re: kern/54655: cpu_rng_rdseed() should check support of RDRAND instruction

[matthew green <mrg%eterna.com.au@localhost>]

maya%NetBSD.org@localhost writes:
> On Wed, Oct 30, 2019 at 01:22:44PM +1100, matthew green wrote:
> > rdrand should be retried 10 times in a row and if that
> > fails, we probably should (default) to panicking the system
> > as that indicates a really broken CPU.
> 
> Worth reminding that there are actual CPUs that might fail this test,
> the recent broken Ryzen 3000s.
> 
> Here's one booting netbsd:
> https://dmesgd.nycbug.org/index.cgi?do=view&id=5052
> 
> rnd: source "cpurng" failed continuous-output test.
> rnd: disabling source "cpurng".

actually, that bug won't trip what i'm talking about,
it trips different checks.  :-)

the problem with that bug (that should be fixed in all
systems with modern firmware) was that it gave you
0xffff_ffff_ffff_ffff while saying it was valid.  the
loop i'm talking about is when the says the return is
invalid .. 10 times in a row.


.mrg.