diff options
| -rw-r--r-- | drivers/char/random.c | 186 |
1 files changed, 68 insertions, 118 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index a2a032ceb108..9e971fb9e16b 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -15,14 +15,12 @@ * - Sysctl interface. * * The high level overview is that there is one input pool, into which - * various pieces of data are hashed. Some of that data is then "credited" as - * having a certain number of bits of entropy. When enough bits of entropy are - * available, the hash is finalized and handed as a key to a stream cipher that - * expands it indefinitely for various consumers. This key is periodically - * refreshed as the various entropy collectors, described below, add data to the - * input pool and credit it. There is currently no Fortuna-like scheduler - * involved, which can lead to malicious entropy sources causing a premature - * reseed, and the entropy estimates are, at best, conservative guesses. + * 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 @@ -232,7 +230,10 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller, void * *********************************************************************/ -enum { CRNG_RESEED_INTERVAL = 300 * HZ }; +enum { + CRNG_RESEED_START_INTERVAL = HZ, + CRNG_RESEED_INTERVAL = 60 * HZ +}; static struct { u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long)); @@ -254,26 +255,18 @@ static DEFINE_PER_CPU(struct crng, crngs) = { .lock = INIT_LOCAL_LOCK(crngs.lock), }; -/* Used by crng_reseed() to extract a new seed from the input pool. */ -static bool drain_entropy(void *buf, size_t nbytes, bool force); -/* Used by crng_make_state() to extract a new seed when crng_init==0. */ +/* 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 nbytes); -/* - * This extracts a new crng key from the input pool, but only if there is a - * sufficient amount of entropy available or force is true, in order to - * mitigate bruteforcing of newly added bits. - */ -static void crng_reseed(bool force) +/* This extracts a new crng key from the input pool. */ +static void crng_reseed(void) { unsigned long flags; unsigned long next_gen; u8 key[CHACHA_KEY_SIZE]; bool finalize_init = false; - /* Only reseed if we can, to prevent brute forcing a small amount of new bits. */ - if (!drain_entropy(key, sizeof(key), force)) - return; + extract_entropy(key, sizeof(key)); /* * We copy the new key into the base_crng, overwriting the old one, @@ -345,10 +338,10 @@ static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], } /* - * Return whether the crng seed is considered to be sufficiently - * old that a reseeding might be attempted. This happens if the last - * reseeding was CRNG_RESEED_INTERVAL ago, or during early boot, at - * an interval proportional to the uptime. + * 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) { @@ -360,7 +353,7 @@ static bool crng_has_old_seed(void) if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2) WRITE_ONCE(early_boot, false); else - interval = max_t(unsigned int, 5 * HZ, + interval = max_t(unsigned int, CRNG_RESEED_START_INTERVAL, (unsigned int)uptime / 2 * HZ); } return time_after(jiffies, READ_ONCE(base_crng.birth) + interval); @@ -402,11 +395,11 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], } /* - * If the base_crng is old enough, we try to reseed, which in turn - * bumps the generation counter that we check below. + * 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(false); + crng_reseed(); local_lock_irqsave(&crngs.lock, flags); crng = raw_cpu_ptr(&crngs); @@ -735,30 +728,24 @@ EXPORT_SYMBOL(get_random_bytes_arch); * * After which, if added entropy should be credited: * - * static void credit_entropy_bits(size_t nbits) + * static void credit_init_bits(size_t nbits) * - * Finally, extract entropy via these two, with the latter one - * setting the entropy count to zero and extracting only if there - * is POOL_MIN_BITS entropy credited prior or force is true: + * Finally, extract entropy via: * * static void extract_entropy(void *buf, size_t nbytes) - * static bool drain_entropy(void *buf, size_t nbytes, bool force) * **********************************************************************/ enum { POOL_BITS = BLAKE2S_HASH_SIZE * 8, - POOL_MIN_BITS = POOL_BITS, /* No point in settling for less. */ - POOL_FAST_INIT_BITS = POOL_MIN_BITS / 2 + POOL_INIT_BITS = POOL_BITS, /* No point in settling for less. */ + POOL_FAST_INIT_BITS = POOL_INIT_BITS / 2 }; -/* For notifying userspace should write into /dev/random. */ -static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); - static struct { struct blake2s_state hash; spinlock_t lock; - unsigned int entropy_count; + unsigned int init_bits; } input_pool = { .