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incubator-nuttx/crypto/random_pool.c

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/****************************************************************************
* crypto/random_pool.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <debug.h>
#include <assert.h>
#include <errno.h>
#include <nuttx/random.h>
#include <nuttx/board.h>
#include <nuttx/clock.h>
#include <nuttx/semaphore.h>
#include <nuttx/crypto/blake2s.h>
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#ifndef MIN
# define MIN(a,b) ((a) < (b) ? (a) : (b))
#endif
#define ROTL_32(x,n) ( ((x) << (n)) | ((x) >> (32-(n))) )
#define ROTR_32(x,n) ( ((x) >> (n)) | ((x) << (32-(n))) )
/****************************************************************************
* Private Function Prototypes
****************************************************************************/
/****************************************************************************
* Private Types
****************************************************************************/
struct blake2xs_rng_s
{
uint32_t out_node_offset;
blake2s_param param;
blake2s_state ctx;
char out_root[BLAKE2S_OUTBYTES];
};
struct rng_s
{
sem_t rd_sem; /* Threads can only exclusively access the RNG */
volatile uint32_t rd_addptr;
volatile uint32_t rd_newentr;
volatile uint8_t rd_rotate;
volatile uint8_t rd_prev_time;
volatile uint16_t rd_prev_irq;
bool output_initialized;
struct blake2xs_rng_s blake2xs;
};
enum
{
POOL_SIZE = ENTROPY_POOL_SIZE,
POOL_MASK = (POOL_SIZE - 1),
MIN_SEED_NEW_ENTROPY_WORDS = 128,
MAX_SEED_NEW_ENTROPY_WORDS = 1024
};
/****************************************************************************
* Private Data
****************************************************************************/
static struct rng_s g_rng;
#ifdef CONFIG_BOARD_ENTROPY_POOL
/* Entropy pool structure can be provided by board source. Use for this is,
* for example, allocate entropy pool from special area of RAM which content
* is kept over system reset.
*/
# define entropy_pool board_entropy_pool
#else
static struct entropy_pool_s entropy_pool;
#endif
/* Polynomial from paper "The Linux Pseudorandom Number Generator Revisited"
* x^POOL_SIZE + x^104 + x^76 + x^51 + x^25 + x + 1
*/
static const uint32_t pool_stir[] =
{
POOL_SIZE, 104, 76, 51, 25, 1
};
/* Derived from IEEE 802.3 CRC-32 */
static const uint32_t pool_twist[8] =
{
0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278
};
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: addentropy
*
* Description:
*
* This function adds a number of integers into the entropy pool.
* The pool is stirred with a polynomial of degree POOL_SIZE over GF(2).
*
* Code is inspired by add_entropy_words() function of OpenBSD kernel.
*
* Input Parameters:
* buf - Buffer of integers to be added
* n - Number of elements in buf
* inc_new - Count element as new entry
*
* Returned Value:
* None
*
****************************************************************************/
static void addentropy(FAR const uint32_t *buf, size_t n, bool inc_new)
{
/* Compile time check for that POOL_SIZE is power of two. */
static char pool_size_p2_check[1 - ((POOL_SIZE & (POOL_SIZE - 1)) * 2)];
UNUSED(pool_size_p2_check);
while (n-- > 0)
{
uint32_t rotate;
uint32_t w;
uint32_t i;
rotate = g_rng.rd_rotate;
w = rotate ? ROTL_32(*buf, rotate) : *buf;
i = g_rng.rd_addptr = (g_rng.rd_addptr - 1) & POOL_MASK;
/* Normal round, we add 7 bits of rotation to the pool.
* At the beginning of the pool, we add extra 7 bits
* rotation, in order for successive passes spread the
* input bits across the pool evenly.
*/
g_rng.rd_rotate = (rotate + (i ? 7 : 14)) & 31;
/* XOR pool contents corresponding to polynomial terms */
w ^= entropy_pool.pool[(i + pool_stir[1]) & POOL_MASK];
w ^= entropy_pool.pool[(i + pool_stir[2]) & POOL_MASK];
w ^= entropy_pool.pool[(i + pool_stir[3]) & POOL_MASK];
w ^= entropy_pool.pool[(i + pool_stir[4]) & POOL_MASK];
w ^= entropy_pool.pool[(i + pool_stir[5]) & POOL_MASK];
w ^= entropy_pool.pool[i]; /* 2^POOL_SIZE */
entropy_pool.pool[i] = (w >> 3) ^ pool_twist[w & 7];
buf++;
if (inc_new)
{
g_rng.rd_newentr += 1;
}
}
}
/****************************************************************************
* Name: getentropy
*
* Description:
* Hash entropy pool to BLAKE2s context. This is an internal interface for
* seeding out-facing BLAKE2Xs random bit generator from entropy pool.
*
* Code is inspired by extract_entropy() function of OpenBSD kernel.
