Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy

From	Theodore Ts'o <tytso@mit.edu>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy
Date	2016-08-11 01:50 +0200
Message-ID	<s4Lq1-3su-1@gated-at.bofh.it> (permalink)
References	(3 earlier) <s3MxQ-6io-31@gated-at.bofh.it> <s3WGR-4qo-5@gated-at.bofh.it> <s48RH-3Wx-29@gated-at.bofh.it> <s4dRo-752-19@gated-at.bofh.it> <s4fTc-bN-27@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Tue, Aug 09, 2016 at 02:04:44PM +0000, Jason Cooper wrote:
> 
> iiuc, Ted, you're saying using the hw_random framework would be
> disasterous because despite most drivers having a default quality of 0,
> rngd assumes 1 bit of entropy for every bit read?

Sorry, what I was trying to say (but failed) was that bypassing the
hwrng framework and injecting entropy directly the entropy pool was
disatrous.

> Thankfully, most hw_random drivers don't set the quality.  So unless the
> user sets the default_quality param, it's zero.

The fact that this is "most" and not "all" does scare me a little.

As far as I'm concerned *all* hw_random drivers should set quality to
zero, since it should be up to the system administrator.  Perhaps the
one exception is virtio_rng, since if you don't trust the hypvervisor,
the security of the VM is hopeless.  That being said, I have seen
configurations of KVM which use:

	-object rng-random,filename=/dev/urandom,id=rng0 \
	-device virtio-rng-pci,rng=rng0

Which is somewhat non-ideal.  (Try running od -x /dev/random on such a
guest system....)

					- Ted

Thread

[RFC][PATCH] RANDOM: ATH9K RNG delivers zero bits of entropy Stephan Mueller <smueller@chronox.de> - 2016-08-05 17:10 +0200
  Re: [RFC][PATCH] RANDOM: ATH9K RNG delivers zero bits of entropy Stephan Mueller <smueller@chronox.de> - 2016-08-06 22:10 +0200
    Re: [RFC][PATCH] RANDOM: ATH9K RNG delivers zero bits of entropy Jason Cooper <jason@lakedaemon.net> - 2016-08-06 22:20 +0200
  Re: [RFC][PATCH] RANDOM: ATH9K RNG delivers zero bits of entropy Jason Cooper <jason@lakedaemon.net> - 2016-08-06 22:10 +0200
  [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Stephan Mueller <smueller@chronox.de> - 2016-08-07 11:40 +0200
    RE: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy "Pan, Miaoqing" <miaoqing@qti.qualcomm.com> - 2016-08-08 04:10 +0200
      Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Stephan Mueller <smueller@chronox.de> - 2016-08-08 08:50 +0200
        Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Jason Cooper <jason@lakedaemon.net> - 2016-08-08 19:40 +0200
          Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Jason Cooper <jason@lakedaemon.net> - 2016-08-09 00:10 +0200
          RE: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy "Pan, Miaoqing" <miaoqing@qti.qualcomm.com> - 2016-08-09 08:40 +0200
            Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Theodore Ts'o <tytso@mit.edu> - 2016-08-09 14:00 +0200
              Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Jason Cooper <jason@lakedaemon.net> - 2016-08-09 16:10 +0200
                Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Theodore Ts'o <tytso@mit.edu> - 2016-08-11 01:50 +0200
                Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Jason Cooper <jason@lakedaemon.net> - 2016-08-14 20:20 +0200
      Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Kalle Valo <kvalo@codeaurora.org> - 2016-08-15 13:10 +0200

csiph-web