blob: 964f4828f50751a086be66e057ae4036c74cd0b8 [file] [log] [blame]
// 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/genhd.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/siphash.h>
#include <linux/uio.h>
#include <crypto/chacha20.h>
#include <crypto/blake2s.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;
#define crng_ready() (likely(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 DEFINE_SPINLOCK(random_ready_chain_lock);
static RAW_NOTIFIER_HEAD(random_ready_chain);
/* 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_{u32,
* ,u64,int,long} family of functions.
*
* Returns: true if the input pool has been seeded.
* false if the input pool has not been seeded.
*/
bool rng_is_initialized(void)
{
return crng_ready();
}
EXPORT_SYMBOL(rng_is_initialized);
/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
static void try_to_generate_entropy(void);
/*
* Wait for the input pool to be seeded and thus guaranteed to supply
* cryptographically secure random numbers. This applies to: the /dev/urandom
* device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
* family of functions. Using any of these functions without first calling
* this function forfeits the guarantee of security.
*
* Returns: 0 if the input pool has been seeded.
* -ERESTARTSYS if the function was interrupted by a signal.
*/
int wait_for_random_bytes(void)
{
while (!crng_ready()) {
int ret;
try_to_generate_entropy();
ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
if (ret)
return ret > 0 ? 0 : ret;
}
return 0;
}
EXPORT_SYMBOL(wait_for_random_bytes);
/*
* Add a callback function that will be invoked when the input
* pool is initialised.
*
* returns: 0 if callback is successfully added
* -EALREADY if pool is already initialised (callback not called)
*/
int __cold register_random_ready_notifier(struct notifier_block *nb)
{
unsigned long flags;
int ret = -EALREADY;
if (crng_ready())
return ret;
spin_lock_irqsave(&random_ready_chain_lock, flags);
if (!crng_ready())
ret = raw_notifier_chain_register(&random_ready_chain, nb);
spin_unlock_irqrestore(&random_ready_chain_lock, flags);
return ret;
}
/*
* Delete a previously registered readiness callback function.
*/
int __cold unregister_random_ready_notifier(struct notifier_block *nb)
{
unsigned long flags;
int ret;
spin_lock_irqsave(&random_ready_chain_lock, flags);
ret = raw_notifier_chain_unregister(&random_ready_chain, nb);
spin_unlock_irqrestore(&random_ready_chain_lock, flags);
return ret;
}
static void __cold process_random_ready_list(void)
{
unsigned long flags;
spin_lock_irqsave(&random_ready_chain_lock, flags);
raw_notifier_call_chain(&random_ready_chain, 0, NULL);
spin_unlock_irqrestore(&random_ready_chain_lock, flags);
}
#define warn_unseeded_randomness() \
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)
* u32 get_random_u32()
* u64 get_random_u64()
* unsigned int get_random_int()
* unsigned long get_random_long()
*
* These interfaces will return the requested number of random bytes
* into the given buffer or as a return value. This is equivalent to
* a read from /dev/urandom. The u32, u64, int, and long family of
* functions may be higher performance for one-off random integers,
* because they do a bit of buffering and do not invoke reseeding
* until the buffer is emptied.
*
*********************************************************************/
enum {
CRNG_RESEED_START_INTERVAL = HZ,
CRNG_RESEED_INTERVAL = 60 * HZ
};
static struct {
u8 key[CHACHA20_KEY_SIZE] __aligned(__alignof__(long));
unsigned long birth;
unsigned long generation;
spinlock_t lock;
} base_crng = {
.lock = __SPIN_LOCK_UNLOCKED(base_crng.lock)
};
struct crng {
u8 key[CHACHA20_KEY_SIZE];
unsigned long generation;
};
static DEFINE_PER_CPU(struct crng, crngs) = {
.generation = ULONG_MAX
};
/* 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(void)
{
unsigned long flags;
unsigned long next_gen;
u8 key[CHACHA20_KEY_SIZE];
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);
WRITE_ONCE(base_crng.birth, jiffies);
if (!crng_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 overwites that key with half the block. It returns
* the resultant ChaCha state to the user, along with the second
* half of the block containing 32 bytes of random data that may
* be used; random_data_len may not be greater than 32.
*
* 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[CHACHA20_KEY_SIZE],
u32 chacha_state[CHACHA20_BLOCK_SIZE / sizeof(u32)],
u8 *random_data, size_t random_data_len)
{
u8 first_block[CHACHA20_BLOCK_SIZE];
BUG_ON(random_data_len > 32);
chacha_init_consts(chacha_state);
memcpy(&chacha_state[4], key, CHACHA20_KEY_SIZE);
memset(&chacha_state[12], 0, sizeof(u32) * 4);
chacha20_block(chacha_state, first_block);
memcpy(key, first_block, CHACHA20_KEY_SIZE);
memcpy(random_data, first_block + CHACHA20_KEY_SIZE, random_data_len);
memzero_explicit(first_block, sizeof(first_block));
}
/*
* Return whether the crng seed is considered to be sufficiently old
* that a reseeding is needed. This happens if the last reseeding
* was CRNG_RESEED_INTERVAL ago, or during early boot, at an interval
* proportional to the uptime.
