// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) /* * Copyright (C) 2017-2022 Jason A. Donenfeld . All Rights Reserved. * Copyright Matt Mackall , 2003, 2004, 2005 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All rights reserved. * * This driver produces cryptographically secure pseudorandom data. It is divided * into roughly six sections, each with a section header: * * - Initialization and readiness waiting. * - Fast key erasure RNG, the "crng". * - Entropy accumulation and extraction routines. * - Entropy collection routines. * - Userspace reader/writer interfaces. * - Sysctl interface. * * The high level overview is that there is one input pool, into which * various pieces of data are hashed. Some of that data is then "credited" as * having a certain number of bits of entropy. When enough bits of entropy are * available, the hash is finalized and handed as a key to a stream cipher that * expands it indefinitely for various consumers. This key is periodically * refreshed as the various entropy collectors, described below, add data to the * input pool and credit it. There is currently no Fortuna-like scheduler * involved, which can lead to malicious entropy sources causing a premature * reseed, and the entropy estimates are, at best, conservative guesses. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /********************************************************************* * * Initialization and readiness waiting. * * Much of the RNG infrastructure is devoted to various dependencies * being able to wait until the RNG has collected enough entropy and * is ready for safe consumption. * *********************************************************************/ /* * crng_init = 0 --> Uninitialized * 1 --> Initialized * 2 --> Initialized from input_pool * * crng_init is protected by base_crng->lock, and only increases * its value (from 0->1->2). */ static int crng_init = 0; #define crng_ready() (likely(crng_init > 1)) /* Various types of waiters for crng_init->2 transition. */ static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); static struct fasync_struct *fasync; static DEFINE_SPINLOCK(random_ready_chain_lock); static RAW_NOTIFIER_HEAD(random_ready_chain); /* Control how we warn userspace. */ static struct ratelimit_state unseeded_warning = RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3); static struct ratelimit_state urandom_warning = RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3); static int ratelimit_disable __read_mostly; module_param_named(ratelimit_disable, ratelimit_disable, int, 0644); MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression"); /* * Returns whether or not the input pool has been seeded and thus guaranteed * to supply cryptographically secure random numbers. This applies to: the * /dev/urandom device, the get_random_bytes function, and the get_random_{u32, * ,u64,int,long} family of functions. * * Returns: true if the input pool has been seeded. * false if the input pool has not been seeded. */ bool rng_is_initialized(void) { return crng_ready(); } EXPORT_SYMBOL(rng_is_initialized); /* Used by wait_for_random_bytes(), and considered an entropy collector, below. */ static void try_to_generate_entropy(void); /* * Wait for the input pool to be seeded and thus guaranteed to supply * cryptographically secure random numbers. This applies to: the /dev/urandom * device, the get_random_bytes function, and the get_random_{u32,u64,int,long} * family of functions. Using any of these functions without first calling * this function forfeits the guarantee of security. * * Returns: 0 if the input pool has been seeded. * -ERESTARTSYS if the function was interrupted by a signal. */ int wait_for_random_bytes(void) { while (!crng_ready()) { int ret; try_to_generate_entropy(); ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ); if (ret) return ret > 0 ? 0 : ret; } return 0; } EXPORT_SYMBOL(wait_for_random_bytes); /* * Add a callback function that will be invoked when the input * pool is initialised. * * returns: 0 if callback is successfully added * -EALREADY if pool is already initialised (callback not called) */ int register_random_ready_notifier(struct notifier_block *nb) { unsigned long flags; int ret = -EALREADY; if (crng_ready()) return ret; spin_lock_irqsave(&random_ready_chain_lock, flags); if (!crng_ready()) ret = raw_notifier_chain_register(&random_ready_chain, nb); spin_unlock_irqrestore(&random_ready_chain_lock, flags); return ret; } /* * Delete a previously registered readiness callback function. */ int unregister_random_ready_notifier(struct notifier_block *nb) { unsigned long flags; int ret; spin_lock_irqsave(&random_ready_chain_lock, flags); ret = raw_notifier_chain_unregister(&random_ready_chain, nb); spin_unlock_irqrestore(&random_ready_chain_lock, flags); return ret; } static void process_random_ready_list(void) { unsigned long flags; spin_lock_irqsave(&random_ready_chain_lock, flags); raw_notifier_call_chain(&random_ready_chain, 0, NULL); spin_unlock_irqrestore(&random_ready_chain_lock, flags); } #define warn_unseeded_randomness(previous) \ _warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous)) static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous) { #ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM const bool print_once = false; #else static bool print_once __read_mostly; #endif if (print_once || crng_ready() || (previous && (caller == READ_ONCE(*previous)))) return; WRITE_ONCE(*previous, caller); #ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM print_once = true; #endif if (__ratelimit(&unseeded_warning)) printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", func_name, caller, crng_init); } /********************************************************************* * * Fast key erasure RNG, the "crng". * * These functions expand entropy from the entropy extractor into * long streams for external consumption using the "fast key erasure" * RNG described at . * * There are a few exported interfaces for use by other drivers: * * void get_random_bytes(void *buf, size_t nbytes) * u32 get_random_u32() * u64 get_random_u64() * unsigned int get_random_int() * unsigned long get_random_long() * * These interfaces will return the requested number of random bytes * into the given buffer or as a return value. This is equivalent to * a read from /dev/urandom. The u32, u64, int, and long family of * functions may be higher performance for one-off random integers, * because they do a bit of buffering and do not invoke reseeding * until the buffer is emptied. * *********************************************************************/ enum { CRNG_RESEED_INTERVAL = 300 * HZ, CRNG_INIT_CNT_THRESH = 2 * CHACHA_KEY_SIZE }; static struct { u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long)); unsigned long birth; unsigned long generation; spinlock_t lock; } base_crng = { .