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" 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 kmsan_unpoison_memory(intermediary, sizeof(intermediary)); 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(hash_state_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 time = 0; 163 } 164 165 ret = crypto_shash_update(hash_state_desc, (u8 *)&time, sizeof(__u64)); 166 167 err: 168 shash_desc_zero(desc); 169 memzero_explicit(intermediary, sizeof(intermediary)); 170 171 return ret; 172 } 173 174 int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len) 175 { 176 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state; 177 u8 jent_block[SHA3_256_DIGEST_SIZE]; 178 /* Obtain data from entropy pool and re-initialize it */ 179 int ret = crypto_shash_final(hash_state_desc, jent_block) ?: 180 crypto_shash_init(hash_state_desc) ?: 181 crypto_shash_update(hash_state_desc, jent_block, 182 sizeof(jent_block)); 183 184 if (!ret && dst_len) 185 memcpy(dst, jent_block, dst_len); 186 187 memzero_explicit(jent_block, sizeof(jent_block)); 188 return ret; 189 } 190 191 /*************************************************************************** 192 * Kernel crypto API interface 193 ***************************************************************************/ 194 195 struct jitterentropy { 196 spinlock_t jent_lock; 197 struct rand_data *entropy_collector; 198 struct crypto_shash *tfm; 199 struct shash_desc *sdesc; 200 }; 201 202 static void jent_kcapi_cleanup(struct crypto_tfm *tfm) 203 { 204 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 205 206 spin_lock(&rng->jent_lock); 207 208 if (rng->sdesc) { 209 shash_desc_zero(rng->sdesc); 210 kfree(rng->sdesc); 211 } 212 rng->sdesc = NULL; 213 214 if (rng->tfm) 215 crypto_free_shash(rng->tfm); 216 rng->tfm = NULL; 217 218 if (rng->entropy_collector) 219 jent_entropy_collector_free(rng->entropy_collector); 220 rng->entropy_collector = NULL; 221 spin_unlock(&rng->jent_lock); 222 } 223 224 static int jent_kcapi_init(struct crypto_tfm *tfm) 225 { 226 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 227 struct crypto_shash *hash; 228 struct shash_desc *sdesc; 229 int size, ret = 0; 230 231 spin_lock_init(&rng->jent_lock); 232 233 /* Use SHA3-256 as conditioner */ 234 hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0); 235 if (IS_ERR(hash)) { 236 pr_err("Cannot allocate conditioning digest\n"); 237 return PTR_ERR(hash); 238 } 239 rng->tfm = hash; 240 241 size = sizeof(struct shash_desc) + crypto_shash_descsize(hash); 242 sdesc = kmalloc(size, GFP_KERNEL); 243 if (!sdesc) { 244 ret = -ENOMEM; 245 goto err; 246 } 247 248 sdesc->tfm = hash; 249 crypto_shash_init(sdesc); 250 rng->sdesc = sdesc; 251 252 rng->entropy_collector = 253 jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, 254 sdesc); 255 if (!rng->entropy_collector) { 256 ret = -ENOMEM; 257 goto err; 258 } 259 260 spin_lock_init(&rng->jent_lock); 261 return 0; 262 263 err: 264 jent_kcapi_cleanup(tfm); 265 return ret; 266 } 267 268 static int jent_kcapi_random(struct crypto_rng *tfm, 269 const u8 *src, unsigned int slen, 270 u8 *rdata, unsigned int dlen) 271 { 272 struct jitterentropy *rng = crypto_rng_ctx(tfm); 273 int ret = 0; 274 275 spin_lock(&rng->jent_lock); 276 277 ret = jent_read_entropy(rng->entropy_collector, rdata, dlen); 278 279 if (ret == -3) { 280 /* Handle permanent health test error */ 281 /* 282 * If the kernel was booted with fips=1, it implies that 283 * the entire kernel acts as a FIPS 140 module. In this case 284 * an SP800-90B permanent health test error is treated as 285 * a FIPS module error. 286 */ 287 if (fips_enabled) 288 panic("Jitter RNG permanent health test failure\n"); 289 290 pr_err("Jitter RNG permanent health test failure\n"); 291 ret = -EFAULT; 292 } else if (ret == -2) { 293 /* Handle intermittent health test error */ 294 pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n"); 295 ret = -EAGAIN; 296 } else if (ret == -1) { 297 /* Handle other errors */ 298 ret = -EINVAL; 299 } 300 301 spin_unlock(&rng->jent_lock); 302 303 return ret; 304 } 305 306 static int jent_kcapi_reset(struct crypto_rng *tfm, 307 const u8 *seed, unsigned int slen) 308 { 309 return 0; 310 } 311 312 static struct rng_alg jent_alg = { 313 .generate = jent_kcapi_random, 314 .seed = jent_kcapi_reset, 315 .seedsize = 0, 316 .base = { 317 .cra_name = "jitterentropy_rng", 318 .cra_driver_name = "jitterentropy_rng", 319 .cra_priority = 100, 320 .cra_ctxsize = sizeof(struct jitterentropy), 321 .cra_module = THIS_MODULE, 322 .cra_init = jent_kcapi_init, 323 .cra_exit = jent_kcapi_cleanup, 324 } 325 }; 326 327 static int __init jent_mod_init(void) 328 { 329 SHASH_DESC_ON_STACK(desc, tfm); 330 struct crypto_shash *tfm; 331 int ret = 0; 332 333 jent_testing_init(); 334 335 tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0); 336 if (IS_ERR(tfm)) { 337 jent_testing_exit(); 338 return PTR_ERR(tfm); 339 } 340 341 desc->tfm = tfm; 342 crypto_shash_init(desc); 343 ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc, NULL); 344 shash_desc_zero(desc); 345 crypto_free_shash(tfm); 346 if (ret) { 347 /* Handle permanent health test error */ 348 if (fips_enabled) 349 panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); 350 351 jent_testing_exit(); 352 pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); 353 return -EFAULT; 354 } 355 return crypto_register_rng(&jent_alg); 356 } 357 358 static void __exit jent_mod_exit(void) 359 { 360 jent_testing_exit(); 361 crypto_unregister_rng(&jent_alg); 362 } 363 364 module_init(jent_mod_init); 365 module_exit(jent_mod_exit); 366 367 MODULE_LICENSE("Dual BSD/GPL"); 368 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 369 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter"); 370 MODULE_ALIAS_CRYPTO("jitterentropy_rng"); 371