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* CAAM RNG trouble
@ 2020-12-14 19:00 Lucas Stach
  2021-03-02 17:33 ` Horia Geantă
  0 siblings, 1 reply; 10+ messages in thread
From: Lucas Stach @ 2020-12-14 19:00 UTC (permalink / raw)
  To: Horia Geantă, Aymen Sghaier, Alexandru Porosanu; +Cc: linux-crypto, kernel

Hi all,

I've been looking into a CAAM RNG issue for a while, where I could need
some input from people knowing the CAAM hardware better than I do.
Basically the issue is that on some i.MX6 units the RNG functionality
sometimes fails with this error:
caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error.

I can tell that it is related to the entropy delay. On all failing
units the RNG4 gets instantiated with the default entropy delay of
3200. If I dial up the delay to 3600 or 4000 the RNG works reliably. As
a negative test I changed the initial delay to 400. With this change
all units are able to successfully instantiate the RNG handles at an
entropy delay of 2000 or 2400, but then reliably fail at getting random
data with the error shown above. I guess the issue is related to
prediction resistance on the handles, which causes the PRNG to be re-
seeded from the TRNG fairly often.

Now I don't have a good idea on how to arrive at a reliably working
entropy delay setting, as apparently the simple "are we able to
instantiate the handle" check is not enough to actually guarantee a
working RNG setup. Any suggestions?

Regards,
Lucas


^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2022-01-24 12:25 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-12-14 19:00 CAAM RNG trouble Lucas Stach
2021-03-02 17:33 ` Horia Geantă
2021-03-03  0:37   ` Robert Hancock
2021-11-12 15:27     ` [RFC PATCH] crypto: caam - restore retry count after HW RNG failure Michal Vokáč
     [not found]       ` <DU2PR04MB863088F218774551FA254EB795539@DU2PR04MB8630.eurprd04.prod.outlook.com>
2022-01-13  7:23         ` [EXT] " Gaurav Jain
2022-01-17 14:08           ` Petr Benes
2022-01-18  9:04             ` Gaurav Jain
2022-01-20  9:59           ` Petr Benes
2022-01-24  7:04             ` Gaurav Jain
2022-01-24 12:25               ` Petr Benes

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