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 - 2023
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 <crypto/hash.h>
41 #include <crypto/sha3.h>
42 #include <linux/fips.h>
43 #include <linux/kernel.h>
44 #include <linux/module.h>
45 #include <linux/slab.h>
46 #include <linux/time.h>
47 #include <crypto/internal/rng.h>
48
49 #include "jitterentropy.h"
50
51 #define JENT_CONDITIONING_HASH "sha3-256-generic"
52
53 /***************************************************************************
54 * Helper function
55 ***************************************************************************/
56
jent_zalloc(unsigned int len)57 void *jent_zalloc(unsigned int len)
58 {
59 return kzalloc(len, GFP_KERNEL);
60 }
61
jent_zfree(void * ptr)62 void jent_zfree(void *ptr)
63 {
64 kfree_sensitive(ptr);
65 }
66
67 /*
68 * Obtain a high-resolution time stamp value. The time stamp is used to measure
69 * the execution time of a given code path and its variations. Hence, the time
70 * stamp must have a sufficiently high resolution.
71 *
72 * Note, if the function returns zero because a given architecture does not
73 * implement a high-resolution time stamp, the RNG code's runtime test
74 * will detect it and will not produce output.
75 */
jent_get_nstime(__u64 * out)76 void jent_get_nstime(__u64 *out)
77 {
78 __u64 tmp = 0;
79
80 tmp = random_get_entropy();
81
82 /*
83 * If random_get_entropy does not return a value, i.e. it is not
84 * implemented for a given architecture, use a clock source.
85 * hoping that there are timers we can work with.
86 */
87 if (tmp == 0)
88 tmp = ktime_get_ns();
89
90 *out = tmp;
91 jent_raw_hires_entropy_store(tmp);
92 }
93
jent_hash_time(void * hash_state,__u64 time,u8 * addtl,unsigned int addtl_len,__u64 hash_loop_cnt,unsigned int stuck)94 int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
95 unsigned int addtl_len, __u64 hash_loop_cnt,
96 unsigned int stuck)
97 {
98 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
99 SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm);
100 u8 intermediary[SHA3_256_DIGEST_SIZE];
101 __u64 j = 0;
102 int ret;
103
104 desc->tfm = hash_state_desc->tfm;
105
106 if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) {
107 pr_warn_ratelimited("Unexpected digest size\n");
108 return -EINVAL;
109 }
110
111 /*
112 * This loop fills a buffer which is injected into the entropy pool.
113 * The main reason for this loop is to execute something over which we
114 * can perform a timing measurement. The injection of the resulting
115 * data into the pool is performed to ensure the result is used and
116 * the compiler cannot optimize the loop away in case the result is not
117 * used at all. Yet that data is considered "additional information"
118 * considering the terminology from SP800-90A without any entropy.
119 *
120 * Note, it does not matter which or how much data you inject, we are
121 * interested in one Keccack1600 compression operation performed with
122 * the crypto_shash_final.
123 */
124 for (j = 0; j < hash_loop_cnt; j++) {
125 ret = crypto_shash_init(desc) ?:
126 crypto_shash_update(desc, intermediary,
127 sizeof(intermediary)) ?:
128 crypto_shash_finup(desc, addtl, addtl_len, intermediary);
129 if (ret)
130 goto err;
131 }
132
133 /*
134 * Inject the data from the previous loop into the pool. This data is
135 * not considered to contain any entropy, but it stirs the pool a bit.
136 */
137 ret = crypto_shash_update(desc, intermediary, sizeof(intermediary));
138 if (ret)
139 goto err;
140
141 /*
142 * Insert the time stamp into the hash context representing the pool.
143 *
144 * If the time stamp is stuck, do not finally insert the value into the
145 * entropy pool. Although this operation should not do any harm even
146 * when the time stamp has no entropy, SP800-90B requires that any
147 * conditioning operation to have an identical amount of input data
148 * according to section 3.1.5.
149 */
150 if (!stuck) {
151 ret = crypto_shash_update(hash_state_desc, (u8 *)&time,
152 sizeof(__u64));
153 }
154
155 err:
156 shash_desc_zero(desc);
157 memzero_explicit(intermediary, sizeof(intermediary));
158
159 return ret;
160 }
161
jent_read_random_block(void * hash_state,char * dst,unsigned int dst_len)162 int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len)
163 {
164 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
165 u8 jent_block[SHA3_256_DIGEST_SIZE];
166 /* Obtain data from entropy pool and re-initialize it */
167 int ret = crypto_shash_final(hash_state_desc, jent_block) ?:
168 crypto_shash_init(hash_state_desc) ?:
169 crypto_shash_update(hash_state_desc, jent_block,
170 sizeof(jent_block));
171
172 if (!ret && dst_len)
173 memcpy(dst, jent_block, dst_len);
174
175 memzero_explicit(jent_block, sizeof(jent_block));
176 return ret;
177 }
178
179 /***************************************************************************
180 * Kernel crypto API interface
181 ***************************************************************************/
182
183 struct jitterentropy {
184 spinlock_t jent_lock;
185 struct rand_data *entropy_collector;
186 struct crypto_shash *tfm;
187 struct shash_desc *sdesc;
188 };
189
jent_kcapi_cleanup(struct crypto_tfm * tfm)190 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
191 {
192 struct jitterentropy *rng = crypto_tfm_ctx(tfm);
193
194 spin_lock(&rng->jent_lock);
195
196 if (rng->sdesc) {
197 shash_desc_zero(rng->sdesc);
198 kfree(rng->sdesc);
199 }
200 rng->sdesc = NULL;
201
202 if (rng->tfm)
203 crypto_free_shash(rng->tfm);
204 rng->tfm = NULL;
205
206 if (rng->entropy_collector)
207 jent_entropy_collector_free(rng->entropy_collector);
208 rng->entropy_collector = NULL;
209 spin_unlock(&rng->jent_lock);
210 }
211
jent_kcapi_init(struct crypto_tfm * tfm)212 static int jent_kcapi_init(struct crypto_tfm *tfm)
213 {
214 struct jitterentropy *rng = crypto_tfm_ctx(tfm);
215 struct crypto_shash *hash;
216 struct shash_desc *sdesc;
217 int size, ret = 0;
218
219 spin_lock_init(&rng->jent_lock);
220
221 /*
222 * Use SHA3-256 as conditioner. We allocate only the generic
223 * implementation as we are not interested in high-performance. The
224 * execution time of the SHA3 operation is measured and adds to the
225 * Jitter RNG's unpredictable behavior. If we have a slower hash
226 * implementation, the execution timing variations are larger. When
227 * using a fast implementation, we would need to call it more often
228 * as its variations are lower.
