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

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Message-ID: <20190816090713.GA17833@amd>
Date:   Fri, 16 Aug 2019 11:07:13 +0200
From:   Pavel Machek <pavel@....cz>
To:     "Theodore Y. Ts'o" <tytso@....edu>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        nhorman@...driver.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Chen Yu <yu.c.chen@...el.com>, Jonathan Corbet <corbet@....net>
Subject: Re: Non-random RDRAND Re: [PATCH] x86/CPU/AMD: Clear RDRAND CPUID
 bit on AMD family 15h/16h

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

									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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