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![Stephan Müller](/assets/img/avatar_default.png)
The test interface allows a privileged process to capture the raw unconditioned noise that is collected by the Jitter RNG for statistical analysis. Such testing allows the analysis how much entropy the Jitter RNG noise source provides on a given platform. The obtained data is the time stamp sampled by the Jitter RNG. Considering that the Jitter RNG inserts the delta of this time stamp compared to the immediately preceding time stamp, the obtained data needs to be post-processed accordingly to obtain the data the Jitter RNG inserts into its entropy pool. The raw entropy collection is provided to obtain the raw unmodified time stamps that are about to be added to the Jitter RNG entropy pool and are credited with entropy. Thus, this patch adds an interface which renders the Jitter RNG insecure. This patch is NOT INTENDED FOR PRODUCTION SYSTEMS, but solely for development/test systems to verify the available entropy rate. Access to the data is given through the jent_raw_hires debugfs file. The data buffer should be multiples of sizeof(u32) to fill the entire buffer. Using the option jitterentropy_testing.boot_raw_hires_test=1 the raw noise of the first 1000 entropy events since boot can be sampled. This test interface allows generating the data required for analysis whether the Jitter RNG is in compliance with SP800-90B sections 3.1.3 and 3.1.4. If the test interface is not compiled, its code is a noop which has no impact on the performance. Signed-off-by: Stephan Mueller <smueller@chronox.de> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
364 lines
11 KiB
C
364 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_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 = jent_entropy_collector_alloc(1, 0, 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(desc);
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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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