229 */
230 hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
231 if (IS_ERR(hash)) {
232 pr_err("Cannot allocate conditioning digest\n");
233 return PTR_ERR(hash);
234 }
235 rng->tfm = hash;
236
237 size = sizeof(struct shash_desc) + crypto_shash_descsize(hash);
238 sdesc = kmalloc(size, GFP_KERNEL);
239 if (!sdesc) {
240 ret = -ENOMEM;
241 goto err;
242 }
243
244 sdesc->tfm = hash;
245 crypto_shash_init(sdesc);
246 rng->sdesc = sdesc;
247
248 rng->entropy_collector = jent_entropy_collector_alloc(1, 0, sdesc);
249 if (!rng->entropy_collector) {
250 ret = -ENOMEM;
251 goto err;
252 }
253
254 spin_lock_init(&rng->jent_lock);
255 return 0;
256
257 err:
258 jent_kcapi_cleanup(tfm);
259 return ret;
260 }
261
jent_kcapi_random(struct crypto_rng * tfm,const u8 * src,unsigned int slen,u8 * rdata,unsigned int dlen)262 static int jent_kcapi_random(struct crypto_rng *tfm,
263 const u8 *src, unsigned int slen,
264 u8 *rdata, unsigned int dlen)
265 {
266 struct jitterentropy *rng = crypto_rng_ctx(tfm);
267 int ret = 0;
268
269 spin_lock(&rng->jent_lock);
270
271 ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
272
273 if (ret == -3) {
274 /* Handle permanent health test error */
275 /*
276 * If the kernel was booted with fips=1, it implies that
277 * the entire kernel acts as a FIPS 140 module. In this case
278 * an SP800-90B permanent health test error is treated as
279 * a FIPS module error.
280 */
281 if (fips_enabled)
282 panic("Jitter RNG permanent health test failure\n");
283
284 pr_err("Jitter RNG permanent health test failure\n");
285 ret = -EFAULT;
286 } else if (ret == -2) {
287 /* Handle intermittent health test error */
288 pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n");
289 ret = -EAGAIN;
290 } else if (ret == -1) {
291 /* Handle other errors */
292 ret = -EINVAL;
293 }
294
295 spin_unlock(&rng->jent_lock);
296
297 return ret;
298 }
299
jent_kcapi_reset(struct crypto_rng * tfm,const u8 * seed,unsigned int slen)300 static int jent_kcapi_reset(struct crypto_rng *tfm,
301 const u8 *seed, unsigned int slen)
302 {
303 return 0;
304 }
305
306 static struct rng_alg jent_alg = {
307 .generate = jent_kcapi_random,
308 .seed = jent_kcapi_reset,
309 .seedsize = 0,
310 .base = {
311 .cra_name = "jitterentropy_rng",
312 .cra_driver_name = "jitterentropy_rng",
313 .cra_priority = 100,
314 .cra_ctxsize = sizeof(struct jitterentropy),
315 .cra_module = THIS_MODULE,
316 .cra_init = jent_kcapi_init,
317 .cra_exit = jent_kcapi_cleanup,
318 }
319 };
320
jent_mod_init(void)321 static int __init jent_mod_init(void)
322 {
323 SHASH_DESC_ON_STACK(desc, tfm);
324 struct crypto_shash *tfm;
325 int ret = 0;
326
327 jent_testing_init();
328
329 tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
330 if (IS_ERR(tfm)) {
331 jent_testing_exit();
332 return PTR_ERR(tfm);
333 }
334
335 desc->tfm = tfm;
336 crypto_shash_init(desc);
337 ret = jent_entropy_init(desc);
338 shash_desc_zero(desc);
339 crypto_free_shash(tfm);
340 if (ret) {
341 /* Handle permanent health test error */
342 if (fips_enabled)
343 panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
344
345 jent_testing_exit();
346 pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
347 return -EFAULT;
348 }
349 return crypto_register_rng(&jent_alg);
350 }
351
jent_mod_exit(void)352 static void __exit jent_mod_exit(void)
353 {
354 jent_testing_exit();
355 crypto_unregister_rng(&jent_alg);
356 }
357
358 module_init(jent_mod_init);
359 module_exit(jent_mod_exit);
360
361 MODULE_LICENSE("Dual BSD/GPL");
362 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
363 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
364 MODULE_ALIAS_CRYPTO("jitterentropy_rng");
365
