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 57 void *jent_kvzalloc(unsigned int len) 58 { 59 return kvzalloc(len, GFP_KERNEL); 60 } 61 62 void jent_kvzfree(void *ptr, unsigned int len) 63 { 64 memzero_explicit(ptr, len); 65 kvfree(ptr); 66 } 67 68 void *jent_zalloc(unsigned int len) 69 { 70 return kzalloc(len, GFP_KERNEL); 71 } 72 73 void jent_zfree(void *ptr) 74 { 75 kfree_sensitive(ptr); 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 */ 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 jent_raw_hires_entropy_store(tmp); 103 } 104 105 int jent_hash_time(void *hash_state, __u64 time, u8 *addtl, 106 unsigned int addtl_len, __u64 hash_loop_cnt, 107 unsigned int stuck) 108 { 109 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state; 110 SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm); 111 u8 intermediary[SHA3_256_DIGEST_SIZE]; 112 __u64 j = 0; 113 int ret; 114 115 desc->tfm = hash_state_desc->tfm; 116 117 if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) { 118 pr_warn_ratelimited("Unexpected digest size\n"); 119 return -EINVAL; 120 } 121 122 /* 123 * This loop fills a buffer which is injected into the entropy pool. 124 * The main reason for this loop is to execute something over which we 125 * can perform a timing measurement. The injection of the resulting 126 * data into the pool is performed to ensure the result is used and 127 * the compiler cannot optimize the loop away in case the result is not 128 * used at all. Yet that data is considered "additional information" 129 * considering the terminology from SP800-90A without any entropy. 130 * 131 * Note, it does not matter which or how much data you inject, we are 132 * interested in one Keccack1600 compression operation performed with 133 * the crypto_shash_final. 134 */ 135 for (j = 0; j < hash_loop_cnt; j++) { 136 ret = crypto_shash_init(desc) ?: 137 crypto_shash_update(desc, intermediary, 138 sizeof(intermediary)) ?: 139 crypto_shash_finup(desc, addtl, addtl_len, intermediary); 140 if (ret) 141 goto err; 142 } 143 144 /* 145 * Inject the data from the previous loop into the pool. This data is 146 * not considered to contain any entropy, but it stirs the pool a bit. 147 */ 148 ret = crypto_shash_update(desc, intermediary, sizeof(intermediary)); 149 if (ret) 150 goto err; 151 152 /* 153 * Insert the time stamp into the hash context representing the pool. 154 * 155 * If the time stamp is stuck, do not finally insert the value into the 156 * entropy pool. Although this operation should not do any harm even 157 * when the time stamp has no entropy, SP800-90B requires that any 158 * conditioning operation to have an identical amount of input data 159 * according to section 3.1.5. 160 */ 161 if (!stuck) { 162 ret = crypto_shash_update(hash_state_desc, (u8 *)&time, 163 sizeof(__u64)); 164 } 165 166 err: 167 shash_desc_zero(desc); 168 memzero_explicit(intermediary, sizeof(intermediary)); 169 170 return ret; 171 } 172 173 int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len) 174 { 175 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state; 176 u8 jent_block[SHA3_256_DIGEST_SIZE]; 177 /* Obtain data from entropy pool and re-initialize it */ 178 int ret = crypto_shash_final(hash_state_desc, jent_block) ?: 179 crypto_shash_init(hash_state_desc) ?: 180 crypto_shash_update(hash_state_desc, jent_block, 181 sizeof(jent_block)); 182 183 if (!ret && dst_len) 184 memcpy(dst, jent_block, dst_len); 185 186 memzero_explicit(jent_block, sizeof(jent_block)); 187 return ret; 188 } 189 190 /*************************************************************************** 191 * Kernel crypto API interface 192 ***************************************************************************/ 193 194 struct jitterentropy { 195 spinlock_t jent_lock; 196 struct rand_data *entropy_collector; 197 struct crypto_shash *tfm; 198 struct shash_desc *sdesc; 199 }; 200 201 static void jent_kcapi_cleanup(struct crypto_tfm *tfm) 202 { 203 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 204 205 spin_lock(&rng->jent_lock); 206 207 if (rng->sdesc) { 208 shash_desc_zero(rng->sdesc); 209 kfree(rng->sdesc); 210 } 211 rng->sdesc = NULL; 212 213 if (rng->tfm) 214 crypto_free_shash(rng->tfm); 215 rng->tfm = NULL; 216 217 if (rng->entropy_collector) 218 jent_entropy_collector_free(rng->entropy_collector); 