*
* Note that this function cannot fail, other than by asserting.
*
* Warning: In protected kernel builds, this interface MUST NOT be
* exported to userspace. This interface MUST NOT be used as a
* general-purpose random bit generator!
*
* Input Parameters:
* S - BLAKE2s instance that will absorb entropy pool
*
* Returned Value:
* None
*
****************************************************************************/
static void getentropy(FAR blake2s_state *S)
{
#ifdef CONFIG_SCHED_CPULOAD
struct cpuload_s load;
#endif
uint32_t tmp;
add_sw_randomness(g_rng.rd_newentr);
/* Absorb the entropy pool */
blake2s_update(S, (FAR const uint32_t *)entropy_pool.pool,
sizeof(entropy_pool.pool));
/* Add something back so repeated calls to this function
* return different values.
*/
tmp = sizeof(entropy_pool.pool);
tmp <<= 27;
#ifdef CONFIG_SCHED_CPULOAD
clock_cpuload(0, &load);
tmp += load.total ^ ROTL_32(load.active, 23);
#endif
add_sw_randomness(tmp);
g_rng.rd_newentr = 0;
}
/* The BLAKE2Xs based random number generator algorithm.
*
* BLAKE2X is a extensible-output function (XOF) variant of BLAKE2 hash
* function. One application of XOFs is use as deterministic random bit
* number generator (DRBG) as used here. BLAKE2 specification is available
* at https://blake2.net/
*
* BLAKE2Xs here implementation is based on public-domain/CC0 BLAKE2
* reference implementation by Samual Neves, at
*
* https://github.com/BLAKE2/BLAKE2/tree/master/ref
* Copyright 2012, Samuel Neves <sneves@dei.uc.pt>
*/
static void rng_reseed(void)
{
blake2s_param P =
{
};
/* Reset output node counter. */
g_rng.blake2xs.out_node_offset = 0;
/* Initialize parameter block */
P.digest_length = BLAKE2S_OUTBYTES;
P.key_length = 0;
P.fanout = 1;
P.depth = 1;
blake2_store32(P.leaf_length, 0);
blake2_store32(P.node_offset, 0);
blake2_store16(P.xof_length, 0xffff);
P.node_depth = 0;
P.inner_length = 0;
g_rng.blake2xs.param = P;
blake2s_init_param(&g_rng.blake2xs.ctx, &g_rng.blake2xs.param);
/* Initialize with randomness from entropy pool */
getentropy(&g_rng.blake2xs.ctx);
/* Absorb also the previous root */
blake2s_update(&g_rng.blake2xs.ctx, g_rng.blake2xs.out_root,
sizeof(g_rng.blake2xs.out_root));
/* Finalize the new root hash */
blake2s_final(&g_rng.blake2xs.ctx, g_rng.blake2xs.out_root,
BLAKE2S_OUTBYTES);
explicit_bzero(&g_rng.blake2xs.ctx, sizeof(g_rng.blake2xs.ctx));
/* Setup parameters for output phase. */
g_rng.blake2xs.param.key_length = 0;
g_rng.blake2xs.param.fanout = 0;
blake2_store32(g_rng.blake2xs.param.leaf_length, BLAKE2S_OUTBYTES);
g_rng.blake2xs.param.inner_length = BLAKE2S_OUTBYTES;
g_rng.blake2xs.param.node_depth = 0;
g_rng.output_initialized = true;
}
static void rng_buf_internal(FAR uint8_t *bytes, size_t nbytes)
{
if (!g_rng.output_initialized)
{
if (g_rng.rd_newentr < MIN_SEED_NEW_ENTROPY_WORDS)
{
cryptwarn("Entropy pool RNG initialized with very low entropy. "
" Consider implementing CONFIG_BOARD_INITRNGSEED!\n");
}
rng_reseed();
}
else if (g_rng.rd_newentr >= MAX_SEED_NEW_ENTROPY_WORDS)
{
/* Initial entropy is low. Reseed when we have accumulated more. */
rng_reseed();
}
else if (g_rng.blake2xs.out_node_offset == UINT32_MAX)
{
/* Maximum BLAKE2Xs output reached (2^32-1 output blocks, maximum 128
* GiB bytes), reseed.
*/
rng_reseed();
}
/* Output phase for BLAKE2Xs. */
for (; nbytes > 0; ++g_rng.blake2xs.out_node_offset)
{
size_t block_size = MIN(nbytes, BLAKE2S_OUTBYTES);
/* Initialize state */
g_rng.blake2xs.param.digest_length = block_size;
blake2_store32(g_rng.blake2xs.param.node_offset,
g_rng.blake2xs.out_node_offset);
blake2s_init_param(&g_rng.blake2xs.ctx, &g_rng.blake2xs.param);
/* Process state and output random bytes */
blake2s_update(&g_rng.blake2xs.ctx, g_rng.blake2xs.out_root,
sizeof(g_rng.blake2xs.out_root));
blake2s_final(&g_rng.blake2xs.ctx, bytes, block_size);
bytes += block_size;
nbytes -= block_size;
}
}
static void rng_init(void)
{
cryptinfo("Initializing RNG\n");
memset(&g_rng, 0, sizeof(struct rng_s));
nxsem_init(&g_rng.rd_sem, 0, 1);
/* We do not initialize output here because this is called
* quite early in boot and there may not be enough entropy.
