// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) /* * Copyright (C) 2017-2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. * Copyright Matt Mackall <mpm@selenic.com>, 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. Prior to initialization, 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.
*/
/********************************************************************* * * 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 is protected by base_crng->lock, and only increases * its value (from empty->early->ready).
*/ staticenum {
CRNG_EMPTY = 0, /* Little to no entropy collected */
CRNG_EARLY = 1, /* At least POOL_EARLY_BITS collected */
CRNG_READY = 2 /* Fully initialized with POOL_READY_BITS collected */
} crng_init __read_mostly = CRNG_EMPTY; static DEFINE_STATIC_KEY_FALSE(crng_is_ready); #define crng_ready() (static_branch_likely(&crng_is_ready) || crng_init >= CRNG_READY) /* Various types of waiters for crng_init->CRNG_READY transition. */ static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); staticstruct fasync_struct *fasync; static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);
/* Control how we warn userspace. */ staticstruct ratelimit_state urandom_warning =
RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE); staticint ratelimit_disable __read_mostly =
IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
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_{u8, * u16,u32,u64,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. */ staticvoid 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_{u8,u16,u32,u64, * 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 crng is initialised, * or immediately if it already has been. Only use this is you are absolutely * sure it is required. Most users should instead be able to test * `rng_is_initialized()` on demand, or make use of `get_random_bytes_wait()`.
*/ int __cold execute_with_initialized_rng(struct notifier_block *nb)
{ unsignedlong flags; int ret = 0;
spin_lock_irqsave(&random_ready_notifier.lock, flags); if (crng_ready())
nb->notifier_call(nb, 0, NULL); else
ret = raw_notifier_chain_register((struct raw_notifier_head *)&random_ready_notifier.head, nb);
spin_unlock_irqrestore(&random_ready_notifier.lock, flags); return ret;
}
#define warn_unseeded_randomness() \ if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \
printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \
__func__, (void *)_RET_IP_, 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 <https://blog.cr.yp.to/20170723-random.html>. * * There are a few exported interfaces for use by other drivers: * * void get_random_bytes(void *buf, size_t len) * u8 get_random_u8() * u16 get_random_u16() * u32 get_random_u32() * u32 get_random_u32_below(u32 ceil) * u32 get_random_u32_above(u32 floor) * u32 get_random_u32_inclusive(u32 floor, u32 ceil) * u64 get_random_u64() * 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 u8, u16, u32, u64, 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. *
*********************************************************************/
/* * Return the interval until the next reseeding, which is normally * CRNG_RESEED_INTERVAL, but during early boot, it is at an interval * proportional to the uptime.
*/ staticunsignedint crng_reseed_interval(void)
{ staticbool early_boot = true;
/* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */ staticvoid extract_entropy(void *buf, size_t len);
/* This extracts a new crng key from the input pool. */ staticvoid crng_reseed(struct work_struct *work)
{ static DECLARE_DELAYED_WORK(next_reseed, crng_reseed); unsignedlong flags; unsignedlong next_gen;
u8 key[CHACHA_KEY_SIZE];
/* Immediately schedule the next reseeding, so that it fires sooner rather than later. */ if (likely(system_unbound_wq))
queue_delayed_work(system_unbound_wq, &next_reseed, crng_reseed_interval());
extract_entropy(key, sizeof(key));
/* * 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); #ifdef CONFIG_VDSO_GETRANDOM /* base_crng.generation's invalid value is ULONG_MAX, while * vdso_k_rng_data->generation's invalid value is 0, so add one to the * former to arrive at the latter. Use smp_store_release so that this * is ordered with the write above to base_crng.generation. Pairs with * the smp_rmb() before the syscall in the vDSO code. * * Cast to unsigned long for 32-bit architectures, since atomic 64-bit * operations are not supported on those architectures. This is safe * because base_crng.generation is a 32-bit value. On big-endian * architectures it will be stored in the upper 32 bits, but that's okay * because the vDSO side only checks whether the value changed, without * actually using or interpreting the value.
*/
smp_store_release((unsignedlong *)&vdso_k_rng_data->generation, next_gen + 1); #endif if (!static_branch_likely(&crng_is_ready))
crng_init = CRNG_READY;
spin_unlock_irqrestore(&base_crng.lock, flags);
memzero_explicit(key, sizeof(key));
}
/* * This generates a ChaCha block using the provided key, and then * immediately overwrites 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. * * The returned ChaCha state contains within it a copy of the old * key value, at index 4, so the state should always be zeroed out * immediately after using in order to maintain forward secrecy. * If the state cannot be erased in a timely manner, then it is * safer to set the random_data parameter to &chacha_state->x[4] * so that this function overwrites it before returning.
