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