/*
* Non-physical true random number generator based on timing jitter --
* Linux Kernel Crypto API specific code
*
* Copyright Stephan Mueller <[email protected]>, 2015 - 2023
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, and the entire permission notice in its entirety,
* including the disclaimer of warranties.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* ALTERNATIVELY, this product may be distributed under the terms of
* the GNU General Public License, in which case the provisions of the GPL2 are
* required INSTEAD OF the above restrictions. (This clause is
* necessary due to a potential bad interaction between the GPL and
* the restrictions contained in a BSD-style copyright.)
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
* WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
* OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
* USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*/
#include <crypto/hash.h>
#include <crypto/sha3.h>
#include <linux/fips.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <crypto/internal/rng.h>
#include "jitterentropy.h"
#define JENT_CONDITIONING_HASH "sha3-256-generic"
/***************************************************************************
* Helper function
***************************************************************************/
void *jent_kvzalloc(unsigned int len)
{
return kvzalloc(len, GFP_KERNEL);
}
void jent_kvzfree(void *ptr, unsigned int len)
{
kvfree_sensitive(ptr, len);
}
void *jent_zalloc(unsigned int len)
{
return kzalloc(len, GFP_KERNEL);
}
void jent_zfree(void *ptr)
{
kfree_sensitive(ptr);
}
/*
* Obtain a high-resolution time stamp value. The time stamp is used to measure
* the execution time of a given code path and its variations. Hence, the time
* stamp must have a sufficiently high resolution.
*
* Note, if the function returns zero because a given architecture does not
* implement a high-resolution time stamp, the RNG code's runtime test
* will detect it and will not produce output.
*/
void jent_get_nstime(__u64 *out)
{
__u64 tmp = 0;
tmp = random_get_entropy();
/*
* If random_get_entropy does not return a value, i.e. it is not
* implemented for a given architecture, use a clock source.
* hoping that there are timers we can work with.
*/
if (tmp == 0)
tmp = ktime_get_ns();
*out = tmp;
jent_raw_hires_entropy_store(tmp);
}
int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
unsigned int addtl_len, __u64 hash_loop_cnt,
unsigned int stuck)
{
struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm);
u8 intermediary[SHA3_256_DIGEST_SIZE];
__u64 j = 0;
int ret;
desc->tfm = hash_state_desc->tfm;
if (sizeof(intermediary) != crypto_shash_digestsize(desc->tfm)) {
pr_warn_ratelimited("Unexpected digest size\n");
return -EINVAL;
}
/*
* This loop fills a buffer which is injected into the entropy pool.
* The main reason for this loop is to execute something over which we
* can perform a timing measurement. The injection of the resulting
* data into the pool is performed to ensure the result is used and
* the compiler cannot optimize the loop away in case the result is not
* used at all. Yet that data is considered "additional information"
* considering the terminology from SP800-90A without any entropy.
*
* Note, it does not matter which or how much data you inject, we are
* interested in one Keccack1600 compression operation performed with
* the crypto_shash_final.
*/
for (j = 0; j < hash_loop_cnt; j++) {
ret = crypto_shash_init(desc) ?:
crypto_shash_update(desc, intermediary,
sizeof(intermediary)) ?:
crypto_shash_finup(desc, addtl, addtl_len, intermediary);
if (ret)
goto err;
}
/*
* Inject the data from the previous loop into the pool. This data is
* not considered to contain any entropy, but it stirs the pool a bit.
*/
ret = crypto_shash_update(desc, intermediary, sizeof(intermediary));
if (ret)
goto err;
/*
* Insert the time stamp into the hash context representing the pool.
*
* If the time stamp is stuck, do not finally insert the value into the
* entropy pool. Although this operation should not do any harm even
* when the time stamp has no entropy, SP800-90B requires that any
* conditioning operation to have an identical amount of input data
* according to section 3.1.5.
