From d6ce4bf084c3e7ef70f782d6823a18a9097c930a Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 13 Jul 2022 17:11:15 +0200 Subject: [PATCH] random: cap jitter samples per bit to factor of HZ Currently the jitter mechanism will require two timer ticks per iteration, and it requires N iterations per bit. This N is determined with a small measurement, and if it's too big, it won't waste time with jitter entropy because it'd take too long or not have sufficient entropy anyway. With the current max N of 32, there are large timeouts on systems with a small CONFIG_HZ. Rather than set that maximum to 32, instead choose a factor of CONFIG_HZ. In this case, 1/30 seems to yield sane values for different configurations of CONFIG_HZ. Reported-by: Vladimir Murzin Fixes: 2fc3e113e981 ("random: vary jitter iterations based on cycle counter speed") Signed-off-by: Jason A. Donenfeld Tested-by: Vladimir Murzin Signed-off-by: Linus Torvalds --- drivers/char/random.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index e3dd1dd3dd226..a1af90bacc9f8 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1174,7 +1174,7 @@ static void __cold entropy_timer(struct timer_list *timer) */ static void __cold try_to_generate_entropy(void) { - enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = 32 }; + enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 30 }; struct entropy_timer_state stack; unsigned int i, num_different = 0; unsigned long last = random_get_entropy(); -- 2.39.5