/*
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* Non-physical true random number generator based on timing jitter --
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* Linux Kernel Crypto API specific code
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*
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* Copyright Stephan Mueller <smueller@chronox.de>, 2015
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, and the entire permission notice in its entirety,
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* including the disclaimer of warranties.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote
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* products derived from this software without specific prior
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* written permission.
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*
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* ALTERNATIVELY, this product may be distributed under the terms of
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* the GNU General Public License, in which case the provisions of the GPL2 are
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* required INSTEAD OF the above restrictions. (This clause is
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* necessary due to a potential bad interaction between the GPL and
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* the restrictions contained in a BSD-style copyright.)
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
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* WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
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* OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
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* USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/fips.h>
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#include <linux/time.h>
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#include <crypto/internal/rng.h>
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#include "jitterentropy.h"
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/***************************************************************************
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* Helper function
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***************************************************************************/
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void *jent_zalloc(unsigned int len)
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{
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return kzalloc(len, GFP_KERNEL);
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}
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void jent_zfree(void *ptr)
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{
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kfree_sensitive(ptr);
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}
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int jent_fips_enabled(void)
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{
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return fips_enabled;
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}
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void jent_panic(char *s)
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{
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panic("%s", s);
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}
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void jent_memcpy(void *dest, const void *src, unsigned int n)
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{
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memcpy(dest, src, n);
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}
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/*
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* Obtain a high-resolution time stamp value. The time stamp is used to measure
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* the execution time of a given code path and its variations. Hence, the time
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* stamp must have a sufficiently high resolution.
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*
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* Note, if the function returns zero because a given architecture does not
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* implement a high-resolution time stamp, the RNG code's runtime test
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* will detect it and will not produce output.
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*/
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void jent_get_nstime(__u64 *out)
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{
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__u64 tmp = 0;
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tmp = random_get_entropy();
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/*
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* If random_get_entropy does not return a value, i.e. it is not
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* implemented for a given architecture, use a clock source.
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* hoping that there are timers we can work with.
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*/
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if (tmp == 0)
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tmp = ktime_get_ns();
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*out = tmp;
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}
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/***************************************************************************
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* Kernel crypto API interface
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***************************************************************************/
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struct jitterentropy {
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spinlock_t jent_lock;
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struct rand_data *entropy_collector;
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unsigned int reset_cnt;
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};
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static int jent_kcapi_init(struct crypto_tfm *tfm)
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{
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struct jitterentropy *rng = crypto_tfm_ctx(tfm);
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int ret = 0;
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rng->entropy_collector = jent_entropy_collector_alloc(1, 0);
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if (!rng->entropy_collector)
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ret = -ENOMEM;
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spin_lock_init(&rng->jent_lock);
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return ret;
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}
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static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
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{
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struct jitterentropy *rng = crypto_tfm_ctx(tfm);
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spin_lock(&rng->jent_lock);
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if (rng->entropy_collector)
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jent_entropy_collector_free(rng->entropy_collector);
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rng->entropy_collector = NULL;
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spin_unlock(&rng->jent_lock);
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}
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static int jent_kcapi_random(struct crypto_rng *tfm,
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const u8 *src, unsigned int slen,
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u8 *rdata, unsigned int dlen)
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{
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struct jitterentropy *rng = crypto_rng_ctx(tfm);
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int ret = 0;
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spin_lock(&rng->jent_lock);
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/* Return a permanent error in case we had too many resets in a row. */
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if (rng->reset_cnt > (1<<10)) {
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ret = -EFAULT;
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goto out;
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}
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ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
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/* Reset RNG in case of health failures */
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if (ret < -1) {
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pr_warn_ratelimited("Reset Jitter RNG due to health test failure: %s failure\n",
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(ret == -2) ? "Repetition Count Test" :
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"Adaptive Proportion Test");
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rng->reset_cnt++;
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ret = -EAGAIN;
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} else {
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rng->reset_cnt = 0;
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/* Convert the Jitter RNG error into a usable error code */
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if (ret == -1)
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ret = -EINVAL;
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}
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out:
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spin_unlock(&rng->jent_lock);
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return ret;
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}
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static int jent_kcapi_reset(struct crypto_rng *tfm,
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const u8 *seed, unsigned int slen)
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{
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return 0;
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}
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static struct rng_alg jent_alg = {
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.generate = jent_kcapi_random,
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.seed = jent_kcapi_reset,
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.seedsize = 0,
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.base = {
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.cra_name = "jitterentropy_rng",
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.cra_driver_name = "jitterentropy_rng",
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.cra_priority = 100,
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.cra_ctxsize = sizeof(struct jitterentropy),
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.cra_module = THIS_MODULE,
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.cra_init = jent_kcapi_init,
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.cra_exit = jent_kcapi_cleanup,
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}
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};
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static int __init jent_mod_init(void)
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{
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int ret = 0;
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ret = jent_entropy_init();
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if (ret) {
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pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
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return -EFAULT;
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}
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return crypto_register_rng(&jent_alg);
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}
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static void __exit jent_mod_exit(void)
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{
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crypto_unregister_rng(&jent_alg);
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}
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module_init(jent_mod_init);
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module_exit(jent_mod_exit);
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MODULE_LICENSE("Dual BSD/GPL");
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MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
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MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
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MODULE_ALIAS_CRYPTO("jitterentropy_rng");
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