linux-kernel - Re: is "premature next" a real world rng concern, or just an academic exercise?

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Message-ID: <Yn34YWhH1nSa8O8K@owl.dominikbrodowski.net>
Date:   Fri, 13 May 2022 08:19:13 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Thomas Ristenpart <ristenpart@...nell.edu>,
        Yevgeniy Dodis <dodis@...nyu.edu>, tytso <tytso@....edu>,
        Nadia Heninger <nadiah@...ucsd.edu>,
        Noah Stephens-Dawidowitz <noahsd@...il.com>,
        Stefano Tessaro <tessaro@...washington.edu>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "D. J. Bernstein" <djb@...yp.to>,
        "jeanphilippe.aumasson@...il.com" <jeanphilippe.aumasson@...il.com>,
        "jann@...jh.net" <jann@...jh.net>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Peter Schwabe <peter@...ptojedi.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: is "premature next" a real world rng concern, or just an
 academic exercise?

Am Thu, May 12, 2022 at 01:47:06PM +0200 schrieb Jason A. Donenfeld:
> But on the other hand, it appears that none of us really thinks that
> premature next is a real problem worth complicating designs over. So
> maybe we can just say that it is nice when the silicon in one way or
> another helps with premature next, but maybe not an explicit must have.
> So where does that leave us?
> 
> - Systems with RDSEED/RDRAND don't have premature next, due to the above
>   KDF salt. This is probably the majority of systems out there these
>   days. This also applies to the sleep resumption notification (and the
>   vmgenid one), and I suspect that most systems with S3 or S0ix or
>   whatever else these days also probably have RDRAND.

... and most of these systems have TPM chips with a RNG, which is (alas)
usually only used at system startup, as that hw_rng device sets its quality
to 0 (meaning untrusted). So there's also room for improvement involving
these hw rng devices.

Thanks,
	Dominik