*/
static bool crng_has_old_seed(void)
{
static bool early_boot = true;
unsigned long interval = CRNG_RESEED_INTERVAL;
if (unlikely(READ_ONCE(early_boot))) {
time64_t uptime = ktime_get_seconds();
if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2)
WRITE_ONCE(early_boot, false);
else
interval = max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
(unsigned int)uptime / 2 * HZ);
}
return time_is_before_jiffies(READ_ONCE(base_crng.birth) + interval);
}
/*
* This function returns a ChaCha state that you may use for generating
* random data. It also returns up to 32 bytes on its own of random data
* that may be used; random_data_len may not be greater than 32.
*/
static void crng_make_state(u32 chacha_state[CHACHA20_BLOCK_SIZE / sizeof(u32)],
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;
}
/*
* If the base_crng is old enough, we reseed, which in turn bumps the
* generation counter that we check below.
*/
if (unlikely(crng_has_old_seed()))
crng_reseed();
local_irq_save(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_irq_restore(flags);
}
static void _get_random_bytes(void *buf, size_t len)
{
u32 chacha_state[CHACHA20_BLOCK_SIZE / sizeof(u32)];
u8 tmp[CHACHA20_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 < CHACHA20_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 -= CHACHA20_BLOCK_SIZE;
buf += CHACHA20_BLOCK_SIZE;
}
memzero_explicit(chacha_state, sizeof(chacha_state));
}
/*
* This function is the exported kernel interface. It returns some
* number of good random numbers, suitable for key generation, seeding
* TCP sequence numbers, etc. It does not rely on the hardware random
* number generator. For random bytes direct from the hardware RNG
* (when available), use get_random_bytes_arch(). In order to ensure
* that the randomness provided by this function is okay, the function
* wait_for_random_bytes() should be called and return 0 at least once
* at any point prior.
*/
void get_random_bytes(void *buf, size_t 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[CHACHA20_BLOCK_SIZE / sizeof(u32)];
u8 block[CHACHA20_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_user() below to sleep
* forever, so that we still retain forward secrecy in that case.
*/
crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA20_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) <= CHACHA20_KEY_SIZE) {
ret = copy_to_iter(&chacha_state[4], CHACHA20_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) * CHACHA20_BLOCK_SIZE. \
*/ \
type entropy[CHACHA20_BLOCK_SIZE * 3 / (2 * sizeof(type))]; \
unsigned long generation; \
unsigned int position; \
}; \
\
static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = { \
.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_irq_save(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_irq_restore(flags); \
return ret; \
} \
EXPORT_SYMBOL(get_random_ ##type);
DEFINE_BATCHED_ENTROPY(u64)
DEFINE_BATCHED_ENTROPY(u32)
#ifdef CONFIG_SMP
/*
* This function is called when the CPU is coming up, with entry
* CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP.
*/
int __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_u32, cpu)->position = UINT_MAX;
per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX;
return 0;
}
#endif
/*
* This function will use the architecture-specific hardware random
* number generator if it is available. It is not recommended for
* use. Use get_random_bytes() instead. It returns the number of
* bytes filled in.
*/
size_t __must_check get_random_bytes_arch(void *buf, size_t len)
{
size_t left = len;
u8 *p = buf;
while (left) {
unsigned long v;
size_t block_len = min_t(size_t, left, sizeof(unsigned long));
if (!arch_get_random_long(&v))
break;
memcpy(p, &v, block_len);
p += block_len;
left -= block_len;
}
return len - left;
}
EXPORT_SYMBOL(get_random_bytes_arch);
/**********************************************************************
*
* 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;
for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
if (!arch_get_random_seed_long(&block.rdseed[i]) &&
!arch_get_random_long(&block.rdseed[i]))
block.rdseed[i] = random_get_entropy();
}
spin_lock_irqsave(&input_pool.lock, flags);
/* seed = HASHPRF(last_key, entropy_input) */
blake2s_final(&input_pool.hash, seed);
/* next_key = HASHPRF(seed, RDSEED || 0) */
block.counter = 0;
blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
spin_unlock_irqrestore(&input_pool.lock, flags);
memzero_explicit(next_key, sizeof(next_key));
while (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)
{
unsigned int new, orig, add;
unsigned long flags;
if (!bits)
return;
add = min_t(size_t, bits, POOL_BITS);
do {
orig = READ_ONCE(input_pool.init_bits);
new = min_t(unsigned int, POOL_BITS, orig + add);
} while (cmpxchg(&input_pool.init_bits, orig, new) != orig);
if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
process_random_ready_list();
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);
* void add_bootloader_randomness(const void *buf, 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
* configuration option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
*
* 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 = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
static bool trust_bootloader __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
static int __init parse_trust_cpu(char *arg)
{
return kstrtobool(arg, &trust_cpu);
}
static int __init parse_trust_bootloader(char *arg)
{
return kstrtobool(arg, &trust_bootloader);
}
early_param("random.trust_cpu", parse_trust_cpu);
early_param("random.trust_bootloader", parse_trust_bootloader);
/*
* The first collection of entropy occurs at system boot while interrupts
* are still turned off. Here we push in latent entropy, RDSEED, a timestamp,
* utsname(), and the command line. Depending on the above configuration knob,
* RDSEED may be considered sufficient for initialization. Note that much
* earlier setup may already have pushed entropy into the input pool by the
* time we get here.
