crypto/jitterentropy-kcapi.c

   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
  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");