[BUG] Non working HWRNG on AMD Ryzen 5 5500GT

["Diederik de Haas" <didi.debian@cknow.org>]

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Hi,

I recently bought an Asus ROG STRIX B550-F GAMING MB with an
AMD Ryzen 5 5500GT CPU (and installed the latest BIOS: 3607).
I'm running Debian Testing/Sid on it with kernel 6.9 and now 6.10
and it seems to work great.
I've been doing some (unrelated) tests with `rngtest` from the
`rng-tools5` package and wondered how it would fare on my AMD CPU.

And I found out it doesn't work at all!
But on another system I have (Asus ROG CROSSHAIR VII HERO MB +
AMD Ryzen 1800X CPU) it works absolutely fine.

# dmesg | grep ccp
[    5.399853] ccp 0000:07:00.2: ccp: unable to access the device: you might
be running a broken BIOS.
[    5.401031] ccp 0000:07:00.2: tee enabled
[    5.401113] ccp 0000:07:00.2: psp enabled

Found an article [1] which could be relevant and downloaded and ran the
accompanying test program (written by Jason Donenfeld):
# ./amd-rdrand-bug
Your RDRAND() does not have the AMD bug.
# ./test-rdrand
RDRAND() = 0x47c993c0
RDRAND() = 0xec7c697d
... (more seemingly random numbers)
RDRAND() = 0xba858101

I tried it with the latest microcode dd 2024-07-10, but that didn't make
a difference.

So I'd like to know if this may actually be a bug on the kernel side.

Happy to provide additional information or run tests or try patches.

Cheers,
  Diederik

[1] https://arstechnica.com/gadgets/2019/10/how-a-months-old-amd-microcode-bug-destroyed-my-weekend/

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