*/ staticvoid crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], struct chacha_state *chacha_state,
u8 *random_data, size_t random_data_len)
{
u8 first_block[CHACHA_BLOCK_SIZE];
/* * 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.
*/ staticvoid crng_make_state(struct chacha_state *chacha_state,
u8 *random_data, size_t random_data_len)
{ unsignedlong 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, extracting * when crng_init is CRNG_EMPTY.
*/ if (!crng_ready()) { bool ready;
spin_lock_irqsave(&base_crng.lock, flags);
ready = crng_ready(); if (!ready) { if (crng_init == CRNG_EMPTY)
extract_entropy(base_crng.key, sizeof(base_crng.key));
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 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);
}
while (len) { if (len < CHACHA_BLOCK_SIZE) {
chacha20_block(&chacha_state, tmp);
memcpy(buf, tmp, len);
memzero_explicit(tmp, sizeof(tmp)); break;
}
chacha20_block(&chacha_state, buf); if (unlikely(chacha_state.x[12] == 0))
++chacha_state.x[13];
len -= CHACHA_BLOCK_SIZE;
buf += CHACHA_BLOCK_SIZE;
}
chacha_zeroize_state(&chacha_state);
}
/* * This returns random bytes in arbitrary quantities. The quality of the * random bytes 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.
*/ void get_random_bytes(void *buf, size_t len)
{
warn_unseeded_randomness();
_get_random_bytes(buf, len);
}
EXPORT_SYMBOL(get_random_bytes);
/* * Immediately overwrite the ChaCha key at index 4 with random * bytes, in case userspace causes copy_to_iter() below to sleep * forever, so that we still retain forward secrecy in that case.
*/
crng_make_state(&chacha_state, (u8 *)&chacha_state.x[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 (iov_iter_count(iter) <= CHACHA_KEY_SIZE) {
ret = copy_to_iter(&chacha_state.x[4], CHACHA_KEY_SIZE, iter); goto out_zero_chacha;
}
for (;;) {
chacha20_block(&chacha_state, block); if (unlikely(chacha_state.x[12] == 0))
++chacha_state.x[13];
copied = copy_to_iter(block, sizeof(block), iter);
ret += copied; if (!iov_iter_count(iter) || copied != sizeof(block)) break;
BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0); if (ret % PAGE_SIZE == 0) { if (signal_pending(current)) break;
cond_resched();
}
}
memzero_explicit(block, sizeof(block));
out_zero_chacha:
chacha_zeroize_state(&chacha_state); return ret ? ret : -EFAULT;
}
/* * 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.
*/
#define DEFINE_BATCHED_ENTROPY(type) \ struct batch_ ##type { \ /* \ * 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. \
*/
type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))]; \
local_lock_t lock; \ unsignedlong generation; \ unsignedint position; \
}; \
\ static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = { \
.lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock), \
.position = UINT_MAX \
}; \
\
type get_random_ ##type(void) \
{ \
type ret; \ unsignedlong flags; \ struct batch_ ##type *batch; \ unsignedlong next_gen; \
\
warn_unseeded_randomness(); \
\ if (!crng_ready()) { \
_get_random_bytes(&ret, sizeof(ret)); \ return ret; \
} \
\
local_lock_irqsave(&batched_entropy_ ##type.lock, flags); \
batch = raw_cpu_ptr(&batched_entropy_##type); \
\
next_gen = READ_ONCE(base_crng.generation); \ if (batch->position >= ARRAY_SIZE(batch->entropy) || \
next_gen != batch->generation) { \
_get_random_bytes(batch->entropy, sizeof(batch->entropy)); \
batch->position = 0; \
batch->generation = next_gen; \
} \
\
ret = batch->entropy[batch->position]; \
batch->entropy[batch->position] = 0; \
++batch->position; \
local_unlock_irqrestore(&batched_entropy_ ##type.lock, flags); \ return ret; \
} \
EXPORT_SYMBOL(get_random_ ##type);
u32 __get_random_u32_below(u32 ceil)
{ /* * This is the slow path for variable ceil. It is still fast, most of * the time, by doing traditional reciprocal multiplication and * opportunistically comparing the lower half to ceil itself, before * falling back to computing a larger bound, and then rejecting samples * whose lower half would indicate a range indivisible by ceil. The use * of `-ceil % ceil` is analogous to `2^32 % ceil`, but is computable * in 32-bits.