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE), BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4, @@ -773,9 +760,9 @@ static void _mix_pool_bytes(const void *in, size_t nbytes) } /* - * This function adds bytes into the entropy "pool". It does not - * update the entropy estimate. The caller should call - * credit_entropy_bits if this is appropriate. + * 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 *in, size_t nbytes) { @@ -832,43 +819,24 @@ static void extract_entropy(void *buf, size_t nbytes) memzero_explicit(&block, sizeof(block)); } -/* - * First we make sure we have POOL_MIN_BITS of entropy in the pool unless force - * is true, and then we set the entropy count to zero (but don't actually touch - * any data). Only then can we extract a new key with extract_entropy(). - */ -static bool drain_entropy(void *buf, size_t nbytes, bool force) -{ - unsigned int entropy_count; - do { - entropy_count = READ_ONCE(input_pool.entropy_count); - if (!force && entropy_count < POOL_MIN_BITS) - return false; - } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); - extract_entropy(buf, nbytes); - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - return true; -} - -static void credit_entropy_bits(size_t nbits) +static void credit_init_bits(size_t nbits) { - unsigned int entropy_count, orig, add; + unsigned int init_bits, orig, add; unsigned long flags; - if (!nbits) + if (crng_ready() || !nbits) return; add = min_t(size_t, nbits, POOL_BITS); do { - orig = READ_ONCE(input_pool.entropy_count); - entropy_count = min_t(unsigned int, POOL_BITS, orig + add); - } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); + orig = READ_ONCE(input_pool.init_bits); + init_bits = min_t(unsigned int, POOL_BITS, orig + add); + } while (cmpxchg(&input_pool.init_bits, orig, init_bits) != orig); - if (!crng_ready() && entropy_count >= POOL_MIN_BITS) - crng_reseed(false); - else if (unlikely(crng_init == 0 && entropy_count >= POOL_FAST_INIT_BITS)) { + if (!crng_ready() && init_bits >= POOL_INIT_BITS) + crng_reseed(); + else if (unlikely(crng_init == 0 && init_bits >= POOL_FAST_INIT_BITS)) { spin_lock_irqsave(&base_crng.lock, flags); if (crng_init == 0) { extract_entropy(base_crng.key, sizeof(base_crng.key)); @@ -968,7 +936,7 @@ static int random_pm_notification(struct notifier_block *nb, unsigned long actio if (crng_ready() && (action == PM_RESTORE_PREPARE || (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) && !IS_ENABLED(CONFIG_ANDROID)))) { - crng_reseed(true); + crng_reseed(); pr_notice("crng reseeded on system resumption\n"); } return 0; @@ -1006,13 +974,10 @@ int __init rand_initialize(void) _mix_pool_bytes(&now, sizeof(now)); _mix_pool_bytes(utsname(), sizeof(*(utsname()))); - extract_entropy(base_crng.key, sizeof(base_crng.key)); - ++base_crng.generation; - - if (arch_init && trust_cpu && !crng_ready()) { - crng_init = 2; - pr_notice("crng init done (trusting CPU's manufacturer)\n"); - } + if (crng_ready()) + crng_reseed(); + else if (arch_init && trust_cpu) + credit_init_bits(BLAKE2S_BLOCK_SIZE * 8); if (ratelimit_disable) { urandom_warning.interval = 0; @@ -1071,6 +1036,9 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned int nu _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 @@ -1101,7 +1069,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned int nu * Round down by 1 bit on general principles, * and limit entropy estimate to 12 bits. */ - credit_entropy_bits(min_t(unsigned int, fls(delta >> 1), 11)); + credit_init_bits(min_t(unsigned int, fls(delta >> 1), 11)); } void add_input_randomness(unsigned int type, unsigned int code, @@ -1154,18 +1122,15 @@ void rand_initialize_disk(struct gendisk *disk) void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy) { + mix_pool_bytes(buffer, count); + credit_init_bits(entropy); + /* - * Throttle writing if we're above the trickle threshold. - * We'll be woken up again once below POOL_MIN_BITS, when - * the calling thread is about to terminate, or once - * CRNG_RESEED_INTERVAL has elapsed. + * Throttle