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/fips.h> 41 #include <linux/kernel.h> 42 #include <linux/module.h> 43 #include <linux/slab.h> 44 #include <linux/time.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 void jent_memcpy(void *dest, const void *src, unsigned int n) 64 { 65 memcpy(dest, src, n); 66 } 67 68 /* 69 * Obtain a high-resolution time stamp value. The time stamp is used to measure 70 * the execution time of a given code path and its variations. Hence, the time 71 * stamp must have a sufficiently high resolution. 72 * 73 * Note, if the function returns zero because a given architecture does not 74 * implement a high-resolution time stamp, the RNG code's runtime test 75 * will detect it and will not produce output. 76 */ 77 void jent_get_nstime(__u64 *out) 78 { 79 __u64 tmp = 0; 80 81 tmp = random_get_entropy(); 82 83 /* 84 * If random_get_entropy does not return a value, i.e. it is not 85 * implemented for a given architecture, use a clock source. 86 * hoping that there are timers we can work with. 87 */ 88 if (tmp == 0) 89 tmp = ktime_get_ns(); 90 91 *out = tmp; 92 } 93 94 /*************************************************************************** 95 * Kernel crypto API interface 96 ***************************************************************************/ 97 98 struct jitterentropy { 99 spinlock_t jent_lock; 100 struct rand_data *entropy_collector; 101 }; 102 103 static int jent_kcapi_init(struct crypto_tfm *tfm) 104 { 105 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 106 int ret = 0; 107 108 rng->entropy_collector = jent_entropy_collector_alloc(1, 0); 109 if (!rng->entropy_collector) 110 ret = -ENOMEM; 111 112 spin_lock_init(&rng->jent_lock); 113 return ret; 114 } 115 116 static void jent_kcapi_cleanup(struct crypto_tfm *tfm) 117 { 118 struct jitterentropy *rng = crypto_tfm_ctx(tfm); 119 120 spin_lock(&rng->jent_lock); 121 if (rng->entropy_collector) 122 jent_entropy_collector_free(rng->entropy_collector); 123 rng->entropy_collector = NULL; 124 spin_unlock(&rng->jent_lock); 125 } 126 127 static int jent_kcapi_random(struct crypto_rng *tfm, 128 const u8 *src, unsigned int slen, 129 u8 *rdata, unsigned int dlen) 130 { 131 struct jitterentropy *rng = crypto_rng_ctx(tfm); 132 int ret = 0; 133 134 spin_lock(&rng->jent_lock); 135 136 ret = jent_read_entropy(rng->entropy_collector, rdata, dlen); 137 138 if (ret == -3) { 139 /* Handle permanent health test error */ 140 /* 141 * If the kernel was booted with fips=1, it implies that 142 * the entire kernel acts as a FIPS 140 module. In this case 143 * an SP800-90B permanent health test error is treated as 144 * a FIPS module error. 145 */ 146 if (fips_enabled) 147 panic("Jitter RNG permanent health test failure\n"); 148 149 pr_err("Jitter RNG permanent health test failure\n"); 150 ret = -EFAULT; 151 } else if (ret == -2) { 152 /* Handle intermittent health test error */ 153 pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n"); 154 ret = -EAGAIN; 155 } else if (ret == -1) { 156 /* Handle other errors */ 157 ret = -EINVAL; 158 } 159 160 spin_unlock(&rng->jent_lock); 161 162 return ret; 163 } 164 165 static int jent_kcapi_reset(struct crypto_rng *tfm, 166 const u8 *seed, unsigned int slen) 167 { 168 return 0; 169 } 170 171 static struct rng_alg jent_alg = { 172 .generate = jent_kcapi_random, 173 .seed = jent_kcapi_reset, 174 .seedsize = 0, 175 .base = { 176 .cra_name = "jitterentropy_rng", 177 .cra_driver_name = "jitterentropy_rng", 178 .cra_priority = 100, 179 .cra_ctxsize = sizeof(struct jitterentropy), 180 .cra_module = THIS_MODULE, 181 .cra_init = jent_kcapi_init, 182 .cra_exit = jent_kcapi_cleanup, 183 184 } 185 }; 186 187 static int __init jent_mod_init(void) 188 { 189 int ret = 0; 190 191 ret = jent_entropy_init(); 192 if (ret) { 193 /* Handle permanent health test error */ 194 if (fips_enabled) 195 panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); 196 197 pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret); 198 return -EFAULT; 199 } 200 return crypto_register_rng(&jent_alg); 201 } 202 203 static void __exit jent_mod_exit(void) 204 { 205 crypto_unregister_rng(&jent_alg); 206 } 207 208 module_init(jent_mod_init); 209 module_exit(jent_mod_exit); 210 211 MODULE_LICENSE("Dual BSD/GPL"); 212 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 213 MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter"); 214 MODULE_ALIAS_CRYPTO("jitterentropy_rng"); 215