*/
u32 rand = get_random_u32();
u64 mult;
/* * This function is technically undefined for ceil == 0, and in fact * for the non-underscored constant version in the header, we build bug * on that. But for the non-constant case, it's convenient to have that * evaluate to being a straight call to get_random_u32(), so that * get_random_u32_inclusive() can work over its whole range without * undefined behavior.
*/ if (unlikely(!ceil)) return rand;
mult = (u64)ceil * rand; if (unlikely((u32)mult < ceil)) {
u32 bound = -ceil % ceil; while (unlikely((u32)mult < bound))
mult = (u64)ceil * get_random_u32();
} return mult >> 32;
}
EXPORT_SYMBOL(__get_random_u32_below);
#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 __cold random_prepare_cpu(unsignedint 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_u8, cpu)->position = UINT_MAX;
per_cpu_ptr(&batched_entropy_u16, cpu)->position = UINT_MAX;
per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX;
per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX; return 0;
} #endif
/********************************************************************** * * Entropy accumulation and extraction routines. * * Callers may add entropy via: * * static void mix_pool_bytes(const void *buf, size_t len) * * After which, if added entropy should be credited: * * static void credit_init_bits(size_t bits) * * Finally, extract entropy via: * * static void extract_entropy(void *buf, size_t len) *
**********************************************************************/
/* * This function adds bytes into the input pool. It does not * update the initialization bit counter; the caller should call * credit_init_bits if this is appropriate.
*/ staticvoid mix_pool_bytes(constvoid *buf, size_t len)
{ unsignedlong flags;
/* * This is an HKDF-like construction for using the hashed collected entropy * as a PRF key, that's then expanded block-by-block.
*/ staticvoid extract_entropy(void *buf, size_t len)
{ unsignedlong flags;
u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; struct { unsignedlong rdseed[32 / sizeof(long)];
size_t counter;
} block;
size_t i, longs;
for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i); if (longs) {
i += longs; continue;
}
longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i); if (longs) {
i += longs; continue;
}
block.rdseed[i++] = random_get_entropy();
}
#define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)
staticvoid __cold _credit_init_bits(size_t bits)
{ static DECLARE_WORK(set_ready, crng_set_ready); unsignedintnew, orig, add; unsignedlong flags; int m;
if (!bits) return;
add = min_t(size_t, bits, POOL_BITS);
orig = READ_ONCE(input_pool.init_bits); do { new = min_t(unsignedint, POOL_BITS, orig + add);
} while (!try_cmpxchg(&input_pool.init_bits, &orig, new));
if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
crng_reseed(NULL); /* Sets crng_init to CRNG_READY under base_crng.lock. */ if (static_key_initialized && system_unbound_wq)
queue_work(system_unbound_wq, &set_ready);
atomic_notifier_call_chain(&random_ready_notifier, 0, NULL); #ifdef CONFIG_VDSO_GETRANDOM
WRITE_ONCE(vdso_k_rng_data->is_ready, true); #endif
wake_up_interruptible(&crng_init_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
pr_notice("crng init done\n");
m = ratelimit_state_get_miss(&urandom_warning); if (m)
pr_notice("%d urandom warning(s) missed due to ratelimiting\n", m);
} elseif (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
spin_lock_irqsave(&base_crng.lock, flags); /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */ if (crng_init == CRNG_EMPTY) {
extract_entropy(base_crng.key, sizeof(base_crng.key));
crng_init = CRNG_EARLY;
}
spin_unlock_irqrestore(&base_crng.lock, flags);
}
}
/********************************************************************** * * 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 len); * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after); * void add_bootloader_randomness(const void *buf, size_t len); * void add_vmfork_randomness(const void *unique_vm_id, size_t len); * void add_interrupt_randomness(int irq); * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value); * void add_disk_randomness(struct gendisk *disk); * * 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_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 called by bootloader drivers, such as EFI * and device tree, and credits its input depending on whether or not the * command line option 'random.trust_bootloader'. * * 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. * * 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 last 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. *
**********************************************************************/
/* * Encode a representation of how long the system has been suspended, * in a way that is distinct from prior system suspends.
*/
ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };
/* * This is called extremely early, before time keeping functionality is * available, but arch randomness is. Interrupts are not yet enabled.
*/ void __init random_init_early(constchar *command_line)
{ unsignedlong entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
size_t i, longs, arch_bits;
/* Reseed if already seeded by earlier phases. */ if (crng_ready())
crng_reseed(NULL); elseif (trust_cpu)
_credit_init_bits(arch_bits);
}
/* * This is called a little bit after the prior function, and now there is * access to timestamps counters. Interrupts are not yet enabled.
