378 lines
11 KiB
C
378 lines
11 KiB
C
/*
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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 - 2023
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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 <crypto/hash.h>
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#include <crypto/sha3.h>
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#include <linux/fips.h>
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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/time.h>
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#include <crypto/internal/rng.h>
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#include "jitterentropy.h"
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#define JENT_CONDITIONING_HASH "sha3-256-generic"
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/***************************************************************************
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* Helper function
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***************************************************************************/
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void *jent_kvzalloc(unsigned int len)
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{
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return kvzalloc(len, GFP_KERNEL);
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}
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void jent_kvzfree(void *ptr, unsigned int len)
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{
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memzero_explicit(ptr, len);
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kvfree(ptr);
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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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/*
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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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jent_raw_hires_entropy_store(tmp);
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}
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int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
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unsigned int addtl_len, __u64 hash_loop_cnt,
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unsigned int stuck)
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{
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struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
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SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm);
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u8 intermediary[SHA3_256_DIGEST_SIZE];
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__u64 j = 0;
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int ret;
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desc->tfm = hash_state_desc->tfm;
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if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) {
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pr_warn_ratelimited("Unexpected digest size\n");
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return -EINVAL;
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}
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/*
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* This loop fills a buffer which is injected into the entropy pool.
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* The main reason for this loop is to execute something over which we
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* can perform a timing measurement. The injection of the resulting
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* data into the pool is performed to ensure the result is used and
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* the compiler cannot optimize the loop away in case the result is not
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* used at all. Yet that data is considered "additional information"
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* considering the terminology from SP800-90A without any entropy.
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*
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* Note, it does not matter which or how much data you inject, we are
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* interested in one Keccack1600 compression operation performed with
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* the crypto_shash_final.
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*/
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for (j = 0; j < hash_loop_cnt; j++) {
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ret = crypto_shash_init(desc) ?:
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crypto_shash_update(desc, intermediary,
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sizeof(intermediary)) ?:
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crypto_shash_finup(desc, addtl, addtl_len, intermediary);
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if (ret)
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goto err;
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}
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/*
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* Inject the data from the previous loop into the pool. This data is
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* not considered to contain any entropy, but it stirs the pool a bit.
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*/
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ret = crypto_shash_update(desc, intermediary, sizeof(intermediary));
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if (ret)
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goto err;
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/*
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* Insert the time stamp into the hash context representing the pool.
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*
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* If the time stamp is stuck, do not finally insert the value into the
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* entropy pool. Although this operation should not do any harm even
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* when the time stamp has no entropy, SP800-90B requires that any
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* conditioning operation to have an identical amount of input data
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* according to section 3.1.5.
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*/
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if (!stuck) {
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ret = crypto_shash_update(hash_state_desc, (u8 *)&time,
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sizeof(__u64));
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}
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err:
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shash_desc_zero(desc);
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memzero_explicit(intermediary, sizeof(intermediary));
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return ret;
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}
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int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len)
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{
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struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
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u8 jent_block[SHA3_256_DIGEST_SIZE];
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/* Obtain data from entropy pool and re-initialize it */
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int ret = crypto_shash_final(hash_state_desc, jent_block) ?:
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crypto_shash_init(hash_state_desc) ?:
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crypto_shash_update(hash_state_desc, jent_block,
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sizeof(jent_block));
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if (!ret && dst_len)
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memcpy(dst, jent_block, dst_len);
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memzero_explicit(jent_block, sizeof(jent_block));
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return ret;
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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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struct crypto_shash *tfm;
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struct shash_desc *sdesc;
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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->sdesc) {
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shash_desc_zero(rng->sdesc);
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kfree(rng->sdesc);
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}
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rng->sdesc = NULL;
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if (rng->tfm)
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crypto_free_shash(rng->tfm);
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rng->tfm = NULL;
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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_init(struct crypto_tfm *tfm)
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{
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struct jitterentropy *rng = crypto_tfm_ctx(tfm);
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struct crypto_shash *hash;
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struct shash_desc *sdesc;
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int size, ret = 0;
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spin_lock_init(&rng->jent_lock);
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/*
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* Use SHA3-256 as conditioner. We allocate only the generic
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* implementation as we are not interested in high-performance. The
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* execution time of the SHA3 operation is measured and adds to the
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* Jitter RNG's unpredictable behavior. If we have a slower hash
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* implementation, the execution timing variations are larger. When
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* using a fast implementation, we would need to call it more often
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* as its variations are lower.
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*/
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hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
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if (IS_ERR(hash)) {
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pr_err("Cannot allocate conditioning digest\n");
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return PTR_ERR(hash);
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}
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rng->tfm = hash;
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size = sizeof(struct shash_desc) + crypto_shash_descsize(hash);
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sdesc = kmalloc(size, GFP_KERNEL);
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if (!sdesc) {
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ret = -ENOMEM;
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goto err;
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}
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sdesc->tfm = hash;
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crypto_shash_init(sdesc);
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rng->sdesc = sdesc;
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rng->entropy_collector =
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jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0,
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sdesc);
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if (!rng->entropy_collector) {
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ret = -ENOMEM;
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goto err;
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}
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spin_lock_init(&rng->jent_lock);
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return 0;
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err:
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jent_kcapi_cleanup(tfm);
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return ret;
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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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ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
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if (ret == -3) {
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/* Handle permanent health test error */
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/*
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* If the kernel was booted with fips=1, it implies that
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* the entire kernel acts as a FIPS 140 module. In this case
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* an SP800-90B permanent health test error is treated as
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* a FIPS module error.
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*/
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if (fips_enabled)
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panic("Jitter RNG permanent health test failure\n");
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pr_err("Jitter RNG permanent health test failure\n");
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ret = -EFAULT;
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} else if (ret == -2) {
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/* Handle intermittent health test error */
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pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n");
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ret = -EAGAIN;
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} else if (ret == -1) {
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/* Handle other errors */
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ret = -EINVAL;
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}
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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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SHASH_DESC_ON_STACK(desc, tfm);
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struct crypto_shash *tfm;
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int ret = 0;
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jent_testing_init();
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tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
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if (IS_ERR(tfm)) {
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jent_testing_exit();
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return PTR_ERR(tfm);
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}
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desc->tfm = tfm;
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crypto_shash_init(desc);
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ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc, NULL);
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shash_desc_zero(desc);
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crypto_free_shash(tfm);
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if (ret) {
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/* Handle permanent health test error */
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if (fips_enabled)
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panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
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jent_testing_exit();
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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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jent_testing_exit();
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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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