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/time.h> 44 #include <crypto/internal/rng.h> 45 46 #include "jitterentropy.h" 47 48 /*************************************************************************** 49 * Helper function 50 ***************************************************************************/ 51 52 void *jent_zalloc(unsigned int len) 53 { 54 return kzalloc(len, GFP_KERNEL); 55 } 56 57 void jent_zfree(void *ptr) 58 { 59 kfree_sensitive(ptr); 60 } 61 62 void jent_panic(char *s) 63 { 64 panic("%s", s); 65 } 66 67 void jent_memcpy(void *dest, const void *src, unsigned int n) 68 { 69 memcpy(dest, src, n); 70 } 71 72 /* 73 * Obtain a high-resolution time stamp value. The time stamp is used to measure 74 * the execution time of a given code path and its variations. Hence, the time 75 * stamp must have a sufficiently high resolution. 76 * 77 * Note, if the function returns zero because a given architecture does not 78 * implement a high-resolution time stamp, the RNG code's runtime test 79 * will detect it and will not produce output. 80 */ 81 void jent_get_nstime(__u64 *out) 82 { 83 __u64 tmp = 0; 84 85 tmp = random_get_entropy(); 86 87 /* 88 * If random_get_entropy does not return a value, i.e. it is not 89 * implemented for a given architecture, use a clock source. 90 * hoping that there are timers we can work with. 91 */ 92 if (tmp == 0) 93 tmp = ktime_get_ns(); 94 95 *out = tmp; 96 } 97 98 /*************************************************************************** 99 * Kernel crypto API interface 100 ***************************************************************************/ 101 102 struct jitterentropy { 103 spinlock_t jent_lock; 104 struct rand_data *entropy_collector; 105 unsigned int reset_cnt; 106 }; 107 108 static int jent_kcapi_init(struct crypto_tfm *tfm) 109 { 110 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 111 int ret = 0; 112 113 rng->entropy_collector = jent_entropy_collector_alloc(1, 0); 114 if (!rng->entropy_collector) 115 ret = -ENOMEM; 116 117 spin_lock_init(&rng->jent_lock); 118 return ret; 119 } 120 121 static void jent_kcapi_cleanup(struct crypto_tfm *tfm) 122 { 123 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 124 125 spin_lock(&rng->jent_lock); 126 if (rng->entropy_collector) 127 jent_entropy_collector_free(rng->entropy_collector); 128 rng->entropy_collector = NULL; 129 spin_unlock(&rng->jent_lock); 130 } 131 132 static int jent_kcapi_random(struct crypto_rng *tfm, 133 const u8 *src, unsigned int slen, 134 u8 *rdata, unsigned int dlen) 135 { 136 struct jitterentropy *rng = crypto_rng_ctx(tfm); 137 int ret = 0; 138 139 spin_lock(&rng->jent_lock); 140 141 /* Return a permanent error in case we had too many resets in a row. */ 142 if (rng->reset_cnt > (1<<10)) { 143 ret = -EFAULT; 144 goto out; 145 } 146 147 ret = jent_read_entropy(rng->entropy_collector, rdata, dlen); 148 149 /* Reset RNG in case of health failures */ 150 if (ret < -1) { 151 pr_warn_ratelimited("Reset Jitter RNG due to health test failure: %s failure\n", 152 (ret == -2) ? "Repetition Count Test" : 153 "Adaptive Proportion Test"); 154 155 rng->reset_cnt++; 156 157 ret = -EAGAIN; 158 } else { 159 rng->reset_cnt = 0; 160 161 /* Convert the Jitter RNG error into a usable error code */ 162 if (ret == -1) 163 ret = -EINVAL; 164 } 165 166 out: 167 spin_unlock(&rng->jent_lock); 168 169 return ret; 170 } 171 172 static int jent_kcapi_reset(struct crypto_rng *tfm, 173 const u8 *seed, unsigned int slen) 174 { 175 return 0; 176 } 177 178 static struct rng_alg jent_alg = { 179 .generate = jent_kcapi_random, 180 .seed = jent_kcapi_reset, 181 .seedsize = 0, 182 .base = { 183 .cra_name = "jitterentropy_rng", 184 .cra_driver_name = "jitterentropy_rng", 185 .cra_priority = 100, 186 .cra_ctxsize = sizeof(struct jitterentropy), 187 .cra_module = THIS_MODULE, 188 .cra_init = jent_kcapi_init, 189 .cra_exit = jent_kcapi_cleanup, 190 191 } 192 }; 193 194 static int __init jent_mod_init(void) 195 { 196 int ret = 0; 197 198 ret = jent_entropy_init(); 199 if (ret) { 200 pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); 201 return -EFAULT; 202 } 203 return crypto_register_rng(&jent_alg); 204 } 205 206 static void __exit jent_mod_exit(void) 207 { 208 crypto_unregister_rng(&jent_alg); 209 } 210 211 module_init(jent_mod_init); 212 module_exit(jent_mod_exit); 213 214 MODULE_LICENSE("Dual BSD/GPL"); 215 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 216 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter"); 217 MODULE_ALIAS_CRYPTO("jitterentropy_rng"); 218