Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1699 insertions, 0 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
new file mode 100644
index 0000000000..3cb37760df
--- /dev/null
+++ b/drivers/char/random.c
@@ -0,0 +1,1699 @@
+// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
+/*
+ * Copyright (C) 2017-2022 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.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/utsname.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/major.h>
+#include <linux/string.h>
+#include <linux/fcntl.h>
+#include <linux/slab.h>
+#include <linux/random.h>
+#include <linux/poll.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/blkdev.h>
+#include <linux/interrupt.h>
+#include <linux/mm.h>
+#include <linux/nodemask.h>
+#include <linux/spinlock.h>
+#include <linux/kthread.h>
+#include <linux/percpu.h>
+#include <linux/ptrace.h>
+#include <linux/workqueue.h>
+#include <linux/irq.h>
+#include <linux/ratelimit.h>
+#include <linux/syscalls.h>
+#include <linux/completion.h>
+#include <linux/uuid.h>
+#include <linux/uaccess.h>
+#include <linux/suspend.h>
+#include <linux/siphash.h>
+#include <linux/sched/isolation.h>
+#include <crypto/chacha.h>
+#include <crypto/blake2s.h>
+#include <asm/archrandom.h>
+#include <asm/processor.h>
+#include <asm/irq.h>
+#include <asm/irq_regs.h>
+#include <asm/io.h>
+
+/*********************************************************************
+ *
+ * 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).
+ */
+static enum {
+	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);
+static struct fasync_struct *fasync;
+static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);
+
+/* Control how we warn userspace. */
+static struct ratelimit_state urandom_warning =
+	RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
+static int 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);
+
+static void __cold crng_set_ready(struct work_struct *work)
+{
+	static_branch_enable(&crng_is_ready);
+}
+
+/* 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_{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)
+{
+	unsigned long 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.
+ *
+ *********************************************************************/
+
+enum {
+	CRNG_RESEED_START_INTERVAL = HZ,
+	CRNG_RESEED_INTERVAL = 60 * HZ
+};
+
+static struct {
+	u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long));
+	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),
+};
+
+/*
+ * 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.
+ */
+static unsigned int crng_reseed_interval(void)
+{
+	static bool early_boot = true;
+
+	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
+			return max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
+				     (unsigned int)uptime / 2 * HZ);
+	}
+	return CRNG_RESEED_INTERVAL;
+}
+
+/* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */
+static void extract_entropy(void *buf, size_t len);
+
+/* This extracts a new crng key from the input pool. */
+static void crng_reseed(struct work_struct *work)
+{
+	static DECLARE_DELAYED_WORK(next_reseed, crng_reseed);
+	unsigned long flags;
+	unsigned long 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);
+	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[4] so
+ * that this function overwrites it before returning.
+ */
+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));
+}
+
+/*
+ * 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, 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;
+	}
+
+	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);
+}
+
+static void _get_random_bytes(void *buf, size_t len)
+{
+	u32 chacha_state[CHACHA_STATE_WORDS];
+	u8 tmp[CHACHA_BLOCK_SIZE];
+	size_t first_block_len;
+
+	if (!len)
+		return;
+
+	first_block_len = min_t(size_t, 32, len);
+	crng_make_state(chacha_state, buf, first_block_len);
+	len -= first_block_len;
+	buf += first_block_len;
+
+	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[12] == 0))
+			++chacha_state[13];
+		len -= CHACHA_BLOCK_SIZE;
+		buf += CHACHA_BLOCK_SIZE;
+	}
+
+	memzero_explicit(chacha_state, sizeof(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);
+
+static ssize_t get_random_bytes_user(struct iov_iter *iter)
+{
+	u32 chacha_state[CHACHA_STATE_WORDS];
+	u8 block[CHACHA_BLOCK_SIZE];
+	size_t ret = 0, copied;
+
+	if (unlikely(!iov_iter_count(iter)))
+		return 0;
+
+	/*
+	 * 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[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[4], CHACHA_KEY_SIZE, iter);
+		goto out_zero_chacha;
+	}
+
+	for (;;) {
+		chacha20_block(chacha_state, block);
+		if (unlikely(chacha_state[12] == 0))
+			++chacha_state[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:
+	memzero_explicit(chacha_state, sizeof(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;							\
+	unsigned long generation;						\
+	unsigned int 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;								\
+	unsigned long flags;							\
+	struct batch_ ##type *batch;						\
+	unsigned long 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);
+
+DEFINE_BATCHED_ENTROPY(u8)
+DEFINE_BATCHED_ENTROPY(u16)
+DEFINE_BATCHED_ENTROPY(u32)
+DEFINE_BATCHED_ENTROPY(u64)
+
+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(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_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)
+ *
+ **********************************************************************/
+
+enum {
+	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
+	POOL_READY_BITS = POOL_BITS, /* When crng_init->CRNG_READY */
+	POOL_EARLY_BITS = POOL_READY_BITS / 2 /* When crng_init->CRNG_EARLY */
+};
+
+static struct {
+	struct blake2s_state hash;
+	spinlock_t lock;
+	unsigned int init_bits;
+} 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 *buf, size_t len)
+{
+	blake2s_update(&input_pool.hash, buf, 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.
