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 #include "jitterentropy.h"
48 
49 /***************************************************************************
50  * Helper function
51  ***************************************************************************/
52 
53 void *jent_zalloc(unsigned int len)
54 {
55 	return kzalloc(len, GFP_KERNEL);
56 }
57 
58 void jent_zfree(void *ptr)
59 {
60 	kzfree(ptr);
61 }
62 
63 int jent_fips_enabled(void)
64 {
65 	return fips_enabled;
66 }
67 
68 void jent_panic(char *s)
69 {
70 	panic("%s", s);
71 }
72 
73 void jent_memcpy(void *dest, const void *src, unsigned int n)
74 {
75 	memcpy(dest, src, n);
76 }
77 
78 /*
79  * Obtain a high-resolution time stamp value. The time stamp is used to measure
80  * the execution time of a given code path and its variations. Hence, the time
81  * stamp must have a sufficiently high resolution.
82  *
83  * Note, if the function returns zero because a given architecture does not
84  * implement a high-resolution time stamp, the RNG code's runtime test
85  * will detect it and will not produce output.
86  */
87 void jent_get_nstime(__u64 *out)
88 {
89 	__u64 tmp = 0;
90 
91 	tmp = random_get_entropy();
92 
93 	/*
94 	 * If random_get_entropy does not return a value, i.e. it is not
95 	 * implemented for a given architecture, use a clock source.
96 	 * hoping that there are timers we can work with.
97 	 */
98 	if (tmp == 0)
99 		tmp = ktime_get_ns();
100 
101 	*out = tmp;
102 }
103 
104 /***************************************************************************
105  * Kernel crypto API interface
106  ***************************************************************************/
107 
108 struct jitterentropy {
109 	spinlock_t jent_lock;
110 	struct rand_data *entropy_collector;
111 };
112 
113 static int jent_kcapi_init(struct crypto_tfm *tfm)
114 {
115 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
116 	int ret = 0;
117 
118 	rng->entropy_collector = jent_entropy_collector_alloc(1, 0);
119 	if (!rng->entropy_collector)
120 		ret = -ENOMEM;
121 
122 	spin_lock_init(&rng->jent_lock);
123 	return ret;
124 }
125 
126 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
127 {
128 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
129 
130 	spin_lock(&rng->jent_lock);
131 	if (rng->entropy_collector)
132 		jent_entropy_collector_free(rng->entropy_collector);
133 	rng->entropy_collector = NULL;
134 	spin_unlock(&rng->jent_lock);
135 }
136 
137 static int jent_kcapi_random(struct crypto_rng *tfm,
138 			     const u8 *src, unsigned int slen,
139 			     u8 *rdata, unsigned int dlen)
140 {
141 	struct jitterentropy *rng = crypto_rng_ctx(tfm);
142 	int ret = 0;
143 
144 	spin_lock(&rng->jent_lock);
145 	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
146 	spin_unlock(&rng->jent_lock);
147 
148 	return ret;
149 }
150 
151 static int jent_kcapi_reset(struct crypto_rng *tfm,
152 			    const u8 *seed, unsigned int slen)
153 {
154 	return 0;
155 }
156 
157 static struct rng_alg jent_alg = {
158 	.generate		= jent_kcapi_random,
159 	.seed			= jent_kcapi_reset,
160 	.seedsize		= 0,
161 	.base			= {
162 		.cra_name               = "jitterentropy_rng",
163 		.cra_driver_name        = "jitterentropy_rng",
164 		.cra_priority           = 100,
165 		.cra_ctxsize            = sizeof(struct jitterentropy),
166 		.cra_module             = THIS_MODULE,
167 		.cra_init               = jent_kcapi_init,
168 		.cra_exit               = jent_kcapi_cleanup,
169 
170 	}
171 };
172 
173 static int __init jent_mod_init(void)
174 {
175 	int ret = 0;
176 
177 	ret = jent_entropy_init();
178 	if (ret) {
179 		pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
180 		return -EFAULT;
181 	}
182 	return crypto_register_rng(&jent_alg);
183 }
184 
185 static void __exit jent_mod_exit(void)
186 {
187 	crypto_unregister_rng(&jent_alg);
188 }
189 
190 module_init(jent_mod_init);
191 module_exit(jent_mod_exit);
192 
193 MODULE_LICENSE("Dual BSD/GPL");
194 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
195 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
196 MODULE_ALIAS_CRYPTO("jitterentropy_rng");
197