*
* Board level may define CONFIG_BOARD_INITRNGSEED if it implements
* early random seeding.
*/
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: up_rngaddint
*
* Description:
* Add one integer to entropy pool, contributing a specific kind
* of entropy to pool.
*
* Input Parameters:
* kindof - Enumeration constant telling where val came from
* val - Integer to be added
*
* Returned Value:
* None
*
****************************************************************************/
void up_rngaddint(enum rnd_source_t kindof, int val)
{
uint32_t buf[1];
buf[0] = val;
up_rngaddentropy(kindof, buf, 1);
}
/****************************************************************************
* Name: up_rngaddentropy
*
* Description:
* Add buffer of integers to entropy pool.
*
* Input Parameters:
* kindof - Enumeration constant telling where val came from
* buf - Buffer of integers to be added
* n - Number of elements in buf
*
* Returned Value:
* None
*
****************************************************************************/
void up_rngaddentropy(enum rnd_source_t kindof, FAR const uint32_t *buf,
size_t n)
{
uint32_t tbuf[1];
struct timespec ts;
bool new_inc = true;
if (kindof == RND_SRC_IRQ && n > 0)
{
/* Ignore interrupt randomness if previous interrupt was from same
* source.
*/
if (buf[0] == g_rng.rd_prev_irq)
{
return;
}
g_rng.rd_prev_irq = buf[0];
}
/* We don't actually track what kind of entropy we receive,
* just add it all to pool. One exception is interrupt
* and timer randomness, where we limit rate of new pool entry
* counting to prevent high interrupt rate triggering RNG
* reseeding too fast.
*/
clock_systime_timespec(&ts);
tbuf[0] = ROTL_32((uint32_t)ts.tv_nsec, 17) ^ ROTL_32(ts.tv_sec, 3);
tbuf[0] += ROTL_32(kindof, 27);
tbuf[0] += ROTL_32((uintptr_t)&tbuf[0], 11);
if (kindof == RND_SRC_TIME || kindof == RND_SRC_IRQ)
{
uint8_t curr_time = ts.tv_sec * 8 + ts.tv_nsec / (NSEC_PER_SEC / 8);
/* Allow interrupts/timers increase entropy counter at max rate
* of 8 Hz.
*/
if (g_rng.rd_prev_time == curr_time)
{
new_inc = false;
}
else
{
g_rng.rd_prev_time = curr_time;
}
}
if (n > 0)
{
tbuf[0] ^= buf[0];
buf++;
n--;
}
addentropy(tbuf, 1, new_inc);
if (n > 0)
{
addentropy(buf, n, new_inc);
}
}
/****************************************************************************
* Name: up_rngreseed
*
* Description:
* Force reseeding random number generator from entropy pool
*
****************************************************************************/
void up_rngreseed(void)
{
int ret;
ret = nxsem_wait_uninterruptible(&g_rng.rd_sem);
if (ret >= 0)
{
if (g_rng.rd_newentr >= MIN_SEED_NEW_ENTROPY_WORDS)
{
rng_reseed();
}
nxsem_post(&g_rng.rd_sem);
}
}
/****************************************************************************
* Name: up_randompool_initialize
*
* Description:
* Initialize entropy pool and random number generator
*
****************************************************************************/
void up_randompool_initialize(void)
{
rng_init();
#ifdef CONFIG_BOARD_INITRNGSEED
board_init_rngseed();
#endif
}
/****************************************************************************
* Name: arc4random_buf
*
* Description:
* Fill a buffer of arbitrary length with randomness. This is the
* preferred interface for getting random numbers. The traditional
* /dev/random approach is susceptible for things like the attacker
* exhausting file descriptors on purpose.
*
* Note that this function cannot fail, other than by asserting.
*
* Input Parameters:
* bytes - Buffer for returned random bytes
* nbytes - Number of bytes requested.
*
* Returned Value:
* None
*
****************************************************************************/
void arc4random_buf(FAR void *bytes, size_t nbytes)
{
int ret;
do
{
ret = nxsem_wait_uninterruptible(&g_rng.rd_sem);
/* The only possible error should be if we were awakened by
* thread cancellation. At this point, we must continue to acquire
* the semaphore anyway.
*/
DEBUGASSERT(ret == OK || ret == -ECANCELED);
}
while (ret < 0);
rng_buf_internal(bytes, nbytes);
nxsem_post(&g_rng.rd_sem);
}
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