+ */
+static void mix_pool_bytes(const void *buf, size_t len)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&input_pool.lock, flags);
+	_mix_pool_bytes(buf, len);
+	spin_unlock_irqrestore(&input_pool.lock, flags);
+}
+
+/*
+ * 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 len)
+{
+	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, 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();
+	}
+
+	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 (len) {
+		i = min_t(size_t, len, BLAKE2S_HASH_SIZE);
+		/* output = HASHPRF(seed, RDSEED || ++counter) */
+		++block.counter;
+		blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
+		len -= i;
+		buf += i;
+	}
+
+	memzero_explicit(seed, sizeof(seed));
+	memzero_explicit(&block, sizeof(block));
+}
+
+#define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)
+
+static void __cold _credit_init_bits(size_t bits)
+{
+	static struct execute_work set_ready;
+	unsigned int new, orig, add;
+	unsigned long flags;
+
+	if (!bits)
+		return;
+
+	add = min_t(size_t, bits, POOL_BITS);
+
+	orig = READ_ONCE(input_pool.init_bits);
+	do {
+		new = min_t(unsigned int, 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)
+			execute_in_process_context(crng_set_ready, &set_ready);
+		atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
+		wake_up_interruptible(&crng_init_wait);
+		kill_fasync(&fasync, SIGIO, POLL_IN);
+		pr_notice("crng init done\n");
+		if (urandom_warning.missed)
+			pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
+				  urandom_warning.missed);
+	} else if (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.
+ *
+ **********************************************************************/
+
+static bool trust_cpu __initdata = true;
+static bool trust_bootloader __initdata = true;
+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);
+
+static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
+{
+	unsigned long flags, entropy = random_get_entropy();
+
+	/*
+	 * 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() };
+
+	spin_lock_irqsave(&input_pool.lock, flags);
+	_mix_pool_bytes(&action, sizeof(action));
+	_mix_pool_bytes(stamps, sizeof(stamps));
+	_mix_pool_bytes(&entropy, sizeof(entropy));
+	spin_unlock_irqrestore(&input_pool.lock, flags);
+
+	if (crng_ready() && (action == PM_RESTORE_PREPARE ||
+	    (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) &&
+	     !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) {
+		crng_reseed(NULL);
+		pr_notice("crng reseeded on system resumption\n");
+	}
+	return 0;
+}
+
+static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification };
+
+/*
+ * 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(const char *command_line)
+{
+	unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
+	size_t i, longs, arch_bits;
+
+#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, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
+		longs = arch_get_random_seed_longs(entropy, ARRAY_SIZE(entropy) - i);
+		if (longs) {
+			_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
+			i += longs;
+			continue;
+		}
+		longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i);
+		if (longs) {
+			_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
+			i += longs;
+			continue;
+		}
+		arch_bits -= sizeof(*entropy) * 8;
+		++i;
+	}
+
+	_mix_pool_bytes(init_utsname(), sizeof(*(init_utsname())));
+	_mix_pool_bytes(command_line, strlen(command_line));
+
+	/* Reseed if already seeded by earlier phases. */
+	if (crng_ready())
+		crng_reseed(NULL);
+	else if (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)
+{
+	unsigned long entropy = random_get_entropy();
+	ktime_t now = ktime_get_real();
+
+	_mix_pool_bytes(&now, sizeof(now));
+	_mix_pool_bytes(&entropy, sizeof(entropy));
+	add_latent_entropy();
+
+	/*
+	 * If we were initialized by the cpu or bootloader before jump labels
+	 * are initialized, then we should enable the static branch here, where
+	 * it's guaranteed that jump labels 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(const void *buf, size_t len)