*/ void __init random_init(void)
{ unsignedlong entropy = random_get_entropy();
ktime_t now = ktime_get_real();
/* * If we were initialized by the cpu or bootloader before jump labels * or workqueues are initialized, then we should enable the static * branch here, where it's guaranteed that these have been initialized.
*/ if (!static_branch_likely(&crng_is_ready) && crng_init >= CRNG_READY)
crng_set_ready(NULL);
/* Reseed if already seeded by earlier phases. */ if (crng_ready())
crng_reseed(NULL);
WARN_ON(register_pm_notifier(&pm_notifier));
WARN(!entropy, "Missing cycle counter and fallback timer; RNG " "entropy collection will consequently suffer.");
}
/* * 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(constvoid *buf, size_t len)
{ unsignedlong entropy = random_get_entropy(); unsignedlong flags;
/* * Interface for in-kernel drivers of true hardware RNGs. Those devices * may produce endless random bits, so this function will sleep for * some amount of time after, if the sleep_after parameter is true.
*/ void add_hwgenerator_randomness(constvoid *buf, size_t len, size_t entropy, bool sleep_after)
{
mix_pool_bytes(buf, len);
credit_init_bits(entropy);
/* * Throttle writing to once every reseed interval, unless we're not yet * initialized or no entropy is credited.
*/ if (sleep_after && !kthread_should_stop() && (crng_ready() || !entropy))
schedule_timeout_interruptible(crng_reseed_interval());
}
EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
/* * Handle random seed passed by bootloader, and credit it depending * on the command line option 'random.trust_bootloader'.
*/ void __init add_bootloader_randomness(constvoid *buf, size_t len)
{
mix_pool_bytes(buf, len); if (trust_bootloader)
credit_init_bits(len * 8);
}
/* * 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 __cold add_vmfork_randomness(constvoid *unique_vm_id, size_t len)
{
add_device_randomness(unique_vm_id, len); if (crng_ready()) {
crng_reseed(NULL);
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
/* * 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 * four-word SipHash state, while v represents a two-word input.
*/ staticvoid fast_mix(unsignedlong s[4], unsignedlong v1, unsignedlong v2)
{
s[3] ^= v1;
FASTMIX_PERM(s[0], s[1], s[2], s[3]);
s[0] ^= v1;
s[3] ^= v2;
FASTMIX_PERM(s[0], s[1], s[2], s[3]);
s[0] ^= v2;
}
#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 __cold random_online_cpu(unsignedint 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
staticvoid mix_interrupt_randomness(struct timer_list *work)
{ struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix); /* * The size of the copied stack pool is explicitly 2 longs so that we * only ever ingest half of the siphash output each time, retaining * the other half as the next "key" that carries over. The entropy is * supposed to be sufficiently dispersed between bits so on average * we don't wind up "losing" some.
*/ unsignedlong pool[2]; unsignedint count;
/* 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));
count = fast_pool->count;
fast_pool->count = 0;
fast_pool->last = jiffies;
local_irq_enable();
/* There is one of these per entropy source */ struct timer_rand_state { unsignedlong 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 * value "num" is also added to the pool; it should somehow describe * the type of event that just happened.
*/ staticvoid add_timer_randomness(struct timer_rand_state *state, unsignedint num)
{ unsignedlong entropy = random_get_entropy(), now = jiffies, flags; long delta, delta2, delta3; unsignedint bits;
/* * If we're in a hard IRQ, add_interrupt_randomness() will be called * sometime after, so mix into the fast pool.
*/ if (in_hardirq()) {
fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num);
} else {
spin_lock_irqsave(&input_pool.lock, flags);
_mix_pool_bytes(&entropy, sizeof(entropy));
_mix_pool_bytes(&num, sizeof(num));
spin_unlock_irqrestore(&input_pool.lock, flags);
}
if (crng_ready()) return;
/* * 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);
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 11 bits.
*/
bits = min(fls(delta >> 1), 11);
/* * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness() * will run after this, which uses a different crediting scheme of 1 bit * per every 64 interrupts. In order to let that function do accounting * close to the one in this function, we credit a full 64/64 bit per bit, * and then subtract one to account for the extra one added.
*/ if (in_hardirq())
this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1; else
_credit_init_bits(bits);
}
#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);
/* * 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
/* * 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.
*/ staticvoid __cold entropy_timer(struct timer_list *timer)
{ struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer); unsignedlong entropy = random_get_entropy();
mix_pool_bytes(&entropy, sizeof(entropy)); if (atomic_inc_return(&state->samples) % state->samples_per_bit == 0)
credit_init_bits(1);
}
/* * If we have an actual cycle counter, see if we can generate enough entropy * with timing noise.
