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 __u64 jent_rol64(__u64 word, unsigned int shift)
60 {
61 	return rol64(word, shift);
62 }
63 
64 void *jent_zalloc(unsigned int len)
65 {
66 	return kzalloc(len, GFP_KERNEL);
67 }
68 
69 void jent_zfree(void *ptr)
70 {
71 	kzfree(ptr);
72 }
73 
74 int jent_fips_enabled(void)
75 {
76 	return fips_enabled;
77 }
78 
79 void jent_panic(char *s)
80 {
81 	panic("%s", s);
82 }
83 
84 void jent_memcpy(void *dest, const void *src, unsigned int n)
85 {
86 	memcpy(dest, src, n);
87 }
88 
89 /*
90  * Obtain a high-resolution time stamp value. The time stamp is used to measure
91  * the execution time of a given code path and its variations. Hence, the time
92  * stamp must have a sufficiently high resolution.
93  *
94  * Note, if the function returns zero because a given architecture does not
95  * implement a high-resolution time stamp, the RNG code's runtime test
96  * will detect it and will not produce output.
97  */
98 void jent_get_nstime(__u64 *out)
99 {
100 	__u64 tmp = 0;
101 
102 	tmp = random_get_entropy();
103 
104 	/*
105 	 * If random_get_entropy does not return a value, i.e. it is not
106 	 * implemented for a given architecture, use a clock source.
107 	 * hoping that there are timers we can work with.
108 	 */
109 	if (tmp == 0)
110 		tmp = ktime_get_ns();
111 
112 	*out = tmp;
113 }
114 
115 /***************************************************************************
116  * Kernel crypto API interface
117  ***************************************************************************/
118 
119 struct jitterentropy {
120 	spinlock_t jent_lock;
121 	struct rand_data *entropy_collector;
122 };
123 
124 static int jent_kcapi_init(struct crypto_tfm *tfm)
125 {
126 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
127 	int ret = 0;
128 
129 	rng->entropy_collector = jent_entropy_collector_alloc(1, 0);
130 	if (!rng->entropy_collector)
131 		ret = -ENOMEM;
132 
133 	spin_lock_init(&rng->jent_lock);
134 	return ret;
135 }
136 
137 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
138 {
139 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
140 
141 	spin_lock(&rng->jent_lock);
142 	if (rng->entropy_collector)
143 		jent_entropy_collector_free(rng->entropy_collector);
144 	rng->entropy_collector = NULL;
145 	spin_unlock(&rng->jent_lock);
146 }
147 
148 static int jent_kcapi_random(struct crypto_rng *tfm,
149 			     const u8 *src, unsigned int slen,
150 			     u8 *rdata, unsigned int dlen)
151 {
152 	struct jitterentropy *rng = crypto_rng_ctx(tfm);
153 	int ret = 0;
154 
155 	spin_lock(&rng->jent_lock);
156 	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
157 	spin_unlock(&rng->jent_lock);
158 
159 	return ret;
160 }
161 
162 static int jent_kcapi_reset(struct crypto_rng *tfm,
163 			    const u8 *seed, unsigned int slen)
164 {
165 	return 0;
166 }
167 
168 static struct rng_alg jent_alg = {
169 	.generate		= jent_kcapi_random,
170 	.seed			= jent_kcapi_reset,
171 	.seedsize		= 0,
172 	.base			= {
173 		.cra_name               = "jitterentropy_rng",
174 		.cra_driver_name        = "jitterentropy_rng",
175 		.cra_priority           = 100,
176 		.cra_ctxsize            = sizeof(struct jitterentropy),
177 		.cra_module             = THIS_MODULE,
178 		.cra_init               = jent_kcapi_init,
179 		.cra_exit               = jent_kcapi_cleanup,
180 
181 	}
182 };
183 
184 static int __init jent_mod_init(void)
185 {
186 	int ret = 0;
187 
188 	ret = jent_entropy_init();
189 	if (ret) {
190 		pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
191 		return -EFAULT;
192 	}
193 	return crypto_register_rng(&jent_alg);
194 }
195 
196 static void __exit jent_mod_exit(void)
197 {
198 	crypto_unregister_rng(&jent_alg);
199 }
200 
201 module_init(jent_mod_init);
202 module_exit(jent_mod_exit);
203 
204 MODULE_LICENSE("Dual BSD/GPL");
205 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
206 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
207 MODULE_ALIAS_CRYPTO("jitterentropy_rng");
208