+{
+	unsigned long entropy = random_get_entropy();
+	unsigned long flags;
+
+	spin_lock_irqsave(&input_pool.lock, flags);
+	_mix_pool_bytes(&entropy, sizeof(entropy));
+	_mix_pool_bytes(buf, len);
+	spin_unlock_irqrestore(&input_pool.lock, flags);
+}
+EXPORT_SYMBOL(add_device_randomness);
+
+/*
+ * 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(const void *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(const void *buf, size_t len)
+{
+	mix_pool_bytes(buf, len);
+	if (trust_bootloader)
+		credit_init_bits(len * 8);
+}
+
+#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 __cold add_vmfork_randomness(const void *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
+
+int __cold register_random_vmfork_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&vmfork_chain, nb);
+}
+EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
+
+int __cold 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 {
+	unsigned long pool[4];
+	unsigned long last;
+	unsigned int count;
+	struct timer_list mix;
+};
+
+static void mix_interrupt_randomness(struct timer_list *work);
+
+static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
+#ifdef CONFIG_64BIT
+#define FASTMIX_PERM SIPHASH_PERMUTATION
+	.pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 },
+#else
+#define FASTMIX_PERM HSIPHASH_PERMUTATION
+	.pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 },
+#endif
+	.mix = __TIMER_INITIALIZER(mix_interrupt_randomness, 0)
+};
+
+/*
+ * 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.
+ */
+static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long 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(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 void 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.
+	 */
+	unsigned long pool[2];
+	unsigned int 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();
+
+	mix_pool_bytes(pool, sizeof(pool));
+	credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8));
+
+	memzero_explicit(pool, sizeof(pool));
+}
+
+void add_interrupt_randomness(int irq)
+{
+	enum { MIX_INFLIGHT = 1U << 31 };
+	unsigned long entropy = random_get_entropy();
+	struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
+	struct pt_regs *regs = get_irq_regs();
+	unsigned int new_count;
+
+	fast_mix(fast_pool->pool, entropy,
+		 (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq));
+	new_count = ++fast_pool->count;
+
+	if (new_count & MIX_INFLIGHT)
+		return;
+
+	if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ))
+		return;
+
+	fast_pool->count |= MIX_INFLIGHT;
+	if (!timer_pending(&fast_pool->mix)) {
+		fast_pool->mix.expires = jiffies;
+		add_timer_on(&fast_pool->mix, raw_smp_processor_id());
+	}
+}
+EXPORT_SYMBOL_GPL(add_interrupt_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
+ * value "num" is also added to the pool; it should somehow describe
+ * the type of event that just happened.
+ */
+static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
+{
+	unsigned long entropy = random_get_entropy(), now = jiffies, flags;
+	long delta, delta2, delta3;
+	unsigned int 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);
+
+	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 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);
+}
+
+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 __cold 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
+
+struct entropy_timer_state {
+	unsigned long entropy;
+	struct timer_list timer;
+	atomic_t samples;
+	unsigned int samples_per_bit;
+};
+
+/*
+ * 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 __cold entropy_timer(struct timer_list *timer)
+{
+	struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
+	unsigned long 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.
+ */
+static void __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);
+	unsigned int i, num_different = 0;
+	unsigned long 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 try_to_del_timer_sync(), before queueing the next one.