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock) }; struct crng { u8 key[CHACHA_KEY_SIZE]; unsigned long generation; local_lock_t lock; }; static DEFINE_PER_CPU(struct crng, crngs) = { .generation = ULONG_MAX, .lock = INIT_LOCAL_LOCK(crngs.lock), }; /* Used by crng_reseed() to extract a new seed from the input pool. */ static bool drain_entropy(void *buf, size_t nbytes, bool force); /* * This extracts a new crng key from the input pool, but only if there is a * sufficient amount of entropy available or force is true, in order to * mitigate bruteforcing of newly added bits. */ static void crng_reseed(bool force) { unsigned long flags; unsigned long next_gen; u8 key[CHACHA_KEY_SIZE]; bool finalize_init = false; /* Only reseed if we can, to prevent brute forcing a small amount of new bits. */ if (!drain_entropy(key, sizeof(key), force)) return; /* * We copy the new key into the base_crng, overwriting the old one, * and update the generation counter. We avoid hitting ULONG_MAX, * because the per-cpu crngs are initialized to ULONG_MAX, so this * forces new CPUs that come online to always initialize. */ spin_lock_irqsave(&base_crng.lock, flags); memcpy(base_crng.key, key, sizeof(base_crng.key)); next_gen = base_crng.generation + 1; if (next_gen == ULONG_MAX) ++next_gen; WRITE_ONCE(base_crng.generation, next_gen); WRITE_ONCE(base_crng.birth, jiffies); if (!crng_ready()) { crng_init = 2; finalize_init = true; } spin_unlock_irqrestore(&base_crng.lock, flags); memzero_explicit(key, sizeof(key)); if (finalize_init) { process_random_ready_list(); wake_up_interruptible(&crng_init_wait); kill_fasync(&fasync, SIGIO, POLL_IN); pr_notice("crng init done\n"); if (unseeded_warning.missed) { pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n", unseeded_warning.missed); unseeded_warning.missed = 0; } if (urandom_warning.missed) { pr_notice("%d urandom warning(s) missed due to ratelimiting\n", urandom_warning.missed); urandom_warning.missed = 0; } } } /* * This generates a ChaCha block using the provided key, and then * immediately overwites that key with half the block. It returns * the resultant ChaCha state to the user, along with the second * half of the block containing 32 bytes of random data that may * be used; random_data_len may not be greater than 32. */ static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], u32 chacha_state[CHACHA_STATE_WORDS], u8 *random_data, size_t random_data_len) { u8 first_block[CHACHA_BLOCK_SIZE]; BUG_ON(random_data_len > 32); chacha_init_consts(chacha_state); memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE); memset(&chacha_state[12], 0, sizeof(u32) * 4); chacha20_block(chacha_state, first_block); memcpy(key, first_block, CHACHA_KEY_SIZE); memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len); memzero_explicit(first_block, sizeof(first_block)); } /* * Return whether the crng seed is considered to be sufficiently * old that a reseeding might be attempted. This happens if the last * reseeding was CRNG_RESEED_INTERVAL ago, or during early boot, at * an interval proportional to the uptime. */ static bool crng_has_old_seed(void) { static bool early_boot = true; unsigned long interval = CRNG_RESEED_INTERVAL; if (unlikely(READ_ONCE(early_boot))) { time64_t uptime = ktime_get_seconds(); if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2) WRITE_ONCE(early_boot, false); else interval = max_t(unsigned int, 5 * HZ, (unsigned int)uptime / 2 * HZ); } return time_after(jiffies, READ_ONCE(base_crng.birth) + interval); } /* * This function returns a ChaCha state that you may use for generating * random data. It also returns up to 32 bytes on its own of random data * that may be used; random_data_len may not be greater than 32. */ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], u8 *random_data, size_t random_data_len) { unsigned long flags; struct crng *crng; BUG_ON(random_data_len > 32); /* * For the fast path, we check whether we're ready, unlocked first, and * then re-check once locked later. In the case where we're really not * ready, we do fast key erasure with the base_crng directly, because * this is what crng_pre_init_inject() mutates during early init. */ if (!crng_ready()) { bool ready; spin_lock_irqsave(&base_crng.lock, flags); ready = crng_ready(); if (!ready) crng_fast_key_erasure(base_crng.key, chacha_state, random_data, random_data_len); spin_unlock_irqrestore(&base_crng.lock, flags); if (!ready) return; } /* * If the base_crng is old enough, we try to reseed, which in turn * bumps the generation counter that we check below. */ if (unlikely(crng_has_old_seed())) crng_reseed(false); local_lock_irqsave(&crngs.lock, flags); crng = raw_cpu_ptr(&crngs); /* * If our per-cpu crng is older than the base_crng, then it means * somebody reseeded the base_crng. In that case, we do fast key * erasure on the base_crng, and use its output as the new key * for our per-cpu crng. This brings us up to date with base_crng. */ if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) { spin_lock(&base_crng.lock); crng_fast_key_erasure(base_crng.key, chacha_state, crng->key, sizeof(crng->key)); crng->generation = base_crng.generation; spin_unlock(&base_crng.lock); } /* * Finally, when we've made it this far, our per-cpu crng has an up * to date key, and we can do fast key erasure with it to produce * some random data and a ChaCha state for the caller. All other * branches of this function are "unlikely", so most of the time we * should wind up here immediately. */ crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len); local_unlock_irqrestore(&crngs.lock, flags); } /* * This function is for crng_init == 0 only. It loads entropy directly * into the crng's key, without going through the input pool. It is, * generally speaking, not very safe, but we use this only at early * boot time when it's better to have something there rather than * nothing. * * If account is set, then the crng_init_cnt counter is incremented. * This shouldn't be set by functions like add_device_randomness(), * where we can't trust the buffer passed to it is guaranteed to be * unpredictable (so it might not have any entropy at all). */ static void crng_pre_init_inject(const void *input, size_t len, bool account) { static int crng_init_cnt = 0; struct blake2s_state hash; unsigned long flags; blake2s_init(&hash, sizeof(base_crng.key)); spin_lock_irqsave(&base_crng.lock, flags); if (crng_init != 0) { spin_unlock_irqrestore(&base_crng.lock, flags); return; } blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); blake2s_update(&hash, input, len); blake2s_final(&hash, base_crng.key); if (account) { crng_init_cnt += min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt); if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { ++base_crng.generation; crng_init = 1; } } spin_unlock_irqrestore(&base_crng.lock, flags); if (crng_init == 1) pr_notice("fast init done\n"); } static void _get_random_bytes(void *buf, size_t nbytes) { u32 chacha_state[CHACHA_STATE_WORDS]; u8 tmp[CHACHA_BLOCK_SIZE]; size_t len; if (!nbytes) return; len = min_t(size_t, 32, nbytes); crng_make_state(chacha_state, buf, len); nbytes -= len; buf += len; while (nbytes) { if (nbytes < CHACHA_BLOCK_SIZE) { chacha20_block(chacha_state, tmp); memcpy(buf, tmp, nbytes); memzero_explicit(tmp, sizeof(tmp)); break; } chacha20_block(chacha_state, buf); if (unlikely(chacha_state[12] == 0)) ++chacha_state[13]; nbytes -= CHACHA_BLOCK_SIZE; buf += CHACHA_BLOCK_SIZE; } memzero_explicit(chacha_state, sizeof(chacha_state)); } /* * This function is the exported kernel interface. It returns some * number of good random numbers, suitable for key generation, seeding * TCP sequence numbers, etc. It does not rely on the hardware random * number generator. For random bytes direct from the hardware RNG * (when available), use get_random_bytes_arch(). In order to ensure * that the randomness provided by this function is okay, the function * wait_for_random_bytes() should be called and return 0 at least once * at any point prior. */ void get_random_bytes(void *buf, size_t nbytes) { static void *previous; warn_unseeded_randomness(&previous); _get_random_bytes(buf, nbytes); } EXPORT_SYMBOL(get_random_bytes); static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) { ssize_t ret = 0; size_t len; u32 chacha_state[CHACHA_STATE_WORDS]; u8 output[CHACHA_BLOCK_SIZE]; if (!nbytes) return 0; /* * Immediately overwrite the ChaCha key at index 4 with random * bytes, in case userspace causes copy_to_user() below to sleep * forever, so that we still retain forward secrecy in that case. */ crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE); /* * However, if we're doing a read of len <= 32, we don't need to * use chacha_state after, so we can simply return those bytes to * the user directly. */ if (nbytes <= CHACHA_KEY_SIZE) { ret = copy_to_user(buf, &chacha_state[4], nbytes) ? -EFAULT : nbytes; goto out_zero_chacha; } do { chacha20_block(chacha_state, output); if (unlikely(chacha_state[12] == 0)) ++chacha_state[13]; len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE); if (copy_to_user(buf, output, len)) { ret = -EFAULT; break; } nbytes -= len; buf += len; ret += len; BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0); if (!(ret % PAGE_SIZE) && nbytes) { if (signal_pending(current)) break; cond_resched(); } } while (nbytes); memzero_explicit(output, sizeof(output)); out_zero_chacha: memzero_explicit(chacha_state, sizeof(chacha_state)); return ret; } /* * Batched entropy returns random integers. The quality of the random * number is good as /dev/urandom. In order to ensure that the randomness * provided by this function is okay, the function wait_for_random_bytes() * should be called and return 0 at least once at any point prior. */ struct batched_entropy { union { /* * We make this 1.5x a ChaCha block, so that we get the * remaining 32 bytes from fast key erasure, plus one full * block from the detached ChaCha state. We can increase * the size of this later if needed so long as we keep the * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. */ u64 entropy_u64[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u64))]; u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))]; }; local_lock_t lock; unsigned long generation; unsigned int position; }; static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = { .lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock), .position = UINT_MAX }; u64 get_random_u64(void) { u64 ret; unsigned long flags; struct batched_entropy *batch; static void *previous; unsigned long next_gen; warn_unseeded_randomness(&previous); local_lock_irqsave(&batched_entropy_u64.lock, flags); batch = raw_cpu_ptr(&batched_entropy_u64); next_gen = READ_ONCE(base_crng.generation); if (batch->position >= ARRAY_SIZE(batch->entropy_u64) || next_gen != batch->generation) { _get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64)); batch->position = 0; batch->generation = next_gen; } ret = batch->entropy_u64[batch->position]; batch->entropy_u64[batch->position] = 0; ++batch->position; local_unlock_irqrestore(&batched_entropy_u64.lock, flags); return ret; } EXPORT_SYMBOL(get_random_u64); static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = { .lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock), .position = UINT_MAX }; u32 get_random_u32(void) { u32 ret; unsigned long flags; struct batched_entropy *batch; static void *previous; unsigned long next_gen; warn_unseeded_randomness(&previous); local_lock_irqsave(&batched_entropy_u32.lock, flags); batch = raw_cpu_ptr(&batched_entropy_u32); next_gen = READ_ONCE(base_crng.generation); if (batch->position >= ARRAY_SIZE(batch->entropy_u32) || next_gen != batch->generation) { _get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32)); batch->position = 0; batch->generation = next_gen; } ret = batch->entropy_u32[batch->position]; batch->entropy_u32[batch->position] = 0; ++batch->position; local_unlock_irqrestore(&batched_entropy_u32.lock, flags); return ret; } EXPORT_SYMBOL(get_random_u32); #ifdef CONFIG_SMP /* * This function is called when the CPU is coming up, with entry * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP. */ int random_prepare_cpu(unsigned int cpu) { /* * When the cpu comes back online, immediately invalidate both * the per-cpu crng and all batches, so that we serve fresh * randomness. */ per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX; per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX; per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX; return 0; } #endif /** * randomize_page - Generate a random, page aligned address * @start: The smallest acceptable address the caller will take. * @range: The size of the area, starting at @start, within which the * random address must fall. * * If @start + @range would overflow, @range is capped. * * NOTE: Historical use of randomize_range, which this replaces, presumed that * @start was already page aligned. We now align it regardless. * * Return: A page aligned address within [start, start + range). On error, * @start is returned. */ unsigned long randomize_page(unsigned long start, unsigned long range) { if (!PAGE_ALIGNED(start)) { range -= PAGE_ALIGN(start) - start; start = PAGE_ALIGN(start); } if (start > ULONG_MAX - range) range = ULONG_MAX - start; range >>= PAGE_SHIFT; if (range == 0) return start; return start + (get_random_long() % range << PAGE_SHIFT); } /* * This function will use the architecture-specific hardware random * number generator if it is available. It is not recommended for * use. Use get_random_bytes() instead. It returns the number of * bytes filled in. */ size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes) { size_t left = nbytes; u8 *p = buf; while (left) { unsigned long v; size_t chunk = min_t(size_t, left, sizeof(unsigned long)); if (!arch_get_random_long(&v)) break; memcpy(p, &v, chunk); p += chunk; left -= chunk; } return nbytes - left; } EXPORT_SYMBOL(get_random_bytes_arch); /********************************************************************** * * Entropy accumulation and extraction routines. * * Callers may add entropy via: * * static void mix_pool_bytes(const void *in, size_t nbytes) * * After which, if added entropy should be credited: * * static void credit_entropy_bits(size_t nbits) * * Finally, extract entropy via these two, with the latter one * setting the entropy count to zero and extracting only if there * is POOL_MIN_BITS entropy credited prior or force is true: * * static void extract_entropy(void *buf, size_t nbytes) * static bool drain_entropy(void *buf, size_t nbytes, bool force) * **********************************************************************/ enum { POOL_BITS = BLAKE2S_HASH_SIZE * 8, POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ }; /* For notifying userspace should write into /dev/random. */ static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); static struct { struct blake2s_state hash; spinlock_t lock; unsigned int entropy_count; } input_pool = { .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE), BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4, BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 }, .hash.outlen = BLAKE2S_HASH_SIZE, .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), }; static void _mix_pool_bytes(const void *in, size_t nbytes) { blake2s_update(&input_pool.hash, in, nbytes); } /* * This function adds bytes into the entropy "pool". It does not * update the entropy estimate. The caller should call * credit_entropy_bits if this is appropriate. */ static void mix_pool_bytes(const void *in, size_t nbytes) { unsigned long flags; spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(in, nbytes); spin_unlock_irqrestore(&input_pool.lock, flags); } static void credit_entropy_bits(size_t nbits) { unsigned int entropy_count, orig, add; if (!nbits) return; add = min_t(size_t, nbits, POOL_BITS); do { orig = READ_ONCE(input_pool.entropy_count); entropy_count = min_t(unsigned int, POOL_BITS, orig + add); } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); if (!crng_ready() && entropy_count >= POOL_MIN_BITS) crng_reseed(false); } /* * This is an HKDF-like construction for using the hashed collected entropy * as a PRF key, that's then expanded block-by-block. */ static void extract_entropy(void *buf, size_t nbytes) { unsigned long flags; u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; struct { unsigned long rdseed[32 / sizeof(long)]; size_t counter; } block; size_t i; for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) { if (!arch_get_random_seed_long(&block.rdseed[i]) && !arch_get_random_long(&block.rdseed[i])) block.rdseed[i] = random_get_entropy(); } spin_lock_irqsave(&input_pool.lock, flags); /* seed = HASHPRF(last_key, entropy_input) */ blake2s_final(&input_pool.hash, seed); /* next_key = HASHPRF(seed, RDSEED || 0) */ block.counter = 0; blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed)); blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key)); spin_unlock_irqrestore(&input_pool.lock, flags); memzero_explicit(next_key, sizeof(next_key)); while (nbytes) { i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE); /* output = HASHPRF(seed, RDSEED || ++counter) */ ++block.counter; blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed)); nbytes -= i; buf += i; } memzero_explicit(seed, sizeof(seed)); memzero_explicit(&block, sizeof(block)); } /* * First we make sure we have POOL_MIN_BITS of entropy in the pool unless force * is true, and then we set the entropy count to zero (but don't actually touch * any data). Only then can we extract a new key with extract_entropy(). */ static bool drain_entropy(void *buf, size_t nbytes, bool force) { unsigned int entropy_count; do { entropy_count = READ_ONCE(input_pool.entropy_count); if (!force && entropy_count < POOL_MIN_BITS) return false; } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); extract_entropy(buf, nbytes); wake_up_interruptible(&random_write_wait); kill_fasync(&fasync, SIGIO, POLL_OUT); return true; } /********************************************************************** * * Entropy collection routines. * * The following exported functions are used for pushing entropy into * the above entropy accumulation routines: * * void add_device_randomness(const void *buf, size_t size); * void add_input_randomness(unsigned int type, unsigned int code, * unsigned int value); * void add_disk_randomness(struct gendisk *disk); * void add_hwgenerator_randomness(const void *buffer, size_t count, * size_t entropy); * void add_bootloader_randomness(const void *buf, size_t size); * void add_vmfork_randomness(const void *unique_vm_id, size_t size); * void add_interrupt_randomness(int irq); * * add_device_randomness() adds data to the input pool that * is likely to differ between two devices (or possibly even per boot). * This would be things like MAC addresses or serial numbers, or the * read-out of the RTC. This does *not* credit any actual entropy to * the pool, but it initializes the pool to different values for devices * that might otherwise be identical and have very little entropy * available to them (particularly common in the embedded world). * * add_input_randomness() uses the input layer interrupt timing, as well * as the event type information from the hardware. * * add_disk_randomness() uses what amounts to the seek time of block * layer request events, on a per-disk_devt basis, as input to the * entropy pool. Note that high-speed solid state drives with very low * seek times do not make for good sources of entropy, as their seek * times are usually fairly consistent. * * The above two routines try to estimate how many bits of entropy * to credit. They do this by keeping track of the first and second * order deltas of the event timings. * * add_hwgenerator_randomness() is for true hardware RNGs, and will credit * entropy as specified by the caller. If the entropy pool is full it will * block until more entropy is needed. * * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or * add_device_randomness(), depending on whether or not the configuration * option CONFIG_RANDOM_TRUST_BOOTLOADER is set. * * add_vmfork_randomness() adds a unique (but not necessarily secret) ID * representing the current instance of a VM to the pool, without crediting, * and then force-reseeds the crng so that it takes effect immediately. * * add_interrupt_randomness() uses the interrupt timing as random * inputs to the entropy pool. Using the cycle counters and the irq source * as inputs, it feeds the input pool roughly once a second or after 64 * interrupts, crediting 1 bit of entropy for whichever comes first. * **********************************************************************/ static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); static bool trust_bootloader __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER); static int __init parse_trust_cpu(char *arg) { return kstrtobool(arg, &trust_cpu); } static int __init parse_trust_bootloader(char *arg) { return kstrtobool(arg, &trust_bootloader); } early_param("random.trust_cpu", parse_trust_cpu); early_param("random.trust_bootloader", parse_trust_bootloader); /* * The first collection of entropy occurs at system boot while interrupts * are still turned off. Here we push in RDSEED, a timestamp, and utsname(). * Depending on the above configuration knob, RDSEED may be considered * sufficient for initialization. Note that much earlier setup may already * have pushed entropy into the input pool by the time we get here. */ int __init rand_initialize(void) { size_t i; ktime_t now = ktime_get_real(); bool arch_init = true; unsigned long rv; #if defined(LATENT_ENTROPY_PLUGIN) static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy; _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed)); #endif for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) { if (!arch_get_random_seed_long_early(&rv) && !arch_get_random_long_early(&rv)) { rv = random_get_entropy(); arch_init = false; } _mix_pool_bytes(&rv, sizeof(rv)); } _mix_pool_bytes(&now, sizeof(now)); _mix_pool_bytes(utsname(), sizeof(*(utsname()))); extract_entropy(base_crng.key, sizeof(base_crng.key)); ++base_crng.generation; if (arch_init && trust_cpu && !crng_ready()) { crng_init = 2; pr_notice("crng init done (trusting CPU's manufacturer)\n"); } if (ratelimit_disable) { urandom_warning.interval = 0; unseeded_warning.interval = 0; } return 0; } /* * Add device- or boot-specific data to the input pool to help * initialize it. * * None of this adds any entropy; it is meant to avoid the problem of * the entropy pool having similar initial state across largely * identical devices. */ void add_device_randomness(const void *buf, size_t size) { cycles_t cycles = random_get_entropy(); unsigned long flags, now = jiffies; if (crng_init == 0 && size) crng_pre_init_inject(buf, size, false); spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(&cycles, sizeof(cycles)); _mix_pool_bytes(&now, sizeof(now)); _mix_pool_bytes(buf, size); spin_unlock_irqrestore(&input_pool.lock, flags); } EXPORT_SYMBOL(add_device_randomness); /* There is one of these per entropy source */ struct timer_rand_state { unsigned long last_time; long last_delta, last_delta2; }; /* * This function adds entropy to the entropy "pool" by using timing * delays. It uses the timer_rand_state structure to make an estimate * of how many bits of entropy this call has added to the pool. * * The number "num" is also added to the pool - it should somehow describe * the type of event which just happened. This is currently 0-255 for * keyboard scan codes, and 256 upwards for interrupts. */ static void add_timer_randomness(struct timer_rand_state *state, unsigned int num) { cycles_t cycles = random_get_entropy(); unsigned long flags, now = jiffies; long delta, delta2, delta3; spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(&cycles, sizeof(cycles)); _mix_pool_bytes(&now, sizeof(now)); _mix_pool_bytes(&num, sizeof(num)); spin_unlock_irqrestore(&input_pool.lock, flags); /* * Calculate