linux/crypto/jitterentropy-kcapi.c
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   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
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