219 rng->entropy_collector = NULL; 220 spin_unlock(&rng->jent_lock); 221 } 222 223 static int jent_kcapi_init(struct crypto_tfm *tfm) 224 { 225 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 226 struct crypto_shash *hash; 227 struct shash_desc *sdesc; 228 int size, ret = 0; 229 230 spin_lock_init(&rng->jent_lock); 231 232 /* 233 * Use SHA3-256 as conditioner. We allocate only the generic 234 * implementation as we are not interested in high-performance. The 235 * execution time of the SHA3 operation is measured and adds to the 236 * Jitter RNG's unpredictable behavior. If we have a slower hash 237 * implementation, the execution timing variations are larger. When 238 * using a fast implementation, we would need to call it more often 239 * as its variations are lower. 240 */ 241 hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0); 242 if (IS_ERR(hash)) { 243 pr_err("Cannot allocate conditioning digest\n"); 244 return PTR_ERR(hash); 245 } 246 rng->tfm = hash; 247 248 size = sizeof(struct shash_desc) + crypto_shash_descsize(hash); 249 sdesc = kmalloc(size, GFP_KERNEL); 250 if (!sdesc) { 251 ret = -ENOMEM; 252 goto err; 253 } 254 255 sdesc->tfm = hash; 256 crypto_shash_init(sdesc); 257 rng->sdesc = sdesc; 258 259 rng->entropy_collector = 260 jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, 261 sdesc); 262 if (!rng->entropy_collector) { 263 ret = -ENOMEM; 264 goto err; 265 } 266 267 spin_lock_init(&rng->jent_lock); 268 return 0; 269 270 err: 271 jent_kcapi_cleanup(tfm); 272 return ret; 273 } 274 275 static int jent_kcapi_random(struct crypto_rng *tfm, 276 const u8 *src, unsigned int slen, 277 u8 *rdata, unsigned int dlen) 278 { 279 struct jitterentropy *rng = crypto_rng_ctx(tfm); 280 int ret = 0; 281 282 spin_lock(&rng->jent_lock); 283 284 ret = jent_read_entropy(rng->entropy_collector, rdata, dlen); 285 286 if (ret == -3) { 287 /* Handle permanent health test error */ 288 /* 289 * If the kernel was booted with fips=1, it implies that 290 * the entire kernel acts as a FIPS 140 module. In this case 291 * an SP800-90B permanent health test error is treated as 292 * a FIPS module error. 293 */ 294 if (fips_enabled) 295 panic("Jitter RNG permanent health test failure\n"); 296 297 pr_err("Jitter RNG permanent health test failure\n"); 298 ret = -EFAULT; 299 } else if (ret == -2) { 300 /* Handle intermittent health test error */ 301 pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n"); 302 ret = -EAGAIN; 303 } else if (ret == -1) { 304 /* Handle other errors */ 305 ret = -EINVAL; 306 } 307 308 spin_unlock(&rng->jent_lock); 309 310 return ret; 311 } 312 313 static int jent_kcapi_reset(struct crypto_rng *tfm, 314 const u8 *seed, unsigned int slen) 315 { 316 return 0; 317 } 318 319 static struct rng_alg jent_alg = { 320 .generate = jent_kcapi_random, 321 .seed = jent_kcapi_reset, 322 .seedsize = 0, 323 .base = { 324 .cra_name = "jitterentropy_rng", 325 .cra_driver_name = "jitterentropy_rng", 326 .cra_priority = 100, 327 .cra_ctxsize = sizeof(struct jitterentropy), 328 .cra_module = THIS_MODULE, 329 .cra_init = jent_kcapi_init, 330 .cra_exit = jent_kcapi_cleanup, 331 } 332 }; 333 334 static int __init jent_mod_init(void) 335 { 336 SHASH_DESC_ON_STACK(desc, tfm); 337 struct crypto_shash *tfm; 338 int ret = 0; 339 340 jent_testing_init(); 341 342 tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0); 343 if (IS_ERR(tfm)) { 344 jent_testing_exit(); 345 return PTR_ERR(tfm); 346 } 347 348 desc->tfm = tfm; 349 crypto_shash_init(desc); 350 ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc, NULL); 351 shash_desc_zero(desc); 352 crypto_free_shash(tfm); 353 if (ret) { 354 /* Handle permanent health test error */ 355 if (fips_enabled) 356 panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); 357 358 jent_testing_exit(); 359 pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); 360 return -EFAULT; 361 } 362 return crypto_register_rng(&jent_alg); 363 } 364 365 static void __exit jent_mod_exit(void) 366 { 367 jent_testing_exit(); 368 crypto_unregister_rng(&jent_alg); 369 } 370 371 module_init(jent_mod_init); 372 module_exit(jent_mod_exit); 373 374 MODULE_LICENSE("Dual BSD/GPL"); 375 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 376 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter"); 377 MODULE_ALIAS_CRYPTO("jitterentropy_rng"); 378