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Subject[PATCH v2 3/5] random: add back async readiness notifier
Date
This is required by vsprint, because it can't do things synchronously
from hardirq context, and it will be useful for an EFI notifier as well.
I didn't initially want to do this, but with two potential consumers
now, it seems worth it.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
drivers/char/random.c | 20 ++++++++++++++++++++
include/linux/random.h | 1 +
2 files changed, 21 insertions(+)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 65ee69896967..1185fe11b719 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -84,6 +84,7 @@ 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 ATOMIC_NOTIFIER_HEAD(random_ready_notifier);

/* Control how we warn userspace. */
static struct ratelimit_state urandom_warning =
@@ -140,6 +141,24 @@ int wait_for_random_bytes(void)
}
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.
+ */
+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", \
@@ -697,6 +716,7 @@ static void __cold _credit_init_bits(size_t 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");
diff --git a/include/linux/random.h b/include/linux/random.h
index 579117d83eb8..b1a34181eed6 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -120,6 +120,7 @@ void __init random_init_early(const char *command_line);
void __init random_init(void);
bool rng_is_initialized(void);
int wait_for_random_bytes(void);
+int execute_with_initialized_rng(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. */
--
2.38.1
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