jitterentropy-kcapi.c

  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
 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 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 */
 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 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
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	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
167err:
168	shash_desc_zero(desc);
169	memzero_explicit(intermediary, sizeof(intermediary));
170
171	return ret;
172}
173
174int 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
195struct jitterentropy {
196	spinlock_t jent_lock;
197	struct rand_data *entropy_collector;
198	struct crypto_shash *tfm;
199	struct shash_desc *sdesc;
200};
201
202static 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
224static 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
263err:
264	jent_kcapi_cleanup(tfm);
265	return ret;
266}
267
268static 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
306static int jent_kcapi_reset(struct crypto_rng *tfm,
307			    const u8 *seed, unsigned int slen)
308{
309	return 0;
310}
311
312static 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
327static 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
358static void __exit jent_mod_exit(void)
359{
360	jent_testing_exit();
361	crypto_unregister_rng(&jent_alg);
362}
363
364module_init(jent_mod_init);
365module_exit(jent_mod_exit);
366
367MODULE_LICENSE("Dual BSD/GPL");
368MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
369MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
370MODULE_ALIAS_CRYPTO("jitterentropy_rng");