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1/*2 * Non-physical true random number generator based on timing jitter --3 * Linux Kernel Crypto API specific code4 *5 * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 20236 *7 * Redistribution and use in source and binary forms, with or without8 * modification, are permitted provided that the following conditions9 * are met:10 * 1. Redistributions of source code must retain the above copyright11 * 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 copyright14 * notice, this list of conditions and the following disclaimer in the15 * documentation and/or other materials provided with the distribution.16 * 3. The name of the author may not be used to endorse or promote17 * products derived from this software without specific prior18 * written permission.19 *20 * ALTERNATIVELY, this product may be distributed under the terms of21 * the GNU General Public License, in which case the provisions of the GPL2 are22 * required INSTEAD OF the above restrictions. (This clause is23 * necessary due to a potential bad interaction between the GPL and24 * the restrictions contained in a BSD-style copyright.)25 *26 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED27 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES28 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF29 * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE30 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT32 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR33 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF34 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT35 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE36 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH37 * 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 function55 ***************************************************************************/56 57void *jent_kvzalloc(unsigned int len)58{59 return kvzalloc(len, GFP_KERNEL);60}61 62void jent_kvzfree(void *ptr, unsigned int len)63{64 kvfree_sensitive(ptr, len);65}66 67void *jent_zalloc(unsigned int len)68{69 return kzalloc(len, GFP_KERNEL);70}71 72void 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 measure79 * the execution time of a given code path and its variations. Hence, the time80 * stamp must have a sufficiently high resolution.81 *82 * Note, if the function returns zero because a given architecture does not83 * implement a high-resolution time stamp, the RNG code's runtime test84 * will detect it and will not produce output.85 */86void 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 not94 * 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 104int 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 we124 * can perform a timing measurement. The injection of the resulting125 * data into the pool is performed to ensure the result is used and126 * the compiler cannot optimize the loop away in case the result is not127 * 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 are131 * interested in one Keccack1600 compression operation performed with132 * 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 is145 * 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 the155 * entropy pool. Although this operation should not do any harm even156 * when the time stamp has no entropy, SP800-90B requires that any157 * conditioning operation to have an identical amount of input data158 * 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 165err:166 shash_desc_zero(desc);167 memzero_explicit(intermediary, sizeof(intermediary));168 169 return ret;170}171 172int 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 interface191 ***************************************************************************/192 193struct jitterentropy {194 spinlock_t jent_lock;195 struct rand_data *entropy_collector;196 struct crypto_shash *tfm;197 struct shash_desc *sdesc;198};199 200static 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 222static 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 generic233 * implementation as we are not interested in high-performance. The234 * execution time of the SHA3 operation is measured and adds to the235 * Jitter RNG's unpredictable behavior. If we have a slower hash236 * implementation, the execution timing variations are larger. When237 * using a fast implementation, we would need to call it more often238 * 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 269err:270 jent_kcapi_cleanup(tfm);271 return ret;272}273 274static 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 that289 * the entire kernel acts as a FIPS 140 module. In this case290 * an SP800-90B permanent health test error is treated as291 * 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 312static int jent_kcapi_reset(struct crypto_rng *tfm,313 const u8 *seed, unsigned int slen)314{315 return 0;316}317 318static 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 333static 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 364static void __exit jent_mod_exit(void)365{366 jent_testing_exit();367 crypto_unregister_rng(&jent_alg);368}369 370module_init(jent_mod_init);371module_exit(jent_mod_exit);372 373MODULE_LICENSE("Dual BSD/GPL");374MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");375MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");376MODULE_ALIAS_CRYPTO("jitterentropy_rng");377