Bug: jitter entropy health test unreliable on Rpi 4 (arm64)

[Stephan Mueller]

Am Freitag, 21. Juli 2023, 14:28:29 CEST schrieb Stefan Wahren:

Hi Stefan,

sorry for the delay.

> Hi,
> 
> i recently tested Linux 6.5-rc2 on the Raspberry Pi 4 (arm64/defconfig)
> and noticed the following message:
> 
> [    0.136349] jitterentropy: Initialization failed with host not
> compliant with requirements: 9
> 
> Since Linux 6.5-rc2 this message occurs in around about 1 of 2 cases
> during boot. In Linux 6.4 this message i never saw this message.

This system has not that much entropy. A short-term fix would be to set the 
oversampling rate to a higher value than 1, the current value.

See jent_entropy_collector_alloc:

        /* verify and set the oversampling rate */
        if (osr == 0)
                osr = 1; /* minimum sampling rate is 1 */

The osr could be set to 3, for example. This makes the Jitter RNG slower, but 
it can now handle lower-entropy environments.

Let me see how this can be fixed.

Thanks for the report.

Ciao
Stephan