Commit 745558f9 authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Jason A. Donenfeld
Browse files

random: use hwgenerator randomness more frequently at early boot 



Mix in randomness from hw-rng sources more frequently during early
boot, approximately once for every rng reseed.

Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
parent cd4f24ae

drivers/char/random.c

+10 −12
Original line number Diff line number Diff line
@@ -260,25 +260,23 @@ 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 is needed. This happens if the last reseeding

 * was CRNG_RESEED_INTERVAL ago, or during early boot, at an interval

 * Return the interval until the next reseeding, which is normally

 * CRNG_RESEED_INTERVAL, but during early boot, it is at an interval

 * proportional to the uptime.

 */

static bool crng_has_old_seed(void)

static unsigned int crng_reseed_interval(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,

			return max_t(unsigned int, CRNG_RESEED_START_INTERVAL,

				     (unsigned int)uptime / 2 * HZ);

	}

	return time_is_before_jiffies(READ_ONCE(base_crng.birth) + interval);

	return CRNG_RESEED_INTERVAL;

}



/*
@@ -320,7 +318,7 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], 
	 * 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()))

	if (unlikely(time_is_before_jiffies(READ_ONCE(base_crng.birth) + crng_reseed_interval())))

		crng_reseed();



	local_lock_irqsave(&crngs.lock, flags);
@@ -866,11 +864,11 @@ void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy) 
	credit_init_bits(entropy);



	/*

	 * Throttle writing to once every CRNG_RESEED_INTERVAL, unless

	 * we're not yet initialized.

	 * Throttle writing to once every reseed interval, unless we're not yet

	 * initialized.

	 */

	if (!kthread_should_stop() && crng_ready())

		schedule_timeout_interruptible(CRNG_RESEED_INTERVAL);

		schedule_timeout_interruptible(crng_reseed_interval());

}

EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);