number of bits of randomness we probably added. * We take into account the first, second and third-order deltas * in order to make our estimate. */ delta = now - READ_ONCE(state->last_time); WRITE_ONCE(state->last_time, now); delta2 = delta - READ_ONCE(state->last_delta); WRITE_ONCE(state->last_delta, delta); delta3 = delta2 - READ_ONCE(state->last_delta2); WRITE_ONCE(state->last_delta2, delta2); if (delta < 0) delta = -delta; if (delta2 < 0) delta2 = -delta2; if (delta3 < 0) delta3 = -delta3; if (delta > delta2) delta = delta2; if (delta > delta3) delta = delta3; /* * delta is now minimum absolute delta. * Round down by 1 bit on general principles, * and limit entropy estimate to 12 bits. */ credit_entropy_bits(min_t(unsigned int, fls(delta >> 1), 11)); } void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) { static unsigned char last_value; static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES }; /* Ignore autorepeat and the like. */ if (value == last_value) return; last_value = value; add_timer_randomness(&input_timer_state, (type << 4) ^ code ^ (code >> 4) ^ value); } EXPORT_SYMBOL_GPL(add_input_randomness); #ifdef CONFIG_BLOCK void add_disk_randomness(struct gendisk *disk) { if (!disk || !disk->random) return; /* First major is 1, so we get >= 0x200 here. */ add_timer_randomness(disk->random, 0x100 + disk_devt(disk)); } EXPORT_SYMBOL_GPL(add_disk_randomness); void rand_initialize_disk(struct gendisk *disk) { struct timer_rand_state *state; /* * If kzalloc returns null, we just won't use that entropy * source. */ state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL); if (state) { state->last_time = INITIAL_JIFFIES; disk->random = state; } } #endif /* * Interface for in-kernel drivers of true hardware RNGs. * Those devices may produce endless random bits and will be throttled * when our pool is full. */ void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy) { if (unlikely(crng_init == 0 && entropy < POOL_MIN_BITS)) { crng_pre_init_inject(buffer, count, true); mix_pool_bytes(buffer, count); return; } /* * Throttle writing if we're above the trickle threshold. * We'll be woken up again once below POOL_MIN_BITS, when * the calling thread is about to terminate, or once * CRNG_RESEED_INTERVAL has elapsed. */ wait_event_interruptible_timeout(random_write_wait, !system_wq || kthread_should_stop() || input_pool.entropy_count < POOL_MIN_BITS, CRNG_RESEED_INTERVAL); mix_pool_bytes(buffer, count); credit_entropy_bits(entropy); } EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); /* * Handle random seed passed by bootloader. * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise * it would be regarded as device data. * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER. */ void add_bootloader_randomness(const void *buf, size_t size) { if (trust_bootloader) add_hwgenerator_randomness(buf, size, size * 8); else add_device_randomness(buf, size); } EXPORT_SYMBOL_GPL(add_bootloader_randomness); #if IS_ENABLED(CONFIG_VMGENID) static BLOCKING_NOTIFIER_HEAD(vmfork_chain); /* * Handle a new unique VM ID, which is unique, not secret, so we * don't credit it, but we do immediately force a reseed after so * that it's used by the crng posthaste. */ void add_vmfork_randomness(const void *unique_vm_id, size_t size) { add_device_randomness(unique_vm_id, size); if (crng_ready()) { crng_reseed(true); pr_notice("crng reseeded due to virtual machine fork\n"); } blocking_notifier_call_chain(&vmfork_chain, 0, NULL); } #if IS_MODULE(CONFIG_VMGENID) EXPORT_SYMBOL_GPL(add_vmfork_randomness); #endif int register_random_vmfork_notifier(struct notifier_block *nb) { return blocking_notifier_chain_register(&vmfork_chain, nb); } EXPORT_SYMBOL_GPL(register_random_vmfork_notifier); int unregister_random_vmfork_notifier(struct notifier_block *nb) { return blocking_notifier_chain_unregister(&vmfork_chain, nb); } EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier); #endif struct fast_pool { struct work_struct mix; unsigned long pool[4]; unsigned long last; unsigned int count; u16 reg_idx; }; static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = { #ifdef CONFIG_64BIT /* SipHash constants */ .pool = { 0x736f6d6570736575UL, 0x646f72616e646f6dUL, 0x6c7967656e657261UL, 0x7465646279746573UL } #else /* HalfSipHash constants */ .pool = { 0, 0, 0x6c796765U, 0x74656462U } #endif }; /* * This is [Half]SipHash-1-x, starting from an empty key. Because * the key is fixed, it assumes that its inputs are non-malicious, * and therefore this has no security on its own. s represents the * 128 or 256-bit SipHash state, while v represents a 128-bit input. */ static void fast_mix(unsigned long s[4], const unsigned long *v) { size_t i; for (i = 0; i < 16 / sizeof(long); ++i) { s[3] ^= v[i]; #ifdef CONFIG_64BIT s[0] += s[1]; s[1] = rol64(s[1], 13); s[1] ^= s[0]; s[0] = rol64(s[0], 32); s[2] += s[3]; s[3] = rol64(s[3], 16); s[3] ^= s[2]; s[0] += s[3]; s[3] = rol64(s[3], 21); s[3] ^= s[0]; s[2] += s[1]; s[1] = rol64(s[1], 17); s[1] ^= s[2]; s[2] = rol64(s[2], 32); #else s[0] += s[1]; s[1] = rol32(s[1], 5); s[1] ^= s[0]; s[0] = rol32(s[0], 16); s[2] += s[3]; s[3] = rol32(s[3], 8); s[3] ^= s[2]; s[0] += s[3]; s[3] = rol32(s[3], 7); s[3] ^= s[0]; s[2] += s[1]; s[1] = rol32(s[1], 13); s[1] ^= s[2]; s[2] = rol32(s[2], 16); #endif s[0] ^= v[i]; } } #ifdef CONFIG_SMP /* * This function is called when the CPU has just come online, with * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE. */ int random_online_cpu(unsigned int cpu) { /* * During CPU shutdown and before CPU onlining, add_interrupt_ * randomness() may schedule mix_interrupt_randomness(), and * set the MIX_INFLIGHT flag. However, because the worker can * be scheduled on a different CPU during this period, that * flag will never be cleared. For that reason, we zero out * the flag here, which runs just after workqueues are onlined * for the CPU again. This also has the effect of setting the * irq randomness count to zero so that new accumulated irqs * are fresh. */ per_cpu_ptr(&irq_randomness, cpu)->count = 0; return 0; } #endif static unsigned long get_reg(struct fast_pool *f, struct pt_regs *regs) { unsigned long *ptr = (unsigned long *)regs; unsigned int idx; if (regs == NULL) return 0; idx = READ_ONCE(f->reg_idx); if (idx >= sizeof(struct pt_regs) / sizeof(unsigned long)) idx = 0; ptr += idx++; WRITE_ONCE(f->reg_idx, idx); return *ptr; } static void mix_interrupt_randomness(struct work_struct *work) { struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix); /* * The size of the copied stack pool is explicitly 16 bytes so that we * tax mix_pool_byte()'s compression function the same amount on all * platforms. This means on 64-bit we copy half the pool into this, * while on 32-bit we copy all of it. The entropy is supposed to be * sufficiently dispersed between bits that in the sponge-like * half case, on average we don't wind up "losing" some. */ u8 pool[16]; /* Check to see if we're running on the wrong CPU due to hotplug. */ local_irq_disable(); if (fast_pool != this_cpu_ptr(&irq_randomness)) { local_irq_enable(); return; } /* * Copy the pool to the stack so that the mixer always has a * consistent view, before we reenable irqs again. */ memcpy(pool, fast_pool->pool, sizeof(pool)); fast_pool->count = 0; fast_pool->last = jiffies; local_irq_enable(); if (unlikely(crng_init == 0)) { crng_pre_init_inject(pool, sizeof(pool), true); mix_pool_bytes(pool, sizeof(pool)); } else { mix_pool_bytes(pool, sizeof(pool)); credit_entropy_bits(1); } memzero_explicit(pool, sizeof(pool)); } void add_interrupt_randomness(int irq) { enum { MIX_INFLIGHT = 1U << 31 }; cycles_t cycles = random_get_entropy(); unsigned long now = jiffies; struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness); struct pt_regs *regs = get_irq_regs(); unsigned int new_count; union { u32 u32[4]; u64 u64[2]; unsigned long longs[16 / sizeof(long)]; } irq_data; if (cycles == 0) cycles = get_reg(fast_pool, regs); if (sizeof(cycles) == 8) irq_data.u64[0] = cycles ^ rol64(now, 32) ^ irq; else { irq_data.u32[0] = cycles ^ irq; irq_data.u32[1] = now; } if (sizeof(unsigned long) == 8) irq_data.u64[1] = regs ? instruction_pointer(regs) : _RET_IP_; else { irq_data.u32[2] = regs ? instruction_pointer(regs) : _RET_IP_; irq_data.u32[3] = get_reg(fast_pool, regs); } fast_mix(fast_pool->pool, irq_data.longs); new_count = ++fast_pool->count; if (new_count & MIX_INFLIGHT) return; if (new_count < 64 && (!time_after(now, fast_pool->last + HZ) || unlikely(crng_init == 0))) return; if (unlikely(!fast_pool->mix.func)) INIT_WORK(&fast_pool->mix, mix_interrupt_randomness); fast_pool->count |= MIX_INFLIGHT; queue_work_on(raw_smp_processor_id(), system_highpri_wq, &fast_pool->mix); } EXPORT_SYMBOL_GPL(add_interrupt_randomness); /* * Each time the timer fires, we expect that we got an unpredictable * jump in the cycle counter. Even if the timer is running on another * CPU, the timer activity will be touching the stack of the CPU that is * generating entropy.. * * Note that we don't re-arm the timer in the timer itself - we are * happy to be scheduled away, since that just makes the load more * complex, but we do not want the timer to keep ticking unless the * entropy loop is running. * * So the re-arming always happens in the entropy loop itself. */ static void entropy_timer(struct timer_list *t) { credit_entropy_bits(1); } /* * If we have an actual cycle counter, see if we can * generate enough entropy with timing noise */ static void try_to_generate_entropy(void) { struct { cycles_t cycles; struct timer_list timer; } stack; stack.cycles = random_get_entropy(); /* Slow counter - or none. Don't even bother */ if (stack.cycles == random_get_entropy()) return; timer_setup_on_stack(&stack.timer, entropy_timer, 0); while (!crng_ready() && !signal_pending(current)) { if (!timer_pending(&stack.timer)) mod_timer(&stack.timer, jiffies + 1); mix_pool_bytes(&stack.cycles, sizeof(stack.cycles)); schedule(); stack.cycles = random_get_entropy(); } del_timer_sync(&stack.timer); destroy_timer_on_stack(&stack.timer); mix_pool_bytes(&stack.cycles, sizeof(stack.cycles)); } /********************************************************************** * * Userspace reader/writer interfaces. * * getrandom(2) is the primary modern interface into the RNG and should * be used in preference to anything else. * * Reading from /dev/random has the same functionality as calling * getrandom(2) with flags=0. In earlier versions, however, it had * vastly different semantics and should therefore be avoided, to * prevent backwards compatibility issues. * * Reading from /dev/urandom has the same functionality as calling * getrandom(2) with flags=GRND_INSECURE. Because it does not block * waiting for the RNG to be ready, it should not be used. * * Writing to either /dev/random or /dev/urandom adds entropy to * the input pool but does not credit it. * * Polling on /dev/random indicates when the RNG is initialized, on * the read side, and when it wants new entropy, on the write side. * * Both /dev/random and /dev/urandom have the same set of ioctls for * adding entropy, getting the entropy count, zeroing the count, and * reseeding the crng. * **********************************************************************/ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, flags) { if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)) return -EINVAL; /* * Requesting insecure and blocking randomness at the same time makes * no sense. */ if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM)) return -EINVAL; if (count > INT_MAX) count = INT_MAX; if (!