  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
36  * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
37  * DAMAGE.
38  */
39 
40 #include <linux/module.h>
41 #include <linux/slab.h>
42 #include <linux/fips.h>
43 #include <linux/time.h>
44 #include <linux/crypto.h>
45 #include <crypto/internal/rng.h>
46 
47 struct rand_data;
48 int jent_read_entropy(struct rand_data *ec, unsigned char *data,
49 		      unsigned int len);
50 int jent_entropy_init(void);
51 struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
52 					       unsigned int flags);
53 void jent_entropy_collector_free(struct rand_data *entropy_collector);
54 
55 /***************************************************************************
56  * Helper function
57  ***************************************************************************/
58 
59 void *jent_zalloc(unsigned int len)
60 {
61 	return kzalloc(len, GFP_KERNEL);
62 }
63 
64 void jent_zfree(void *ptr)
65 {
66 	kzfree(ptr);
67 }
68 
69 int jent_fips_enabled(void)
70 {
71 	return fips_enabled;
72 }
73 
74 void jent_panic(char *s)
75 {
76 	panic("%s", s);
77 }
78 
79 void jent_memcpy(void *dest, const void *src, unsigned int n)
80 {
81 	memcpy(dest, src, n);
82 }
83 
84 /*
85  * Obtain a high-resolution time stamp value. The time stamp is used to measure
86  * the execution time of a given code path and its variations. Hence, the time
87  * stamp must have a sufficiently high resolution.
88  *
89  * Note, if the function returns zero because a given architecture does not
90  * implement a high-resolution time stamp, the RNG code's runtime test
91  * will detect it and will not produce output.
92  */
93 void jent_get_nstime(__u64 *out)
94 {
95 	__u64 tmp = 0;
96 
97 	tmp = random_get_entropy();
98 
99 	/*
100 	 * If random_get_entropy does not return a value, i.e. it is not
101 	 * implemented for a given architecture, use a clock source.
102 	 * hoping that there are timers we can work with.
103 	 */
104 	if (tmp == 0)
105 		tmp = ktime_get_ns();
106 
107 	*out = tmp;
108 }
109 
110 /***************************************************************************
111  * Kernel crypto API interface
112  ***************************************************************************/
113 
114 struct jitterentropy {
115 	spinlock_t jent_lock;
116 	struct rand_data *entropy_collector;
117 };
118 
119 static int jent_kcapi_init(struct crypto_tfm *tfm)
120 {
121 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
122 	int ret = 0;
123 
124 	rng->entropy_collector = jent_entropy_collector_alloc(1, 0);
125 	if (!rng->entropy_collector)
126 		ret = -ENOMEM;
127 
128 	spin_lock_init(&rng->jent_lock);
129 	return ret;
130 }
131 
132 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
133 {
134 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
135 
136 	spin_lock(&rng->jent_lock);
137 	if (rng->entropy_collector)
138 		jent_entropy_collector_free(rng->entropy_collector);
139 	rng->entropy_collector = NULL;
140 	spin_unlock(&rng->jent_lock);
141 }
142 
143 static int jent_kcapi_random(struct crypto_rng *tfm,
144 			     const u8 *src, unsigned int slen,
145 			     u8 *rdata, unsigned int dlen)
146 {
147 	struct jitterentropy *rng = crypto_rng_ctx(tfm);
148 	int ret = 0;
149 
150 	spin_lock(&rng->jent_lock);
151 	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
152 	spin_unlock(&rng->jent_lock);
153 
154 	return ret;
155 }
156 
157 static int jent_kcapi_reset(struct crypto_rng *tfm,
158 			    const u8 *seed, unsigned int slen)
159 {
160 	return 0;
161 }
162 
163 static struct rng_alg jent_alg = {
164 	.generate		= jent_kcapi_random,
165 	.seed			= jent_kcapi_reset,
166 	.seedsize		= 0,
167 	.base			= {
168 		.cra_name               = "jitterentropy_rng",
169 		.cra_driver_name        = "jitterentropy_rng",
170 		.cra_priority           = 100,
171 		.cra_ctxsize            = sizeof(struct jitterentropy),
172 		.cra_module             = THIS_MODULE,
173 		.cra_init               = jent_kcapi_init,
174 		.cra_exit               = jent_kcapi_cleanup,
175 
176 	}
177 };
178 
179 static int __init jent_mod_init(void)
180 {
181 	int ret = 0;
182 
183 	ret = jent_entropy_init();
184 	if (ret) {
185 		pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
186 		return -EFAULT;
187 	}
188 	return crypto_register_rng(&jent_alg);
189 }
190 
191 static void __exit jent_mod_exit(void)
192 {
193 	crypto_unregister_rng(&jent_alg);
194 }
195 
196 module_init(jent_mod_init);
197 module_exit(jent_mod_exit);
198 
199 MODULE_LICENSE("Dual BSD/GPL");
200 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
201 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
202 MODULE_ALIAS_CRYPTO("jitterentropy_rng");
203