diff options
| author | Jason A. Donenfeld <Jason@zx2c4.com> | 2022-07-13 17:11:15 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-07-16 10:42:12 -0700 |
| commit | 829d680e82a961c5370d9636130b43009ac36eb8 (patch) | |
| tree | b346e911932ceeacb15919a66574a2a70c2ffc8e | |
| parent | 51a6fa0732d6be6a44e0032752ad2ac10d67c796 (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.c | 2 |
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(); |