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_kvzalloc(unsigned int len)57 void *jent_kvzalloc(unsigned int len)
58 {
59 return kvzalloc(len, GFP_KERNEL);
60 }
61
jent_kvzfree(void * ptr,unsigned int len)62 void jent_kvzfree(void *ptr, unsigned int len)
63 {
64 kvfree_sensitive(ptr, len);
65 }
66
jent_zalloc(unsigned int len)67 void *jent_zalloc(unsigned int len)
68 {
69 return kzalloc(len, GFP_KERNEL);
70 }
71
jent_zfree(void * ptr)72 void jent_zfree(void *ptr)
73 {
74 kfree_sensitive(ptr);
75 }
76
77 /*
78 * Obtain a high-resolution time stamp value. The time stamp is used to measure
79 * the execution time of a given code path and its variations. Hence, the time
80 * stamp must have a sufficiently high resolution.
81 *
82 * Note, if the function returns zero because a given architecture does not
83 * implement a high-resolution time stamp, the RNG code's runtime test
84 * will detect it and will not produce output.
85 */
jent_get_nstime(__u64 * out)86 void jent_get_nstime(__u64 *out)
87 {
88 __u64 tmp = 0;
89
90 tmp = random_get_entropy();
91
92 /*
93 * If random_get_entropy does not return a value, i.e. it is not
94 * implemented for a given architecture, use a clock source.
95 * hoping that there are timers we can work with.
96 */
97 if (tmp == 0)
98 tmp = ktime_get_ns();
99
100 *out = tmp;
101 jent_raw_hires_entropy_store(tmp);
102 }
103
jent_hash_time(void * hash_state,__u64 time,u8 * addtl,unsigned int addtl_len,__u64 hash_loop_cnt,unsigned int stuck)104 int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
105 unsigned int addtl_len, __u64 hash_loop_cnt,
106 unsigned int stuck)
107 {
108 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
109 SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm);
110 u8 intermediary[SHA3_256_DIGEST_SIZE];
111 __u64 j = 0;
112 int ret;
113
114 desc->tfm = hash_state_desc->tfm;
115
116 if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) {
117 pr_warn_ratelimited("Unexpected digest size\n");
118 return -EINVAL;
119 }
120
121 /*
122 * This loop fills a buffer which is injected into the entropy pool.
123 * The main reason for this loop is to execute something over which we
124 * can perform a timing measurement. The injection of the resulting
125 * data into the pool is performed to ensure the result is used and
126 * the compiler cannot optimize the loop away in case the result is not
127 * used at all. Yet that data is considered "additional information"
128 * considering the terminology from SP800-90A without any entropy.
129 *
130 * Note, it does not matter which or how much data you inject, we are
131 * interested in one Keccack1600 compression operation performed with
132 * the crypto_shash_final.
133 */
134 for (j = 0; j < hash_loop_cnt; j++) {
135 ret = crypto_shash_init(desc) ?:
136 crypto_shash_update(desc, intermediary,
137 sizeof(intermediary)) ?:
138 crypto_shash_finup(desc, addtl, addtl_len, intermediary);
139 if (ret)
140 goto err;
141 }
142
143 /*
144 * Inject the data from the previous loop into the pool. This data is
145 * not considered to contain any entropy, but it stirs the pool a bit.
146 */
147 ret = crypto_shash_update(desc, intermediary, sizeof(intermediary));
148 if (ret)
149 goto err;
150
151 /*
152 * Insert the time stamp into the hash context representing the pool.
153 *
154 * If the time stamp is stuck, do not finally insert the value into the
155 * entropy pool. Although this operation should not do any harm even
156 * when the time stamp has no entropy, SP800-90B requires that any
157 * conditioning operation to have an identical amount of input data
158 * according to section 3.1.5.
159 */
160 if (!stuck) {
161 ret = crypto_shash_update(hash_state_desc, (u8 *)&time,
162 sizeof(__u64));
163 }
164
165 err:
166 shash_desc_zero(desc);
167 memzero_explicit(intermediary, sizeof(intermediary));
168
169 return ret;
170 }
171
jent_read_random_block(void * hash_state,char * dst,unsigned int dst_len)172 int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len)
173 {
174 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
175 u8 jent_block[SHA3_256_DIGEST_SIZE];
176 /* Obtain data from entropy pool and re-initialize it */
177 int ret = crypto_shash_final(hash_state_desc, jent_block) ?:
178 crypto_shash_init(hash_state_desc) ?:
179 crypto_shash_update(hash_state_desc, jent_block,
180 sizeof(jent_block));
181
182 if (!ret && dst_len)
183 memcpy(dst, jent_block, dst_len);
184
185 memzero_explicit(jent_block, sizeof(jent_block));
186 return ret;
187 }
188
189 /***************************************************************************
190 * Kernel crypto API interface
191 ***************************************************************************/
192
193 struct jitterentropy {
194 spinlock_t jent_lock;
195 struct rand_data *entropy_collector;
196 struct crypto_shash *tfm;
197 struct shash_desc *sdesc;
198 };
199
jent_kcapi_cleanup(struct crypto_tfm * tfm)200 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
201 {
202 struct jitterentropy *rng = crypto_tfm_ctx(tfm);
203
204 spin_lock(&rng->jent_lock);
205
206 if (rng->sdesc) {
207 shash_desc_zero(rng->sdesc);
208 kfree(rng->sdesc);
209 }
210 rng->sdesc = NULL;
211
212 if (rng->tfm)
213 crypto_free_shash(rng->tfm);
214 rng->tfm = NULL;
215
216 if (rng->entropy_collector)
217 jent_entropy_collector_free(rng->entropy_collector);
218 rng->entropy_collector = NULL;
219 spin_unlock(&rng->jent_lock);
220 }
221
jent_kcapi_init(struct crypto_tfm * tfm)222 static int jent_kcapi_init(struct crypto_tfm *tfm)
223 {
224 struct jitterentropy *rng = crypto_tfm_ctx(tfm);
225 struct crypto_shash *hash;
226 struct shash_desc *sdesc;
227 int size, ret = 0;
228
229 spin_lock_init(&rng->jent_lock);
230
231 /*
232 * Use SHA3-256 as conditioner. We allocate only the generic
233 * implementation as we are not interested in high-performance. The
234 * execution time of the SHA3 operation is measured and adds to the
235 * Jitter RNG's unpredictable behavior. If we have a slower hash
236 * implementation, the execution timing variations are larger. When
237 * using a fast implementation, we would need to call it more often
238 * as its variations are lower.