*/
if (!stuck) {
ret = crypto_shash_update(hash_state_desc, (u8 *)&time,
sizeof(__u64));
}
err:
shash_desc_zero(desc);
memzero_explicit(intermediary, sizeof(intermediary));
return ret;
}
int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len)
{
struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
u8 jent_block[SHA3_256_DIGEST_SIZE];
/* Obtain data from entropy pool and re-initialize it */
int ret = crypto_shash_final(hash_state_desc, jent_block) ?:
crypto_shash_init(hash_state_desc) ?:
crypto_shash_update(hash_state_desc, jent_block,
sizeof(jent_block));
if (!ret && dst_len)
memcpy(dst, jent_block, dst_len);
memzero_explicit(jent_block, sizeof(jent_block));
return ret;
}
/***************************************************************************
* Kernel crypto API interface
***************************************************************************/
struct jitterentropy {
spinlock_t jent_lock;
struct rand_data *entropy_collector;
struct crypto_shash *tfm;
struct shash_desc *sdesc;
};
static void jent_kcapi_cleanup(struct crypto_tfm *tfm)
{
struct jitterentropy *rng = crypto_tfm_ctx(tfm);
spin_lock(&rng->jent_lock);
if (rng->sdesc) {
shash_desc_zero(rng->sdesc);
kfree(rng->sdesc);
}
rng->sdesc = NULL;
if (rng->tfm)
crypto_free_shash(rng->tfm);
rng->tfm = NULL;
if (rng->entropy_collector)
jent_entropy_collector_free(rng->entropy_collector);
rng->entropy_collector = NULL;
spin_unlock(&rng->jent_lock);
}
static int jent_kcapi_init(struct crypto_tfm *tfm)
{
struct jitterentropy *rng = crypto_tfm_ctx(tfm);
struct crypto_shash *hash;
struct shash_desc *sdesc;
int size, ret = 0;
spin_lock_init(&rng->jent_lock);
/*
* Use SHA3-256 as conditioner. We allocate only the generic
* implementation as we are not interested in high-performance. The
* execution time of the SHA3 operation is measured and adds to the
* Jitter RNG's unpredictable behavior. If we have a slower hash
* implementation, the execution timing variations are larger. When
* using a fast implementation, we would need to call it more often
* as its variations are lower.
*/
hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
if (IS_ERR(hash)) {
pr_err("Cannot allocate conditioning digest\n");
return PTR_ERR(hash);
}
rng->tfm = hash;
size = sizeof(struct shash_desc) + crypto_shash_descsize(hash);
sdesc = kmalloc(size, GFP_KERNEL);
if (!sdesc) {
ret = -ENOMEM;
goto err;
}
sdesc->tfm = hash;
crypto_shash_init(sdesc);
rng->sdesc = sdesc;
rng->entropy_collector =
jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0,
sdesc);
if (!rng->entropy_collector) {
ret = -ENOMEM;
goto err;
}
spin_lock_init(&rng->jent_lock);
return 0;
err:
jent_kcapi_cleanup(tfm);
return ret;
}
static int jent_kcapi_random(struct crypto_rng *tfm,
const u8 *src, unsigned int slen,
u8 *rdata, unsigned int dlen)
{
struct jitterentropy *rng = crypto_rng_ctx(tfm);
int ret = 0;
spin_lock(&rng->jent_lock);
ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
if (ret == -3) {
/* Handle permanent health test error */
/*
* If the kernel was booted with fips=1, it implies that
* the entire kernel acts as a FIPS 140 module. In this case
* an SP800-90B permanent health test error is treated as
* a FIPS module error.
*/
if (fips_enabled)
panic("Jitter RNG permanent health test failure\n");
pr_err("Jitter RNG permanent health test failure\n");
ret = -EFAULT;
} else if (ret == -2) {
/* Handle intermittent health test error */
pr_warn_ratelimited("Reset Jitter RNG due to intermittent health test failure\n");
ret = -EAGAIN;
} else if (ret == -1) {
/* Handle other errors */
ret = -EINVAL;
}
spin_unlock(&rng->jent_lock);
return ret;
}
static int jent_kcapi_reset(struct crypto_rng *tfm,
const u8 *seed, unsigned int slen)
{
return 0;
}
static struct rng_alg jent_alg = {
.generate = jent_kcapi_random,
.seed = jent_kcapi_reset,
.seedsize = 0,
.base = {
.cra_name = "jitterentropy_rng",
.cra_driver_name = "jitterentropy_rng",
.cra_priority = 100,
.cra_ctxsize = sizeof(struct jitterentropy),
.cra_module = THIS_MODULE,
.cra_init = jent_kcapi_init,
.cra_exit = jent_kcapi_cleanup,
}
};
static int __init jent_mod_init(void)
{
SHASH_DESC_ON_STACK(desc, tfm);
struct crypto_shash *tfm;
int ret = 0;
jent_testing_init();
tfm = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
if (IS_ERR(tfm)) {
jent_testing_exit();
return PTR_ERR(tfm);
}
desc->tfm = tfm;
crypto_shash_init(desc);
ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc, NULL);
shash_desc_zero(desc);
crypto_free_shash(tfm);
if (ret) {
/* Handle permanent health test error */
if (fips_enabled)
panic("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
jent_testing_exit();
pr_info("jitterentropy: Initialization failed with host not compliant with requirements: %d\n", ret);
return -EFAULT;
}
return crypto_register_rng(&jent_alg);
}
static void __exit jent_mod_exit(void)
{
jent_testing_exit();
crypto_unregister_rng(&jent_alg);
}
module_init(jent_mod_init);
module_exit(jent_mod_exit);
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Stephan Mueller <[email protected]>");
MODULE_DESCRIPTION("Non-physical True Random Number Generator based on CPU Jitter");
MODULE_ALIAS_CRYPTO("jitterentropy_rng");
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