+		 */
+		if (!timer_pending(&stack->timer) && try_to_del_timer_sync(&stack->timer) >= 0) {
+			struct cpumask timer_cpus;
+			unsigned int 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;
+
+			add_timer_on(&stack->timer, cpu);
+
+			preempt_enable();
+		}
+		mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));
+		schedule();
+		stack->entropy = random_get_entropy();
+	}
+	mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));
+
+	del_timer_sync(&stack->timer);
+	destroy_timer_on_stack(&stack->timer);
+}
+
+
+/**********************************************************************
+ *
+ * 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 *, ubuf, size_t, len, unsigned int, flags)
+{
+	struct iov_iter iter;
+	struct iovec iov;
+	int ret;
+
+	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_single_range(ITER_DEST, ubuf, len, &iov, &iter);
+	if (unlikely(ret))
+		return ret;
+	return get_random_bytes_user(&iter);
+}
+
+static __poll_t random_poll(struct file *file, poll_table *wait)
+{
+	poll_wait(file, &crng_init_wait, wait);
+	return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
+}
+
+static ssize_t write_pool_user(struct iov_iter *iter)
+{
+	u8 block[BLAKE2S_BLOCK_SIZE];
+	ssize_t ret = 0;
+	size_t copied;
+
+	if (unlikely(!iov_iter_count(iter)))
+		return 0;
+
+	for (;;) {
+		copied = copy_from_iter(block, sizeof(block), iter);
+		ret += copied;
+		mix_pool_bytes(block, 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));
+	return ret ? ret : -EFAULT;
+}
+
+static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
+{
+	return write_pool_user(iter);
+}
+
+static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
+{
+	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()) {
+		if (!ratelimit_disable && maxwarn <= 0)
+			++urandom_warning.missed;
+		else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
+			--maxwarn;
+			pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
+				  current->comm, iov_iter_count(iter));
+		}
+	}
+
+	return get_random_bytes_user(iter);
+}
+
+static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
+{
+	int ret;
+
+	if (!crng_ready() &&
+	    ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
+	     (kiocb->ki_filp->f_flags & O_NONBLOCK)))
+		return -EAGAIN;
+
+	ret = wait_for_random_bytes();
+	if (ret != 0)
+		return ret;
+	return get_random_bytes_user(iter);
+}
+
+static long random_ioctl(struct file *f, unsigned int cmd, unsigned long 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;
+		struct iovec iov;
+		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_single_range(ITER_SOURCE, p, len, &iov, &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;
+	}
+}
+
+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_iter = random_read_iter,
+	.write_iter = random_write_iter,
+	.poll = random_poll,
+	.unlocked_ioctl = random_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+	.fasync = random_fasync,
+	.llseek = noop_llseek,
+	.splice_read = copy_splice_read,
+	.splice_write = iter_file_splice_write,
+};
+
+const struct file_operations urandom_fops = {
+	.read_iter = urandom_read_iter,
+	.write_iter = random_write_iter,
+	.unlocked_ioctl = random_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+	.fasync = random_fasync,
+	.llseek = noop_llseek,
+	.splice_read = copy_splice_read,
+	.splice_write = iter_file_splice_write,
+};
+
+
+/********************************************************************
+ *
+ * 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.
+ *
+ ********************************************************************/
+
+#ifdef CONFIG_SYSCTL
+
+#include <linux/sysctl.h>
+
+static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
+static int sysctl_random_write_wakeup_bits = POOL_READY_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 *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
+	};
+
+	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, buf, 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 *buf,
+			    size_t *lenp, loff_t *ppos)
+{
+	return write ? 0 : proc_dointvec(table, 0, buf, 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.init_bits,
+		.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,
+	},
+	{ }
+};
+
+/*
+ * random_init() is called before sysctl_init(),
+ * so we cannot call register_sysctl_init() in random_init()
+ */
+static int __init random_sysctls_init(void)
+{
+	register_sysctl_init("kernel/random", random_table);
+	return 0;
+}
+device_initcall(random_sysctls_init);
+#endif