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 	unsigned int reset_cnt;
112 };
113 
114 static int jent_kcapi_init(struct crypto_tfm *tfm)
115 {
116 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
117 	int ret = 0;
118 
119 	rng->entropy_collector = jent_entropy_collector_alloc(1, 0);
120 	if (!rng->entropy_collector)
121 		ret = -ENOMEM;
122 
123 	spin_lock_init(&rng->jent_lock);
124 	return ret;
125 }
126 
127 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
128 {
129 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
130 
131 	spin_lock(&rng->jent_lock);
132 	if (rng->entropy_collector)
133 		jent_entropy_collector_free(rng->entropy_collector);
134 	rng->entropy_collector = NULL;
135 	spin_unlock(&rng->jent_lock);
136 }
137 
138 static int jent_kcapi_random(struct crypto_rng *tfm,
139 			     const u8 *src, unsigned int slen,
140 			     u8 *rdata, unsigned int dlen)
141 {
142 	struct jitterentropy *rng = crypto_rng_ctx(tfm);
143 	int ret = 0;
144 
145 	spin_lock(&rng->jent_lock);
146 
147 	/* Return a permanent error in case we had too many resets in a row. */
148 	if (rng->reset_cnt > (1<<10)) {
149 		ret = -EFAULT;
150 		goto out;
151 	}
152 
153 	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
154 
155 	/* Reset RNG in case of health failures */
156 	if (ret < -1) {
157 		pr_warn_ratelimited("Reset Jitter RNG due to health test failure: %s failure\n",
158 				    (ret == -2) ? "Repetition Count Test" :
159 						  "Adaptive Proportion Test");
160 
161 		rng->reset_cnt++;
162 
163 		ret = -EAGAIN;
164 	} else {
165 		rng->reset_cnt = 0;
166 
167 		/* Convert the Jitter RNG error into a usable error code */
168 		if (ret == -1)
169 			ret = -EINVAL;
170 	}
171 
172 out:
173 	spin_unlock(&rng->jent_lock);
174 
175 	return ret;
176 }
177 
178 static int jent_kcapi_reset(struct crypto_rng *tfm,
179 			    const u8 *seed, unsigned int slen)
180 {
181 	return 0;
182 }
183 
184 static struct rng_alg jent_alg = {
185 	.generate		= jent_kcapi_random,
186 	.seed			= jent_kcapi_reset,
187 	.seedsize		= 0,
188 	.base			= {
189 		.cra_name               = "jitterentropy_rng",
190 		.cra_driver_name        = "jitterentropy_rng",
191 		.cra_priority           = 100,
192 		.cra_ctxsize            = sizeof(struct jitterentropy),
193 		.cra_module             = THIS_MODULE,
194 		.cra_init               = jent_kcapi_init,
195 		.cra_exit               = jent_kcapi_cleanup,
196 
197 	}
198 };
199 
200 static int __init jent_mod_init(void)
201 {
202 	int ret = 0;
203 
204 	ret = jent_entropy_init();
205 	if (ret) {
206 		pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
207 		return -EFAULT;
208 	}
209 	return crypto_register_rng(&jent_alg);
210 }
211 
212 static void __exit jent_mod_exit(void)
213 {
214 	crypto_unregister_rng(&jent_alg);
215 }
216 
217 module_init(jent_mod_init);
218 module_exit(jent_mod_exit);
219 
220 MODULE_LICENSE("Dual BSD/GPL");
221 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
222 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
223 MODULE_ALIAS_CRYPTO("jitterentropy_rng");
224