239 */
240 hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
241 if (IS_ERR(hash)) {
242 pr_err("Cannot allocate conditioning digest\n");
243 return PTR_ERR(hash);
244 }
245 rng->tfm = hash;
246
247 size = sizeof(struct shash_desc) + crypto_shash_descsize(hash);
248 sdesc = kmalloc(size, GFP_KERNEL);
249 if (!sdesc) {
250 ret = -ENOMEM;
251 goto err;
252 }
253
254 sdesc->tfm = hash;
255 crypto_shash_init(sdesc);
256 rng->sdesc = sdesc;
257
258 rng->entropy_collector =
259 jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0,
260 sdesc);
261 if (!rng->entropy_collector) {
262 ret = -ENOMEM;
263 goto err;
264 }
265
266 spin_lock_init(&rng->jent_lock);
267 return 0;
268
269 err:
270 jent_kcapi_cleanup(tfm);
271 return ret;
272 }
273
jent_kcapi_random(struct crypto_rng * tfm,const u8 * src,unsigned int slen,u8 * rdata,unsigned int dlen)274 static int jent_kcapi_random(struct crypto_rng *tfm,
275 const u8 *src, unsigned int slen,
276 u8 *rdata, unsigned int dlen)
277 {
278 struct jitterentropy *rng = crypto_rng_ctx(tfm);
279 int ret = 0;
280
281 spin_lock(&rng->jent_lock);
282
283 ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
284
285 if (ret == -3) {
286 /* Handle permanent health test error */
287 /*
288 * If the kernel was booted with fips=1, it implies that
289 * the entire kernel acts as a FIPS 140 module. In this case
290 * an SP800-90B permanent health test error is treated as
291 * a FIPS module error.
292 */
293 if (fips_enabled)
294 panic("Jitter RNG permanent health test failure\n");
295
296 pr_err("Jitter RNG permanent health test failure\n");
297 ret = -EFAULT;
298 } else if (ret == -2) {
299 /* Handle intermittent health test error */
300 pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n");
301 ret = -EAGAIN;
302 } else if (ret == -1) {
303 /* Handle other errors */
304 ret = -EINVAL;
305 }
306
307 spin_unlock(&rng->jent_lock);
308
309 return ret;
310 }
311
jent_kcapi_reset(struct crypto_rng * tfm,const u8 * seed,unsigned int slen)312 static int jent_kcapi_reset(struct crypto_rng *tfm,
313 const u8 *seed, unsigned int slen)
314 {
315 return 0;
316 }
317
318 static struct rng_alg jent_alg = {
319 .generate = jent_kcapi_random,
320 .seed = jent_kcapi_reset,
321 .seedsize = 0,
322 .base = {
323 .cra_name = "jitterentropy_rng",
324 .cra_driver_name = "jitterentropy_rng",
325 .cra_priority = 100,
326 .cra_ctxsize = sizeof(struct jitterentropy),
327 .cra_module = THIS_MODULE,
328 .cra_init = jent_kcapi_init,
329 .cra_exit = jent_kcapi_cleanup,
330 }
331 };
332
jent_mod_init(void)333 static int __init jent_mod_init(void)
334 {
335 SHASH_DESC_ON_STACK(desc, tfm);
336 struct crypto_shash *tfm;
337 int ret = 0;
338
339 jent_testing_init();
340
341 tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
342 if (IS_ERR(tfm)) {
343 jent_testing_exit();
344 return PTR_ERR(tfm);
345 }
346
347 desc->tfm = tfm;
348 crypto_shash_init(desc);
349 ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc, NULL);
350 shash_desc_zero(desc);
351 crypto_free_shash(tfm);
352 if (ret) {
353 /* Handle permanent health test error */
354 if (fips_enabled)
355 panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
356
357 jent_testing_exit();
358 pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
359 return -EFAULT;
360 }
361 return crypto_register_rng(&jent_alg);
362 }
363
jent_mod_exit(void)364 static void __exit jent_mod_exit(void)
365 {
366 jent_testing_exit();
367 crypto_unregister_rng(&jent_alg);
368 }
369
370 module_init(jent_mod_init);
371 module_exit(jent_mod_exit);
372
373 MODULE_LICENSE("Dual BSD/GPL");
374 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
375 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
376 MODULE_ALIAS_CRYPTO("jitterentropy_rng");
377