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/kernel.h>
41 #include <linux/module.h>
42 #include <linux/slab.h>
43 #include <linux/time.h>
44 #include <crypto/internal/rng.h>
45 
46 #include "jitterentropy.h"
47 
48 /***************************************************************************
49  * Helper function
50  ***************************************************************************/
51 
jent_zalloc(unsigned int len)52 void *jent_zalloc(unsigned int len)
53 {
54 	return kzalloc(len, GFP_KERNEL);
55 }
56 
jent_zfree(void * ptr)57 void jent_zfree(void *ptr)
58 {
59 	kfree_sensitive(ptr);
60 }
61 
jent_panic(char * s)62 void jent_panic(char *s)
63 {
64 	panic("%s", s);
65 }
66 
jent_memcpy(void * dest,const void * src,unsigned int n)67 void jent_memcpy(void *dest, const void *src, unsigned int n)
68 {
69 	memcpy(dest, src, n);
70 }
71 
72 /*
73  * Obtain a high-resolution time stamp value. The time stamp is used to measure
74  * the execution time of a given code path and its variations. Hence, the time
75  * stamp must have a sufficiently high resolution.
76  *
77  * Note, if the function returns zero because a given architecture does not
78  * implement a high-resolution time stamp, the RNG code's runtime test
79  * will detect it and will not produce output.
80  */
jent_get_nstime(__u64 * out)81 void jent_get_nstime(__u64 *out)
82 {
83 	__u64 tmp = 0;
84 
85 	tmp = random_get_entropy();
86 
87 	/*
88 	 * If random_get_entropy does not return a value, i.e. it is not
89 	 * implemented for a given architecture, use a clock source.
90 	 * hoping that there are timers we can work with.
91 	 */
92 	if (tmp == 0)
93 		tmp = ktime_get_ns();
94 
95 	*out = tmp;
96 }
97 
98 /***************************************************************************
99  * Kernel crypto API interface
100  ***************************************************************************/
101 
102 struct jitterentropy {
103 	spinlock_t jent_lock;
104 	struct rand_data *entropy_collector;
105 	unsigned int reset_cnt;
106 };
107 
jent_kcapi_init(struct crypto_tfm * tfm)108 static int jent_kcapi_init(struct crypto_tfm *tfm)
109 {
110 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
111 	int ret = 0;
112 
113 	rng->entropy_collector = jent_entropy_collector_alloc(1, 0);
114 	if (!rng->entropy_collector)
115 		ret = -ENOMEM;
116 
117 	spin_lock_init(&rng->jent_lock);
118 	return ret;
119 }
120 
jent_kcapi_cleanup(struct crypto_tfm * tfm)121 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
122 {
123 	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
124 
125 	spin_lock(&rng->jent_lock);
126 	if (rng->entropy_collector)
127 		jent_entropy_collector_free(rng->entropy_collector);
128 	rng->entropy_collector = NULL;
129 	spin_unlock(&rng->jent_lock);
130 }
131 
jent_kcapi_random(struct crypto_rng * tfm,const u8 * src,unsigned int slen,u8 * rdata,unsigned int dlen)132 static int jent_kcapi_random(struct crypto_rng *tfm,
133 			     const u8 *src, unsigned int slen,
134 			     u8 *rdata, unsigned int dlen)
135 {
136 	struct jitterentropy *rng = crypto_rng_ctx(tfm);
137 	int ret = 0;
138 
139 	spin_lock(&rng->jent_lock);
140 
141 	/* Return a permanent error in case we had too many resets in a row. */
142 	if (rng->reset_cnt > (1<<10)) {
143 		ret = -EFAULT;
144 		goto out;
145 	}
146 
147 	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
148 
149 	/* Reset RNG in case of health failures */
150 	if (ret < -1) {
151 		pr_warn_ratelimited("Reset Jitter RNG due to health test failure: %s failure\n",
152 				    (ret == -2) ? "Repetition Count Test" :
153 						  "Adaptive Proportion Test");
154 
155 		rng->reset_cnt++;
156 
157 		ret = -EAGAIN;
158 	} else {
159 		rng->reset_cnt = 0;
160 
161 		/* Convert the Jitter RNG error into a usable error code */
162 		if (ret == -1)
163 			ret = -EINVAL;
164 	}
165 
166 out:
167 	spin_unlock(&rng->jent_lock);
168 
169 	return ret;
170 }
171 
jent_kcapi_reset(struct crypto_rng * tfm,const u8 * seed,unsigned int slen)172 static int jent_kcapi_reset(struct crypto_rng *tfm,
173 			    const u8 *seed, unsigned int slen)
174 {
175 	return 0;
176 }
177 
178 static struct rng_alg jent_alg = {
179 	.generate		= jent_kcapi_random,
180 	.seed			= jent_kcapi_reset,
181 	.seedsize		= 0,
182 	.base			= {
183 		.cra_name               = "jitterentropy_rng",
184 		.cra_driver_name        = "jitterentropy_rng",
185 		.cra_priority           = 100,
186 		.cra_ctxsize            = sizeof(struct jitterentropy),
187 		.cra_module             = THIS_MODULE,
188 		.cra_init               = jent_kcapi_init,
189 		.cra_exit               = jent_kcapi_cleanup,
190 
191 	}
192 };
193 
jent_mod_init(void)194 static int __init jent_mod_init(void)
195 {
196 	int ret = 0;
197 
198 	ret = jent_entropy_init();
199 	if (ret) {
200 		pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
201 		return -EFAULT;
202 	}
203 	return crypto_register_rng(&jent_alg);
204 }
205 
jent_mod_exit(void)206 static void __exit jent_mod_exit(void)
207 {
208 	crypto_unregister_rng(&jent_alg);
209 }
210 
211 module_init(jent_mod_init);
212 module_exit(jent_mod_exit);
213 
214 MODULE_LICENSE("Dual BSD/GPL");
215 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
216 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
217 MODULE_ALIAS_CRYPTO("jitterentropy_rng");
218