(flags & GRND_INSECURE) && !crng_ready()) { int ret; if (flags & GRND_NONBLOCK) return -EAGAIN; ret = wait_for_random_bytes(); if (unlikely(ret)) return ret; } return get_random_bytes_user(buf, count); } static __poll_t random_poll(struct file *file, poll_table *wait) { __poll_t mask; poll_wait(file, &crng_init_wait, wait); poll_wait(file, &random_write_wait, wait); mask = 0; if (crng_ready()) mask |= EPOLLIN | EPOLLRDNORM; if (input_pool.entropy_count < POOL_MIN_BITS) mask |= EPOLLOUT | EPOLLWRNORM; return mask; } static int write_pool(const char __user *ubuf, size_t count) { size_t len; int ret = 0; u8 block[BLAKE2S_BLOCK_SIZE]; while (count) { len = min(count, sizeof(block)); if (copy_from_user(block, ubuf, len)) { ret = -EFAULT; goto out; } count -= len; ubuf += len; mix_pool_bytes(block, len); cond_resched(); } out: memzero_explicit(block, sizeof(block)); return ret; } static ssize_t random_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos) { int ret; ret = write_pool(buffer, count); if (ret) return ret; return (ssize_t)count; } static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { static int maxwarn = 10; /* * Opportunistically attempt to initialize the RNG on platforms that * have fast cycle counters, but don't (for now) require it to succeed. */ if (!crng_ready()) try_to_generate_entropy(); if (!crng_ready() && maxwarn > 0) { maxwarn--; if (__ratelimit(&urandom_warning)) pr_notice("%s: uninitialized urandom read (%zd bytes read)\n", current->comm, nbytes); } return get_random_bytes_user(buf, nbytes); } static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { int ret; ret = wait_for_random_bytes(); if (ret != 0) return ret; return get_random_bytes_user(buf, nbytes); } static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) { int size, ent_count; int __user *p = (int __user *)arg; int retval; switch (cmd) { case RNDGETENTCNT: /* Inherently racy, no point locking. */ if (put_user(input_pool.entropy_count, p)) return -EFAULT; return 0; case RNDADDTOENTCNT: if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ent_count, p)) return -EFAULT; if (ent_count < 0) return -EINVAL; credit_entropy_bits(ent_count); return 0; case RNDADDENTROPY: if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ent_count, p++)) return -EFAULT; if (ent_count < 0) return -EINVAL; if (get_user(size, p++)) return -EFAULT; retval = write_pool((const char __user *)p, size); if (retval < 0) return retval; credit_entropy_bits(ent_count); return 0; case RNDZAPENTCNT: case RNDCLEARPOOL: /* * Clear the entropy pool counters. We no longer clear * the entropy pool, as that's silly. */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (xchg(&input_pool.entropy_count, 0) >= POOL_MIN_BITS) { wake_up_interruptible(&random_write_wait); kill_fasync(&fasync, SIGIO, POLL_OUT); } return 0; case RNDRESEEDCRNG: if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (!crng_ready()) return -ENODATA; crng_reseed(false); return 0; default: return -EINVAL; } } static int random_fasync(int fd, struct file *filp, int on) { return fasync_helper(fd, filp, on, &fasync); } const struct file_operations random_fops = { .read = random_read, .write = random_write, .poll = random_poll, .unlocked_ioctl = random_ioctl, .compat_ioctl = compat_ptr_ioctl, .fasync = random_fasync, .llseek = noop_llseek, }; const struct file_operations urandom_fops = { .read = urandom_read, .write = random_write, .unlocked_ioctl = random_ioctl, .compat_ioctl = compat_ptr_ioctl, .fasync = random_fasync, .llseek = noop_llseek, }; /******************************************************************** * * Sysctl interface. * * These are partly unused legacy knobs with dummy values to not break * userspace and partly still useful things. They are usually accessible * in /proc/sys/kernel/random/ and are as follows: * * - boot_id - a UUID representing the current boot. * * - uuid - a random UUID, different each time the file is read. * * - poolsize - the number of bits of entropy that the input pool can * hold, tied to the POOL_BITS constant. * * - entropy_avail - the number of bits of entropy currently in the * input pool. Always <= poolsize. * * - write_wakeup_threshold - the amount of entropy in the input pool * below which write polls to /dev/random will unblock, requesting * more entropy, tied to the POOL_MIN_BITS constant. It is writable * to avoid breaking old userspaces, but writing to it does not * change any behavior of the RNG. * * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL. * It is writable to avoid breaking old userspaces, but writing * to it does not change any behavior of the RNG. * ********************************************************************/ #ifdef CONFIG_SYSCTL #include static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ; static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS; static int sysctl_poolsize = POOL_BITS; static u8 sysctl_bootid[UUID_SIZE]; /* * This function is used to return both the bootid UUID, and random * UUID. The difference is in whether table->data is NULL; if it is, * then a new UUID is generated and returned to the user. */ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { u8 tmp_uuid[UUID_SIZE], *uuid; char uuid_string[UUID_STRING_LEN + 1]; struct ctl_table fake_table = { .data = uuid_string, .maxlen = UUID_STRING_LEN }; if (write) return -EPERM; uuid = table->data; if (!uuid) { uuid = tmp_uuid; generate_random_uuid(uuid); } else { static DEFINE_SPINLOCK(bootid_spinlock); spin_lock(&bootid_spinlock); if (!uuid[8]) generate_random_uuid(uuid); spin_unlock(&bootid_spinlock); } snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid); return proc_dostring(&fake_table, 0, buffer, lenp, ppos); } /* The same as proc_dointvec, but writes don't change anything. */ static int proc_do_rointvec(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { return write ? 0 : proc_dointvec(table, 0, buffer, lenp, ppos); } static struct ctl_table random_table[] = { { .procname = "poolsize", .data = &sysctl_poolsize, .maxlen = sizeof(int), .mode = 0444, .proc_handler = proc_dointvec, }, { .procname = "entropy_avail", .data = &input_pool.entropy_count, .maxlen = sizeof(int), .mode = 0444, .proc_handler = proc_dointvec, }, { .procname = "write_wakeup_threshold", .data = &sysctl_random_write_wakeup_bits, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_do_rointvec, }, { .procname = "urandom_min_reseed_secs", .data = &sysctl_random_min_urandom_seed, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_do_rointvec, }, { .procname = "boot_id", .data = &sysctl_bootid, .mode = 0444, .proc_handler = proc_do_uuid, }, { .procname = "uuid", .mode = 0444, .proc_handler = proc_do_uuid, }, { } }; /* * rand_initialize() is called before sysctl_init(), * so we cannot call register_sysctl_init() in rand_initialize() */ static int __init random_sysctls_init(void) { register_sysctl_init("kernel/random", random_table); return 0; } device_initcall(random_sysctls_init); #endif