linux-kernel - Re: [PATCH v5 0/5] random,x86,kvm: Rework arch RNG seeds and get some from kvm

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Date:	Wed, 13 Aug 2014 09:13:42 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"Theodore Ts'o" <tytso@....edu>, "H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	kvm list <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Bandan Das <bsd@...hat.com>, Andrew Honig <ahonig@...gle.com>
Subject: Re: [PATCH v5 0/5] random,x86,kvm: Rework arch RNG seeds and get some
 from kvm

On Wed, Aug 13, 2014 at 7:32 AM, Theodore Ts'o <tytso@....edu> wrote:
> On Wed, Aug 13, 2014 at 12:48:41AM -0700, H. Peter Anvin wrote:
>> The proposed arch_get_rng_seed() is not really what it claims to be; it
>> most definitely does not produce seed-grade randomness, instead it seems
>> to be an arch function for best-effort initialization of the entropy
>> pools -- which is fine, it is just something quite different.
>
> Without getting into an argument about which definition of "seed" is
> correct --- it's certainly confusing and different form the RDSEED
> usage of the word "seed".
>
> Do we expect that anyone else besides arch_get_rnd_seed() would
> actually want to use it?

If you mean random.c instead of arch_get_rnd_seed, then I don't expect
there to be other users.  Aside from the "best-effort" bit causing
this to be basically useless on old bare metal, the interface is
really awkward for anything other than the use in random.c.

> I'd argue no; we want the rest of the kernel
> to either use get_random_bytes() or prandom_u32().  Given that, maybe
> we should just call it arch_random_init(), and expect that the only
> user of this interface would be drivers/char/random.c?

Sounds good to me.

FWIW, I'd like to see a second use added in random.c: I think that we
should do this, or even all of init_std_data, on resume from suspend
and especially on resume from hibernate / kexec.

--Andy
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