| Message ID | 20220713151115.1014188-1-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | random: cap jitter samples per bit to factor of HZ | expand |
On 7/13/22 16:11, Jason A. Donenfeld wrote: > 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> > --- > Vladimir - Can you let me know if this appears to fix the issue you're > seeing? -Jason Works for me, thanks! :) > > 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 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(); FWIW Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> Cheers Vladimir
Hi Vladmir, On Wed, Jul 13, 2022 at 04:52:20PM +0100, Vladimir Murzin wrote: > On 7/13/22 16:11, Jason A. Donenfeld wrote: > > Vladimir - Can you let me know if this appears to fix the issue you're > > seeing? -Jason > > Works for me, thanks! :) > Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> Thanks for testing. I'll push this out to Linus probably tomorrow. (Though I noticed that Linus is in the CC for this thread already, and he's been on a patch picking spree as of late, so in case he happens to be following along, fell free to pick away. Otherwise I'll send a pull not before long.) Jason
On Wed, Jul 13, 2022 at 9:22 AM Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > Thanks for testing. I'll push this out to Linus probably tomorrow. > > (Though I noticed that Linus is in the CC for this thread already, and > he's been on a patch picking spree as of late, so in case he happens to > be following along, fell free to pick away. Otherwise I'll send a pull > not before long.) Well, the "probably tomorrow" didn't happen, so yes, I've just picked it up directly. Linus
Hey Linus, On Sat, Jul 16, 2022 at 10:45:24AM -0700, Linus Torvalds wrote: > On Wed, Jul 13, 2022 at 9:22 AM Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > > > Thanks for testing. I'll push this out to Linus probably tomorrow. > > > > (Though I noticed that Linus is in the CC for this thread already, and > > he's been on a patch picking spree as of late, so in case he happens to > > be following along, fell free to pick away. Otherwise I'll send a pull > > not before long.) > > Well, the "probably tomorrow" didn't happen, so yes, I've just picked > it up directly. Oh, okay. Something came up on Thursday, and I just sat down (on the train back home) to do this now. So I didn't forget! But thanks for taking it nonetheless. Jason
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();
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> --- Vladimir - Can you let me know if this appears to fix the issue you're seeing? -Jason drivers/char/random.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)