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_zalloc(unsigned int len) 58 { 59 return kzalloc(len, GFP_KERNEL); 60 } 61 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 */ 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 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 } 161 162 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 }; 189 190 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 } 211 212 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 } 261 262 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 } 299 300 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 }; 320 321 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 } 351 352 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