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/fips.h>
44 #include <linux/time.h>
45 #include <crypto/internal/rng.h>
46
47 #include "jitterentropy.h"
48
49 /***************************************************************************
50 * Helper function
51 ***************************************************************************/
52
jent_zalloc(unsigned int len)53 void *jent_zalloc(unsigned int len)
54 {
55 return kzalloc(len, GFP_KERNEL);
56 }
57
jent_zfree(void * ptr)58 void jent_zfree(void *ptr)
59 {
60 kfree_sensitive(ptr);
61 }
62
jent_fips_enabled(void)63 int jent_fips_enabled(void)
64 {
65 return fips_enabled;
66 }
67
jent_panic(char * s)68 void jent_panic(char *s)
69 {
70 panic("%s", s);
71 }
72
jent_memcpy(void * dest,const void * src,unsigned int n)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 */
jent_get_nstime(__u64 * out)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
jent_kcapi_init(struct crypto_tfm * tfm)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
jent_kcapi_cleanup(struct crypto_tfm * tfm)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
jent_kcapi_random(struct crypto_rng * tfm,const u8 * src,unsigned int slen,u8 * rdata,unsigned int dlen)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
jent_kcapi_reset(struct crypto_rng * tfm,const u8 * seed,unsigned int slen)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
jent_mod_init(void)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
jent_mod_exit(void)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