*/
int __init random_init(const char *command_line)
{
ktime_t now = ktime_get_real();
unsigned int i, arch_bits;
unsigned long entropy;
#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 = BLAKE2S_BLOCK_SIZE * 8;
i < BLAKE2S_BLOCK_SIZE; i += sizeof(entropy)) {
if (!arch_get_random_seed_long_early(&entropy) &&
!arch_get_random_long_early(&entropy)) {
entropy = random_get_entropy();
arch_bits -= sizeof(entropy) * 8;
}
_mix_pool_bytes(&entropy, sizeof(entropy));
}
_mix_pool_bytes(&now, sizeof(now));
_mix_pool_bytes(utsname(), sizeof(*(utsname())));
_mix_pool_bytes(command_line, strlen(command_line));
add_latent_entropy();
if (crng_ready())
crng_reseed();
else if (trust_cpu)
_credit_init_bits(arch_bits);
return 0;
}
/*
* Add device- or boot-specific data to the input pool to help
* initialize it.
*
* None of this adds any entropy; it is meant to avoid the problem of
* the entropy pool having similar initial state across largely
* identical devices.
*/
void add_device_randomness(const void *buf, size_t 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 and will be throttled
* when our pool is full.
*/
void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy)
{
mix_pool_bytes(buf, len);
credit_init_bits(entropy);
/*
* Throttle writing to once every CRNG_RESEED_INTERVAL, unless
* we're not yet initialized.
*/
if (!kthread_should_stop() && crng_ready())
schedule_timeout_interruptible(CRNG_RESEED_INTERVAL);
}
EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
/*
* Handle random seed passed by bootloader, and credit it if
* CONFIG_RANDOM_TRUST_BOOTLOADER is set.
*/
void __init add_bootloader_randomness(const void *buf, size_t len)
{
mix_pool_bytes(buf, len);
if (trust_bootloader)
credit_init_bits(len * 8);
}
struct fast_pool {
unsigned long pool[4];
unsigned long last;
unsigned int count;
struct timer_list mix;
};
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
};
/*
* 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(unsigned long data)
{
struct fast_pool *fast_pool = (struct fast_pool *)data;
/*
* 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;
if (unlikely(!fast_pool->mix.data))
setup_timer(&fast_pool->mix, mix_interrupt_randomness, (unsigned long)fast_pool);
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_irq()) {
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_irq())
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
/*
* 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(unsigned long data)
{
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)
{
struct {
unsigned long entropy;
struct timer_list timer;
} stack;
stack.entropy = random_get_entropy();
/* Slow counter - or none. Don't even bother */
if (stack.entropy == random_get_entropy())
return;
__setup_timer_on_stack(&stack.timer, entropy_timer, 0, 0);
while (!crng_ready() && !signal_pending(current)) {
if (!timer_pending(&stack.timer))
mod_timer(&stack.timer, jiffies + 1);
mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
schedule();
stack.entropy = random_get_entropy();
}
del_timer_sync(&stack.timer);
destroy_timer_on_stack(&stack.timer);
mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
}
/**********************************************************************
*
* 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(READ, ubuf, len, &iov, &iter);
if (unlikely(ret))
return ret;
return get_random_bytes_user(&iter);
}
static unsigned int random_poll(struct file *file, poll_table *wait)
{
poll_wait(file, &crng_init_wait, wait);
return crng_ready() ? POLLIN | POLLRDNORM : POLLOUT | POLLWRNORM;
}
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;
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) ||
(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(WRITE, 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();
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,
.fasync = random_fasync,
.llseek = noop_llseek,
.splice_read = generic_file_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,
.fasync = random_fasync,
.llseek = noop_llseek,
.splice_read = generic_file_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 __user *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 __user *buf,
size_t *lenp, loff_t *ppos)
{
return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos);
}
extern struct ctl_table random_table[];
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,
},
{ }
};
#endif /* CONFIG_SYSCTL */