2 * Non-physical true random number generator based on timing jitter --
3 * Linux Kernel Crypto API specific code
5 * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2023
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8 * modification, are permitted provided that the following conditions
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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>
49 #include "jitterentropy.h"
51 #define JENT_CONDITIONING_HASH "sha3-256-generic"
53 /***************************************************************************
55 ***************************************************************************/
57 void *jent_kvzalloc(unsigned int len)
59 return kvzalloc(len, GFP_KERNEL);
62 void jent_kvzfree(void *ptr, unsigned int len)
64 memzero_explicit(ptr, len);
68 void *jent_zalloc(unsigned int len)
70 return kzalloc(len, GFP_KERNEL);
73 void jent_zfree(void *ptr)
79 * Obtain a high-resolution time stamp value. The time stamp is used to measure
80 * the execution time of a given code path and its variations. Hence, the time
81 * stamp must have a sufficiently high resolution.
83 * Note, if the function returns zero because a given architecture does not
84 * implement a high-resolution time stamp, the RNG code's runtime test
85 * will detect it and will not produce output.
87 void jent_get_nstime(__u64 *out)
91 tmp = random_get_entropy();
94 * If random_get_entropy does not return a value, i.e. it is not
95 * implemented for a given architecture, use a clock source.
96 * hoping that there are timers we can work with.
102 jent_raw_hires_entropy_store(tmp);
105 int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
106 unsigned int addtl_len, __u64 hash_loop_cnt,
109 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
110 SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm);
111 u8 intermediary[SHA3_256_DIGEST_SIZE];
115 desc->tfm = hash_state_desc->tfm;
117 if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) {
118 pr_warn_ratelimited("Unexpected digest size\n");
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.
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.
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);
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.
148 ret = crypto_shash_update(desc, intermediary, sizeof(intermediary));
153 * Insert the time stamp into the hash context representing the pool.
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.
162 ret = crypto_shash_update(hash_state_desc, (u8 *)&time,
167 shash_desc_zero(desc);
168 memzero_explicit(intermediary, sizeof(intermediary));
173 int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len)
175 struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
176 u8 jent_block[SHA3_256_DIGEST_SIZE];
177 /* Obtain data from entropy pool and re-initialize it */
178 int ret = crypto_shash_final(hash_state_desc, jent_block) ?:
179 crypto_shash_init(hash_state_desc) ?:
180 crypto_shash_update(hash_state_desc, jent_block,
184 memcpy(dst, jent_block, dst_len);
186 memzero_explicit(jent_block, sizeof(jent_block));
190 /***************************************************************************
191 * Kernel crypto API interface
192 ***************************************************************************/
194 struct jitterentropy {
195 spinlock_t jent_lock;
196 struct rand_data *entropy_collector;
197 struct crypto_shash *tfm;
198 struct shash_desc *sdesc;
201 static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
203 struct jitterentropy *rng = crypto_tfm_ctx(tfm);
205 spin_lock(&rng->jent_lock);
208 shash_desc_zero(rng->sdesc);
214 crypto_free_shash(rng->tfm);
217 if (rng->entropy_collector)
218 jent_entropy_collector_free(rng->entropy_collector);
219 rng->entropy_collector = NULL;
220 spin_unlock(&rng->jent_lock);
223 static int jent_kcapi_init(struct crypto_tfm *tfm)
225 struct jitterentropy *rng = crypto_tfm_ctx(tfm);
226 struct crypto_shash *hash;
227 struct shash_desc *sdesc;
230 spin_lock_init(&rng->jent_lock);
233 * Use SHA3-256 as conditioner. We allocate only the generic
234 * implementation as we are not interested in high-performance. The
235 * execution time of the SHA3 operation is measured and adds to the
236 * Jitter RNG's unpredictable behavior. If we have a slower hash
237 * implementation, the execution timing variations are larger. When
238 * using a fast implementation, we would need to call it more often
239 * as its variations are lower.
241 hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
243 pr_err("Cannot allocate conditioning digest\n");
244 return PTR_ERR(hash);
248 size = sizeof(struct shash_desc) + crypto_shash_descsize(hash);
249 sdesc = kmalloc(size, GFP_KERNEL);
256 crypto_shash_init(sdesc);
259 rng->entropy_collector = jent_entropy_collector_alloc(0, 0, sdesc);
260 if (!rng->entropy_collector) {
265 spin_lock_init(&rng->jent_lock);
269 jent_kcapi_cleanup(tfm);
273 static int jent_kcapi_random(struct crypto_rng *tfm,
274 const u8 *src, unsigned int slen,
275 u8 *rdata, unsigned int dlen)
277 struct jitterentropy *rng = crypto_rng_ctx(tfm);
280 spin_lock(&rng->jent_lock);
282 ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
285 /* Handle permanent health test error */
287 * If the kernel was booted with fips=1, it implies that
288 * the entire kernel acts as a FIPS 140 module. In this case
289 * an SP800-90B permanent health test error is treated as
290 * a FIPS module error.
293 panic("Jitter RNG permanent health test failure\n");
295 pr_err("Jitter RNG permanent health test failure\n");
297 } else if (ret == -2) {
298 /* Handle intermittent health test error */
299 pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n");
301 } else if (ret == -1) {
302 /* Handle other errors */
306 spin_unlock(&rng->jent_lock);
311 static int jent_kcapi_reset(struct crypto_rng *tfm,
312 const u8 *seed, unsigned int slen)
317 static struct rng_alg jent_alg = {
318 .generate = jent_kcapi_random,
319 .seed = jent_kcapi_reset,
322 .cra_name = "jitterentropy_rng",
323 .cra_driver_name = "jitterentropy_rng",
325 .cra_ctxsize = sizeof(struct jitterentropy),
326 .cra_module = THIS_MODULE,
327 .cra_init = jent_kcapi_init,
328 .cra_exit = jent_kcapi_cleanup,
332 static int __init jent_mod_init(void)
334 SHASH_DESC_ON_STACK(desc, tfm);
335 struct crypto_shash *tfm;
340 tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
347 crypto_shash_init(desc);
348 ret = jent_entropy_init(0, 0, desc);
349 shash_desc_zero(desc);
350 crypto_free_shash(tfm);
352 /* Handle permanent health test error */
354 panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
357 pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
360 return crypto_register_rng(&jent_alg);
363 static void __exit jent_mod_exit(void)
366 crypto_unregister_rng(&jent_alg);
369 module_init(jent_mod_init);
370 module_exit(jent_mod_exit);
372 MODULE_LICENSE("Dual BSD/GPL");
373 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
374 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
375 MODULE_ALIAS_CRYPTO("jitterentropy_rng");