/* * Non-physical true random number generator based on timing jitter -- * Linux Kernel Crypto API specific code * * Copyright Stephan Mueller , 2015 - 2023 * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, and the entire permission notice in its entirety, * including the disclaimer of warranties. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. The name of the author may not be used to endorse or promote * products derived from this software without specific prior * written permission. * * ALTERNATIVELY, this product may be distributed under the terms of * the GNU General Public License, in which case the provisions of the GPL2 are * required INSTEAD OF the above restrictions. (This clause is * necessary due to a potential bad interaction between the GPL and * the restrictions contained in a BSD-style copyright.) * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH * DAMAGE. */ #include #include #include #include #include #include #include #include #include "jitterentropy.h" #define JENT_CONDITIONING_HASH "sha3-256-generic" /*************************************************************************** * Helper function ***************************************************************************/ void *jent_zalloc(unsigned int len) { return kzalloc(len, GFP_KERNEL); } void jent_zfree(void *ptr) { kfree_sensitive(ptr); } /* * Obtain a high-resolution time stamp value. The time stamp is used to measure * the execution time of a given code path and its variations. Hence, the time * stamp must have a sufficiently high resolution. * * Note, if the function returns zero because a given architecture does not * implement a high-resolution time stamp, the RNG code's runtime test * will detect it and will not produce output. */ void jent_get_nstime(__u64 *out) { __u64 tmp = 0; tmp = random_get_entropy(); /* * If random_get_entropy does not return a value, i.e. it is not * implemented for a given architecture, use a clock source. * hoping that there are timers we can work with. */ if (tmp == 0) tmp = ktime_get_ns(); *out = tmp; } int jent_hash_time(void *hash_state, __u64 time, u8 *addtl, unsigned int addtl_len, __u64 hash_loop_cnt, unsigned int stuck) { struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state; SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm); u8 intermediary[SHA3_256_DIGEST_SIZE]; __u64 j = 0; int ret; desc->tfm = hash_state_desc->tfm; if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) { pr_warn_ratelimited("Unexpected digest size\n"); return -EINVAL; } /* * This loop fills a buffer which is injected into the entropy pool. * The main reason for this loop is to execute something over which we * can perform a timing measurement. The injection of the resulting * data into the pool is performed to ensure the result is used and * the compiler cannot optimize the loop away in case the result is not * used at all. Yet that data is considered "additional information" * considering the terminology from SP800-90A without any entropy. * * Note, it does not matter which or how much data you inject, we are * interested in one Keccack1600 compression operation performed with * the crypto_shash_final. */ for (j = 0; j < hash_loop_cnt; j++) { ret = crypto_shash_init(desc) ?: crypto_shash_update(desc, intermediary, sizeof(intermediary)) ?: crypto_shash_finup(desc, addtl, addtl_len, intermediary); if (ret) goto err; } /* * Inject the data from the previous loop into the pool. This data is * not considered to contain any entropy, but it stirs the pool a bit. */ ret = crypto_shash_update(desc, intermediary, sizeof(intermediary)); if (ret) goto err; /* * Insert the time stamp into the hash context representing the pool. * * If the time stamp is stuck, do not finally insert the value into the * entropy pool. Although this operation should not do any harm even * when the time stamp has no entropy, SP800-90B requires that any * conditioning operation to have an identical amount of input data * according to section 3.1.5. */ if (!stuck) { ret = crypto_shash_update(hash_state_desc, (u8 *)&time, sizeof(__u64)); } err: shash_desc_zero(desc); memzero_explicit(intermediary, sizeof(intermediary)); return ret; } int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len) { struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state; u8 jent_block[SHA3_256_DIGEST_SIZE]; /* Obtain data from entropy pool and re-initialize it */ int ret = crypto_shash_final(hash_state_desc, jent_block) ?: crypto_shash_init(hash_state_desc) ?: crypto_shash_update(hash_state_desc, jent_block, sizeof(jent_block)); if (!ret && dst_len) memcpy(dst, jent_block, dst_len); memzero_explicit(jent_block, sizeof(jent_block)); return ret; } /*************************************************************************** * Kernel crypto API interface ***************************************************************************/ struct jitterentropy { spinlock_t jent_lock; struct rand_data *entropy_collector; struct crypto_shash *tfm; struct shash_desc *sdesc; }; static void jent_kcapi_cleanup(struct crypto_tfm *tfm) { struct jitterentropy *rng = crypto_tfm_ctx(tfm); spin_lock(&rng->jent_lock); if (rng->sdesc) { shash_desc_zero(rng->sdesc); kfree(rng->sdesc); } rng->sdesc = NULL; if (rng->tfm) crypto_free_shash(rng->tfm); rng->tfm = NULL; if (rng->entropy_collector) jent_entropy_collector_free(rng->entropy_collector); rng->entropy_collector = NULL; spin_unlock(&rng->jent_lock); } static int jent_kcapi_init(struct crypto_tfm *tfm) { struct jitterentropy *rng = crypto_tfm_ctx(tfm); struct crypto_shash *hash; struct shash_desc *sdesc; int size, ret = 0; spin_lock_init(&rng->jent_lock); /* * Use SHA3-256 as conditioner. We allocate only the generic * implementation as we are not interested in high-performance. The * execution time of the SHA3 operation is measured and adds to the * Jitter RNG's unpredictable behavior. If we have a slower hash * implementation, the execution timing variations are larger. When * using a fast implementation, we would need to call it more often * as its variations are lower. */ hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0); if (IS_ERR(hash)) { pr_err("Cannot allocate conditioning digest\n"); return PTR_ERR(hash); } rng->tfm = hash; size = sizeof(struct shash_desc) + crypto_shash_descsize(hash); sdesc = kmalloc(size, GFP_KERNEL); if (!sdesc) { ret = -ENOMEM; goto err; } sdesc->tfm = hash; crypto_shash_init(sdesc); rng->sdesc = sdesc; rng->entropy_collector = jent_entropy_collector_alloc(1, 0, sdesc); if (!rng->entropy_collector) { ret = -ENOMEM; goto err; } spin_lock_init(&rng->jent_lock); return 0; err: jent_kcapi_cleanup(tfm); return ret; } static int jent_kcapi_random(struct crypto_rng *tfm, const u8 *src, unsigned int slen, u8 *rdata, unsigned int dlen) { struct jitterentropy *rng = crypto_rng_ctx(tfm); int ret = 0; spin_lock(&rng->jent_lock); ret = jent_read_entropy(rng->entropy_collector, rdata, dlen); if (ret == -3) { /* Handle permanent health test error */ /* * If the kernel was booted with fips=1, it implies that * the entire kernel acts as a FIPS 140 module. In this case * an SP800-90B permanent health test error is treated as * a FIPS module error. */ if (fips_enabled) panic("Jitter RNG permanent health test failure\n"); pr_err("Jitter RNG permanent health test failure\n"); ret = -EFAULT; } else if (ret == -2) { /* Handle intermittent health test error */ pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n"); ret = -EAGAIN; } else if (ret == -1) { /* Handle other errors */ ret = -EINVAL; } spin_unlock(&rng->jent_lock); return ret; } static int jent_kcapi_reset(struct crypto_rng *tfm, const u8 *seed, unsigned int slen) { return 0; } static struct rng_alg jent_alg = { .generate = jent_kcapi_random, .seed = jent_kcapi_reset, .seedsize = 0, .base = { .cra_name = "jitterentropy_rng", .cra_driver_name = "jitterentropy_rng", .cra_priority = 100, .cra_ctxsize = sizeof(struct jitterentropy), .cra_module = THIS_MODULE, .cra_init = jent_kcapi_init, .cra_exit = jent_kcapi_cleanup, } }; static int __init jent_mod_init(void) { SHASH_DESC_ON_STACK(desc, tfm); struct crypto_shash *tfm; int ret = 0; tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0); if (IS_ERR(tfm)) return PTR_ERR(tfm); desc->tfm = tfm; crypto_shash_init(desc); ret = jent_entropy_init(desc); shash_desc_zero(desc); crypto_free_shash(tfm); if (ret) { /* Handle permanent health test error */ if (fips_enabled) panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); return -EFAULT; } return crypto_register_rng(&jent_alg); } static void __exit jent_mod_exit(void) { crypto_unregister_rng(&jent_alg); } module_init(jent_mod_init); module_exit(jent_mod_exit); MODULE_LICENSE("Dual BSD/GPL"); MODULE_AUTHOR("Stephan Mueller "); MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter"); MODULE_ALIAS_CRYPTO("jitterentropy_rng");