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Date:   Wed, 6 Jul 2022 10:55:04 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Heiko Carstens <hca@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] random: remove CONFIG_ARCH_RANDOM and "nordrand"
Message-ID: <YsWiSH4BrY5oNJuM@mit.edu>
References: <20220705190121.293703-1-Jason@zx2c4.com>
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On Tue, Jul 05, 2022 at 09:01:21PM +0200, Jason A. Donenfeld wrote:
> Later the thinking evolved. With a properly designed RNG, using RDRAND
> values alone won't harm anything, even if the outputs are malicious.

I personally think it's totally fine to remove nordrand.  However, the
reason why it was there was that there were some rather extreme
tin-foil-hatters who believed that if (the completely unavailable to
the public for auditing) RDRAND implementation *were* malicious *and*
the microcode had access to the register file and/or the instruction
pipeline, then in theory, a malicious CPU could subvert how the RDRAND
is mixed into the getrandom output to force a particular output.

Personally, I've always considered it to be insane, since a much
easier way to compromise a CPU would be to drop a Minix system hidden
into the CPU running a web server that had massive security bugs in it
that were only discovered years later.  And if you don't trust the CPU
manufacture to that extent, you should probably simply not use CPU's
from that manufacturer.  :-)

							- Ted