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 kvfree_sensitive(ptr, len); 65 } 66 67 void *jent_zalloc(unsigned int len) 68 { 69 return kzalloc(len, GFP_KERNEL); 70 } 71 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 */ 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 } 103 104 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 } 171 172 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 }; 199 200 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 } 221 222 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 } 273 274 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 } 311 312 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 }; 332 333 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 } 363 364 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