linux-kernel - Re: [PATCH] random: add a config option to trust the CPU's hwrng

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Message-ID: <20180718142625.GA5942@thunk.org>
Date:   Wed, 18 Jul 2018 10:26:25 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Yann Droneaud <ydroneaud@...eya.com>
Cc:     linux-crypto@...r.kernel.org,
        Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
        labbott@...hat.com
Subject: Re: [PATCH] random: add a config option to trust the CPU's hwrng

On Wed, Jul 18, 2018 at 09:22:13AM +0200, Yann Droneaud wrote:
> 
> The text message should explain this is only relevant during
> initialization / early boot.
> 
> The config option name should state this.

There are other workarounds for hangs that happen after initialization
/ early boot, yes.  They are of varying levels of quality / safely,
but that's neither here nor there.

However, enabling config option means that the CRNG will be
initialized with potentially information available to the CPU
manufacturer and/or Nation States, and this persists *after*
initialization / early boot.  So to say, "we're perfectly safe after
we leave initialization / early boot" is not true.

So I'd much rather make it clear that we are trusting the CPU
manufacturer far more than just during early boot.

Cheers,

					- Ted