*/ staticvoid __cold try_to_generate_entropy(void)
{ enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 15 };
u8 stack_bytes[sizeof(struct entropy_timer_state) + SMP_CACHE_BYTES - 1]; struct entropy_timer_state *stack = PTR_ALIGN((void *)stack_bytes, SMP_CACHE_BYTES); unsignedint i, num_different = 0; unsignedlong last = random_get_entropy(); int cpu = -1;
for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
stack->entropy = random_get_entropy(); if (stack->entropy != last)
++num_different;
last = stack->entropy;
}
stack->samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1); if (stack->samples_per_bit > MAX_SAMPLES_PER_BIT) return;
atomic_set(&stack->samples, 0);
timer_setup_on_stack(&stack->timer, entropy_timer, 0); while (!crng_ready() && !signal_pending(current)) { /* * Check !timer_pending() and then ensure that any previous callback has finished * executing by checking timer_delete_sync_try(), before queueing the next one.
*/ if (!timer_pending(&stack->timer) && timer_delete_sync_try(&stack->timer) >= 0) { struct cpumask timer_cpus; unsignedint num_cpus;
/* * Preemption must be disabled here, both to read the current CPU number * and to avoid scheduling a timer on a dead CPU.
*/
preempt_disable();
/* Only schedule callbacks on timer CPUs that are online. */
cpumask_and(&timer_cpus, housekeeping_cpumask(HK_TYPE_TIMER), cpu_online_mask);
num_cpus = cpumask_weight(&timer_cpus); /* In very bizarre case of misconfiguration, fallback to all online. */ if (unlikely(num_cpus == 0)) {
timer_cpus = *cpu_online_mask;
num_cpus = cpumask_weight(&timer_cpus);
}
/* Basic CPU round-robin, which avoids the current CPU. */ do {
cpu = cpumask_next(cpu, &timer_cpus); if (cpu >= nr_cpu_ids)
cpu = cpumask_first(&timer_cpus);
} while (cpu == smp_processor_id() && num_cpus > 1);
/* Expiring the timer at `jiffies` means it's the next tick. */
stack->timer.expires = jiffies;
/********************************************************************** * * 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. *
**********************************************************************/
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 (!crng_ready() && !(flags & GRND_INSECURE)) { if (flags & GRND_NONBLOCK) return -EAGAIN;
ret = wait_for_random_bytes(); if (unlikely(ret)) return ret;
}
ret = import_ubuf(ITER_DEST, ubuf, len, &iter); if (unlikely(ret)) return ret; return get_random_bytes_user(&iter);
}
/* * 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();
ret = wait_for_random_bytes(); if (ret != 0) return ret; return get_random_bytes_user(iter);
}
staticlong random_ioctl(struct file *f, unsignedint cmd, unsignedlong arg)
{ int __user *p = (int __user *)arg; int ent_count;
switch (cmd) { case RNDGETENTCNT: /* Inherently racy, no point locking. */ if (put_user(input_pool.init_bits, 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_init_bits(ent_count); return 0; case RNDADDENTROPY: { struct iov_iter iter;
ssize_t ret; int len;
if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ent_count, p++)) return -EFAULT; if (ent_count < 0) return -EINVAL; if (get_user(len, p++)) return -EFAULT;
ret = import_ubuf(ITER_SOURCE, p, len, &iter); if (unlikely(ret)) return ret;
ret = write_pool_user(&iter); if (unlikely(ret < 0)) return ret; /* Since we're crediting, enforce that it was all written into the pool. */ if (unlikely(ret != len)) return -EFAULT;
credit_init_bits(ent_count); return 0;
} case RNDZAPENTCNT: case RNDCLEARPOOL: /* No longer has any effect. */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; return 0; case RNDRESEEDCRNG: if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (!crng_ready()) return -ENODATA;
crng_reseed(NULL); return 0; default: return -EINVAL;
}
}
staticint random_fasync(int fd, struct file *filp, int on)
{ return fasync_helper(fd, filp, on, &fasync);
}
/******************************************************************** * * 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_READY_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. *
********************************************************************/
/* * 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.
*/ staticint proc_do_uuid(conststruct ctl_table *table, int write, void *buf,
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
};
/* * random_init() is called before sysctl_init(), * so we cannot call register_sysctl_init() in random_init()
*/ staticint __init random_sysctls_init(void)
{
register_sysctl_init("kernel/random", random_table); return 0;
}
device_initcall(random_sysctls_init); #endif
Messung V0.5
¤ Dauer der Verarbeitung: 0.21 Sekunden
(vorverarbeitet)
¤
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung und die Messung sind noch experimentell.
