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Subject: Re: Linux 5.3-rc8
To:     Lennart Poettering <mzxreary@0pointer.de>, Willy Tarreau <w@1wt.eu>
Cc:     "Theodore Y. Ts'o" <tytso@mit.edu>,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Ahmed S. Darwish" <darwish.07@gmail.com>,
        Vito Caputo <vcaputo@pengaru.com>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Jan Kara <jack@suse.cz>, Ray Strode <rstrode@redhat.com>,
        William Jon McCann <mccann@jhu.edu>,
        zhangjs <zachary@baishancloud.com>, linux-ext4@vger.kernel.org,
        lkml <linux-kernel@vger.kernel.org>
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 <20190917052438.GA26923@1wt.eu> <2508489.jOnZlRuxVn@merkaba>
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 <20190917162137.GA27921@1wt.eu> <20190917171328.GA31798@gardel-login>
 <20190917172929.GD27999@1wt.eu> <20190918133806.GA32346@gardel-login>
From:   "Alexander E. Patrakov" <patrakov@gmail.com>
Message-ID: <dde9545e-66a7-f9cc-7b03-63517c4f8655@gmail.com>
Date:   Wed, 18 Sep 2019 18:59:31 +0500
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18.09.2019 18:38, Lennart Poettering =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
> On Di, 17.09.19 19:29, Willy Tarreau (w@1wt.eu) wrote:
>=20
>>> What do you expect these systems to do though?
>>>
>>> I mean, think about general purpose distros: they put together live
>>> images that are supposed to work on a myriad of similar (as in: same
>>> arch) but otherwise very different systems (i.e. VMs that might lack
>>> any form of RNG source the same as beefy servers with muliple sources=

>>> the same as older netbooks with few and crappy sources, ...). They ca=
n't
>>> know what the specific hw will provide or won't. It's not their
>>> incompetence that they build the image like that. It's a common, very=

>>> common usecase to install a system via SSH, and it's also very common=

>>> to have very generic images for a large number varied systems to run
>>> on.
>>
>> I'm totally file with installing the system via SSH, using a temporary=

>> SSH key. I do make a strong distinction between the installation phase=

>> and the final deployment. The SSH key used *for installation* doesn't
>> need to the be same as the final one. And very often at the end of the=

>> installation we'll have produced enough entropy to produce a correct
>> key.
>=20
> That's not how systems are built today though. And I am not sure they
> should be. I mean, the majority of systems at this point probably have
> some form of hardware (or virtualized) RNG available (even raspi has
> one these days!), so generating these keys once at boot is totally
> OK. Probably a number of others need just a few seconds to get the
> entropy needed, where things are totally OK too. The only problem is
> systems that lack any reasonable source of entropy and where
> initialization of the pool will take overly long.
>=20
> I figure we can reduce the number of systems where entropy is scarce
> quite a bit if we'd start crediting entropy by default from various hw
> rngs we currently don't credit entropy for. For example, the TPM and
> older intel/amd chipsets. You currently have to specify
> rng_core.default_quality=3D1000 on the kernel cmdline to make them
> credit entropy. I am pretty sure this should be the default now, in a
> world where CONFIG_RANDOM_TRUST_CPU=3Dy is set anyway. i.e. why say
> RDRAND is fine but those chipsets are not? That makes no sense to me.
>=20
> I am very sure that crediting entropy to chipset hwrngs is a much
> better way to solve the issue on those systems than to just hand out
> rubbish randomness.

Very well said. However, 1000 is more than the hard-coded quality of=20
some existing rngs, and so would send a misleading message that they are =

somehow worse. I would suggest case-by-case reevaluation of all existing =

hwrng drivers by their maintainers, and then setting the default to=20
something like 899, so that evaluated drivers have priority.

--=20
Alexander E. Patrakov


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