writing to once every CRNG_RESEED_INTERVAL, unless + * we're not yet initialized. */ - wait_event_interruptible_timeout(random_write_wait, - kthread_should_stop() || - input_pool.entropy_count < POOL_MIN_BITS, - CRNG_RESEED_INTERVAL); - mix_pool_bytes(buffer, count); - credit_entropy_bits(entropy); + if (!kthread_should_stop() && crng_ready()) + schedule_timeout_interruptible(CRNG_RESEED_INTERVAL); } EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); @@ -1177,7 +1142,7 @@ void add_bootloader_randomness(const void *buf, size_t size) { mix_pool_bytes(buf, size); if (trust_bootloader) - credit_entropy_bits(size * 8); + credit_init_bits(size * 8); } EXPORT_SYMBOL_GPL(add_bootloader_randomness); @@ -1193,7 +1158,7 @@ void add_vmfork_randomness(const void *unique_vm_id, size_t size) { add_device_randomness(unique_vm_id, size); if (crng_ready()) { - crng_reseed(true); + crng_reseed(); pr_notice("crng reseeded due to virtual machine fork\n"); } blocking_notifier_call_chain(&vmfork_chain, 0, NULL); @@ -1312,7 +1277,7 @@ static void mix_interrupt_randomness(struct work_struct *work) local_irq_enable(); mix_pool_bytes(pool, sizeof(pool)); - credit_entropy_bits(1); + credit_init_bits(1); memzero_explicit(pool, sizeof(pool)); } @@ -1368,7 +1333,7 @@ static void entropy_timer(struct timer_list *timer) struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer); if (++state->samples == state->samples_per_bit) { - credit_entropy_bits(1); + credit_init_bits(1); state->samples = 0; } } @@ -1468,16 +1433,8 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, static __poll_t random_poll(struct file *file, poll_table *wait) { - __poll_t mask; - poll_wait(file, &crng_init_wait, wait); - poll_wait(file, &random_write_wait, wait); - mask = 0; - if (crng_ready()) - mask |= EPOLLIN | EPOLLRDNORM; - if (input_pool.entropy_count < POOL_MIN_BITS) - mask |= EPOLLOUT | EPOLLWRNORM; - return mask; + return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM; } static int write_pool(const char __user *ubuf, size_t count) @@ -1557,7 +1514,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) switch (cmd) { case RNDGETENTCNT: /* Inherently racy, no point locking. */ - if (put_user(input_pool.entropy_count, p)) + if (put_user(input_pool.init_bits, p)) return -EFAULT; return 0; case RNDADDTOENTCNT: @@ -1567,7 +1524,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) return -EFAULT; if (ent_count < 0) return -EINVAL; - credit_entropy_bits(ent_count); + credit_init_bits(ent_count); return 0; case RNDADDENTROPY: if (!capable(CAP_SYS_ADMIN)) @@ -1581,27 +1538,20 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) retval = write_pool((const char __user *)p, size); if (retval < 0) return retval; - credit_entropy_bits(ent_count); + credit_init_bits(ent_count); return 0; case RNDZAPENTCNT: case RNDCLEARPOOL: - /* - * Clear the entropy pool counters. We no longer clear - * the entropy pool, as that's silly. - */ + /* No longer has any effect. */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; - if (xchg(&input_pool.entropy_count, 0) >= POOL_MIN_BITS) { - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } return 0; case RNDRESEEDCRNG: if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (!crng_ready()) return -ENODATA; - crng_reseed(false); + crng_reseed(); return 0; default: return -EINVAL; @@ -1653,7 +1603,7 @@ const struct file_operations urandom_fops = { * * - write_wakeup_threshold - the amount of entropy in the input pool * below which write polls to /dev/random will unblock, requesting - * more entropy, tied to the POOL_MIN_BITS constant. It is writable + * more entropy, tied to the POOL_INIT_BITS constant. It is writable * to avoid breaking old userspaces, but writing to it does not * change any behavior of the RNG. * @@ -1668,7 +1618,7 @@ const struct file_operations urandom_fops = { #include <linux/sysctl.h> static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ; -static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS; +static int sysctl_random_write_wakeup_bits = POOL_INIT_BITS; static int sysctl_poolsize = POOL_BITS; static u8 sysctl_bootid[UUID_SIZE]; @@ -1724,7 +1674,7 @@ static struct ctl_table random_table[] = { }, { .procname = "entropy_avail", - .data = &input_pool.entropy_count, + .data = &input_pool.init_bits, .maxlen = sizeof(int), .mode = 0444, .proc_handler = proc_dointvec, |