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/module.h> 41 #include <linux/slab.h> 42 #include <linux/fips.h> 43 #include <linux/time.h> 44 #include <linux/crypto.h> 45 #include <crypto/internal/rng.h> 46 47 #include "jitterentropy.h" 48 49 /*************************************************************************** 50 * Helper function 51 ***************************************************************************/ 52 53 void *jent_zalloc(unsigned int len) 54 { 55 return kzalloc(len, GFP_KERNEL); 56 } 57 58 void jent_zfree(void *ptr) 59 { 60 kfree_sensitive(ptr); 61 } 62 63 int jent_fips_enabled(void) 64 { 65 return fips_enabled; 66 } 67 68 void jent_panic(char *s) 69 { 70 panic("%s", s); 71 } 72 73 void 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 */ 87 void 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 ***************************************************************************/ 107 108 struct jitterentropy { 109 spinlock_t jent_lock; 110 struct rand_data *entropy_collector; 111 unsigned int reset_cnt; 112 }; 113 114 static 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 } 126 127 static 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 } 137 138 static 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 } 171 172 out: 173 spin_unlock(&rng->jent_lock); 174 175 return ret; 176 } 177 178 static int jent_kcapi_reset(struct crypto_rng *tfm, 179 const u8 *seed, unsigned int slen) 180 { 181 return 0; 182 } 183 184 static 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 }; 199 200 static 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 } 211 212 static void __exit jent_mod_exit(void) 213 { 214 crypto_unregister_rng(&jent_alg); 215 } 216 217 module_init(jent_mod_init); 218 module_exit(jent_mod_exit); 219 220 MODULE_LICENSE("Dual BSD/GPL"); 221 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 222 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter"); 223 MODULE_ALIAS_CRYPTO("jitterentropy_rng"); 224