/**************************************************************************** * 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 #include #include #include #include #include #include #include #include #include #include #include /**************************************************************************** * 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 */ 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_gettime(CLOCK_REALTIME, &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); }