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random: remove mostly unused async readiness notifier

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The register_random_ready_notifier() notifier is somewhat complicated,
and was already recently rewritten to use notifier blocks. It is only
used now by one consumer in the kernel, vsprintf.c, for which the async
mechanism is really overly complex for what it actually needs. This
commit removes register_random_ready_notifier() and unregister_random_
ready_notifier(), because it just adds complication with little utility,
and changes vsprintf.c to just check on `!rng_is_initialized() &&
!rng_has_arch_random()`, which will eventually be true. Performance-
wise, that code was already using a static branch, so there's basically
no overhead at all to this change.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Petr Mladek <pmladek@suse.com> # for vsprintf.c
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2022-05-15 15:06:18 +02:00
parent 248561ad25
commit 6701de6c51
3 changed files with 22 additions and 94 deletions
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48
drivers/char/random.c
View file

@ -84,8 +84,6 @@ static DEFINE_STATIC_KEY_FALSE(crng_is_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 =
@ -142,51 +140,6 @@ int wait_for_random_bytes(void)
}
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", \
@ -775,7 +728,6 @@ static void __cold _credit_init_bits(size_t bits)
if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
execute_in_process_context(crng_set_ready, &set_ready);
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
pr_notice("crng init done\n");

2
include/linux/random.h
View file

@ -78,8 +78,6 @@ int __init random_init(const char *command_line);
bool rng_is_initialized(void);
bool rng_has_arch_random(void);
int wait_for_random_bytes(void);
int register_random_ready_notifier(struct notifier_block *nb);
int unregister_random_ready_notifier(struct notifier_block *nb);
/* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes).
* Returns the result of the call to wait_for_random_bytes. */

66
lib/vsprintf.c
View file

@ -750,60 +750,38 @@ static int __init debug_boot_weak_hash_enable(char *str)
}
early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable);
static DEFINE_STATIC_KEY_TRUE(not_filled_random_ptr_key);
static siphash_key_t ptr_key __read_mostly;
static DEFINE_STATIC_KEY_FALSE(filled_random_ptr_key);
static void enable_ptr_key_workfn(struct work_struct *work)
{
get_random_bytes(&ptr_key, sizeof(ptr_key));
/* Needs to run from preemptible context */
static_branch_disable(&not_filled_random_ptr_key);
static_branch_enable(&filled_random_ptr_key);
}
static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
static int fill_random_ptr_key(struct notifier_block *nb,
unsigned long action, void *data)
{
/* This may be in an interrupt handler. */
queue_work(system_unbound_wq, &enable_ptr_key_work);
return 0;
}
static struct notifier_block random_ready = {
.notifier_call = fill_random_ptr_key
};
static int __init initialize_ptr_random(void)
{
int ret;
/* Don't bother waiting for RNG to be ready if RDRAND is mixed in already. */
if (rng_has_arch_random()) {
enable_ptr_key_workfn(&enable_ptr_key_work);
return 0;
}
ret = register_random_ready_notifier(&random_ready);
if (!ret) {
return 0;
} else if (ret == -EALREADY) {
/* This is in preemptible context */
enable_ptr_key_workfn(&enable_ptr_key_work);
return 0;
}
return ret;
}
early_initcall(initialize_ptr_random);
/* Maps a pointer to a 32 bit unique identifier. */
static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
{
static siphash_key_t ptr_key __read_mostly;
unsigned long hashval;
if (static_branch_unlikely(&not_filled_random_ptr_key))
return -EAGAIN;
if (!static_branch_likely(&filled_random_ptr_key)) {
static bool filled = false;
static DEFINE_SPINLOCK(filling);
static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
unsigned long flags;
if (!system_unbound_wq ||
(!rng_is_initialized() && !rng_has_arch_random()) ||
!spin_trylock_irqsave(&filling, flags))
return -EAGAIN;
if (!filled) {
get_random_bytes(&ptr_key, sizeof(ptr_key));
queue_work(system_unbound_wq, &enable_ptr_key_work);
filled = true;
}
spin_unlock_irqrestore(&filling, flags);
}
#ifdef CONFIG_64BIT
hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);