[PATCH v2 3/5] random: add back async readiness notifier

Jason A. Donenfeld
2022-11-18T13:34:17Z

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