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authorJason A. Donenfeld <Jason@zx2c4.com>2022-07-13 17:11:15 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2022-07-16 10:42:12 -0700
commit829d680e82a961c5370d9636130b43009ac36eb8 (patch)
treeb346e911932ceeacb15919a66574a2a70c2ffc8e
parent51a6fa0732d6be6a44e0032752ad2ac10d67c796 (diff)
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 <vladimir.murzin@arm.com> Fixes: 78c768e619fb ("random: vary jitter iterations based on cycle counter speed") Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--drivers/char/random.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index e3dd1dd3dd22..a1af90bacc9f 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();