Re: Non-random RDRAND Re: [PATCH] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h

From: Pavel Machek
Date: Fri Aug 16 2019 - 05:07:21 EST

On Thu 2019-08-15 11:12:24, Theodore Y. Ts'o wrote:
> On Thu, Aug 15, 2019 at 01:24:35AM +0200, Pavel Machek wrote:
> > Burn it with fire!
> >
> > I mean... people were afraid RDRAND would be backdoored, and you now
> > confirm ... it indeed _is_ backdoored? /., here's news for you!
> To be fair to AMD, I wouldn't call it a backdoor. Hanlon's razor is
> applicable here:
> "Never attribute to malice that which can be adequately
> explained by neglect."

> (Sometimes other words are used instead of neglect, but i'm trying to
> be nice.)

You are right, I thought it was returning values with low entropy, and
it returns ~0 (so -- really really low entropy :-) and can't be
clasified as a backdoor.

Anyway, AMD is _not_ doing good job right now.

I'd expect:

a) CVE reference

b) real fix; if BIOS can init the rng, so can kernel


(cesky, pictures)

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