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
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 <linux/kernel.h>
41#include <linux/module.h>
42#include <linux/slab.h>
43#include <linux/fips.h>
44#include <linux/time.h>
45#include <crypto/internal/rng.h>
46
47#include "jitterentropy.h"
48
49/***************************************************************************
50 * Helper function
51 ***************************************************************************/
52
53void *jent_zalloc(unsigned int len)
54{
55	return kzalloc(len, GFP_KERNEL);
56}
57
58void jent_zfree(void *ptr)
59{
60	kfree_sensitive(ptr);
61}
62
63int jent_fips_enabled(void)
64{
65	return fips_enabled;
66}
67
68void jent_panic(char *s)
69{
70	panic("%s", s);
71}
72
73void jent_memcpy(void *dest, const void *src, unsigned int n)
74{
75	memcpy(dest, src, n);
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}
103
104/***************************************************************************
105 * Kernel crypto API interface
106 ***************************************************************************/
107
108struct jitterentropy {
109	spinlock_t jent_lock;
110	struct rand_data *entropy_collector;
111	unsigned int reset_cnt;
112};
113
114static int jent_kcapi_init(struct crypto_tfm *tfm)
115{
116	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
117	int ret = 0;
118
119	rng->entropy_collector = jent_entropy_collector_alloc(1, 0);
120	if (!rng->entropy_collector)
121		ret = -ENOMEM;
122
123	spin_lock_init(&rng->jent_lock);
124	return ret;
125}
126
127static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
128{
129	struct jitterentropy *rng = crypto_tfm_ctx(tfm);
130
131	spin_lock(&rng->jent_lock);
132	if (rng->entropy_collector)
133		jent_entropy_collector_free(rng->entropy_collector);
134	rng->entropy_collector = NULL;
135	spin_unlock(&rng->jent_lock);
136}
137
138static int jent_kcapi_random(struct crypto_rng *tfm,
139			     const u8 *src, unsigned int slen,
140			     u8 *rdata, unsigned int dlen)
141{
142	struct jitterentropy *rng = crypto_rng_ctx(tfm);
143	int ret = 0;
144
145	spin_lock(&rng->jent_lock);
146
147	/* Return a permanent error in case we had too many resets in a row. */
148	if (rng->reset_cnt > (1<<10)) {
149		ret = -EFAULT;
150		goto out;
151	}
152
153	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
154
155	/* Reset RNG in case of health failures */
156	if (ret < -1) {
157		pr_warn_ratelimited("Reset Jitter RNG due to health test failure: %s failure\n",
158				    (ret == -2) ? "Repetition Count Test" :
159						  "Adaptive Proportion Test");
160
161		rng->reset_cnt++;
162
163		ret = -EAGAIN;
164	} else {
165		rng->reset_cnt = 0;
166
167		/* Convert the Jitter RNG error into a usable error code */
168		if (ret == -1)
169			ret = -EINVAL;
170	}
171
172out:
173	spin_unlock(&rng->jent_lock);
174
175	return ret;
176}
177
178static int jent_kcapi_reset(struct crypto_rng *tfm,
179			    const u8 *seed, unsigned int slen)
180{
181	return 0;
182}
183
184static struct rng_alg jent_alg = {
185	.generate		= jent_kcapi_random,
186	.seed			= jent_kcapi_reset,
187	.seedsize		= 0,
188	.base			= {
189		.cra_name               = "jitterentropy_rng",
190		.cra_driver_name        = "jitterentropy_rng",
191		.cra_priority           = 100,
192		.cra_ctxsize            = sizeof(struct jitterentropy),
193		.cra_module             = THIS_MODULE,
194		.cra_init               = jent_kcapi_init,
195		.cra_exit               = jent_kcapi_cleanup,
196
197	}
198};
199
200static int __init jent_mod_init(void)
201{
202	int ret = 0;
203
204	ret = jent_entropy_init();
205	if (ret) {
206		pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
207		return -EFAULT;
208	}
209	return crypto_register_rng(&jent_alg);
210}
211
212static void __exit jent_mod_exit(void)
213{
214	crypto_unregister_rng(&jent_alg);
215}
216
217module_init(jent_mod_init);
218module_exit(jent_mod_exit);
219
220MODULE_LICENSE("Dual BSD/GPL");
221MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
222MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
223MODULE_ALIAS_CRYPTO("jitterentropy_rng");
224