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
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	memzero_explicit(ptr, len);
65	kvfree(ptr);
66}
67
68void *jent_zalloc(unsigned int len)
69{
70	return kzalloc(len, GFP_KERNEL);
71}
72
73void jent_zfree(void *ptr)
74{
75	kfree_sensitive(ptr);
76}
77
78/*
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.
82 *
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.
86 */
87void jent_get_nstime(__u64 *out)
88{
89	__u64 tmp = 0;
90
91	tmp = random_get_entropy();
92
93	/*
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.
97	 */
98	if (tmp == 0)
99		tmp = ktime_get_ns();
100
101	*out = tmp;
102	jent_raw_hires_entropy_store(tmp);
103}
104
105int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
106		   unsigned int addtl_len, __u64 hash_loop_cnt,
107		   unsigned int stuck)
108{
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];
112	__u64 j = 0;
113	int ret;
114
115	desc->tfm = hash_state_desc->tfm;
116
117	if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) {
118		pr_warn_ratelimited("Unexpected digest size\n");
119		return -EINVAL;
120	}
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(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		ret = crypto_shash_update(hash_state_desc, (u8 *)&time,
163					  sizeof(__u64));
164	}
165
166err:
167	shash_desc_zero(desc);
168	memzero_explicit(intermediary, sizeof(intermediary));
169
170	return ret;
171}
172
173int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len)
174{
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,
181				      sizeof(jent_block));
182
183	if (!ret && dst_len)
184		memcpy(dst, jent_block, dst_len);
185
186	memzero_explicit(jent_block, sizeof(jent_block));
187	return ret;
188}
189
190/***************************************************************************
191 * Kernel crypto API interface
192 ***************************************************************************/
193
194struct jitterentropy {
195	spinlock_t jent_lock;
196	struct rand_data *entropy_collector;
197	struct crypto_shash *tfm;
198	struct shash_desc *sdesc;
199};
200
201static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
202{
203	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
204
205	spin_lock(&rng->jent_lock);
206
207	if (rng->sdesc) {
208		shash_desc_zero(rng->sdesc);
209		kfree(rng->sdesc);
210	}
211	rng->sdesc = NULL;
212
213	if (rng->tfm)
214		crypto_free_shash(rng->tfm);
215	rng->tfm = NULL;
216
217	if (rng->entropy_collector)
218		jent_entropy_collector_free(rng->entropy_collector);
219	rng->entropy_collector = NULL;
220	spin_unlock(&rng->jent_lock);
221}
222
223static int jent_kcapi_init(struct crypto_tfm *tfm)
224{
225	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
226	struct crypto_shash *hash;
227	struct shash_desc *sdesc;
228	int size, ret = 0;
229
230	spin_lock_init(&rng->jent_lock);
231
232	/*
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.
240	 */
241	hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
242	if (IS_ERR(hash)) {
243		pr_err("Cannot allocate conditioning digest\n");
244		return PTR_ERR(hash);
245	}
246	rng->tfm = hash;
247
248	size = sizeof(struct shash_desc) + crypto_shash_descsize(hash);
249	sdesc = kmalloc(size, GFP_KERNEL);
250	if (!sdesc) {
251		ret = -ENOMEM;
252		goto err;
253	}
254
255	sdesc->tfm = hash;
256	crypto_shash_init(sdesc);
257	rng->sdesc = sdesc;
258
259	rng->entropy_collector =
260		jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0,
261					     sdesc);
262	if (!rng->entropy_collector) {
263		ret = -ENOMEM;
264		goto err;
265	}
266
267	spin_lock_init(&rng->jent_lock);
268	return 0;
269
270err:
271	jent_kcapi_cleanup(tfm);
272	return ret;
273}
274
275static int jent_kcapi_random(struct crypto_rng *tfm,
276			     const u8 *src, unsigned int slen,
277			     u8 *rdata, unsigned int dlen)
278{
279	struct jitterentropy *rng = crypto_rng_ctx(tfm);
280	int ret = 0;
281
282	spin_lock(&rng->jent_lock);
283
284	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
285
286	if (ret == -3) {
287		/* Handle permanent health test error */
288		/*
289		 * If the kernel was booted with fips=1, it implies that
290		 * the entire kernel acts as a FIPS 140 module. In this case
291		 * an SP800-90B permanent health test error is treated as
292		 * a FIPS module error.
293		 */
294		if (fips_enabled)
295			panic("Jitter RNG permanent health test failure\n");
296
297		pr_err("Jitter RNG permanent health test failure\n");
298		ret = -EFAULT;
299	} else if (ret == -2) {
300		/* Handle intermittent health test error */
301		pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n");
302		ret = -EAGAIN;
303	} else if (ret == -1) {
304		/* Handle other errors */
305		ret = -EINVAL;
306	}
307
308	spin_unlock(&rng->jent_lock);
309
310	return ret;
311}
312
313static int jent_kcapi_reset(struct crypto_rng *tfm,
314			    const u8 *seed, unsigned int slen)
315{
316	return 0;
317}
318
319static struct rng_alg jent_alg = {
320	.generate		= jent_kcapi_random,
321	.seed			= jent_kcapi_reset,
322	.seedsize		= 0,
323	.base			= {
324		.cra_name               = "jitterentropy_rng",
325		.cra_driver_name        = "jitterentropy_rng",
326		.cra_priority           = 100,
327		.cra_ctxsize            = sizeof(struct jitterentropy),
328		.cra_module             = THIS_MODULE,
329		.cra_init               = jent_kcapi_init,
330		.cra_exit               = jent_kcapi_cleanup,
331	}
332};
333
334static int __init jent_mod_init(void)
335{
336	SHASH_DESC_ON_STACK(desc, tfm);
337	struct crypto_shash *tfm;
338	int ret = 0;
339
340	jent_testing_init();
341
342	tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
343	if (IS_ERR(tfm)) {
344		jent_testing_exit();
345		return PTR_ERR(tfm);
346	}
347
348	desc->tfm = tfm;
349	crypto_shash_init(desc);
350	ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc, NULL);
351	shash_desc_zero(desc);
352	crypto_free_shash(tfm);
353	if (ret) {
354		/* Handle permanent health test error */
355		if (fips_enabled)
356			panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
357
358		jent_testing_exit();
359		pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
360		return -EFAULT;
361	}
362	return crypto_register_rng(&jent_alg);
363}
364
365static void __exit jent_mod_exit(void)
366{
367	jent_testing_exit();
368	crypto_unregister_rng(&jent_alg);
369}
370
371module_init(jent_mod_init);
372module_exit(jent_mod_exit);
373
374MODULE_LICENSE("Dual BSD/GPL");
375MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
376MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
377MODULE_ALIAS_CRYPTO("jitterentropy_rng");
378