linux-kernel - Re: [PATCH v3 2/5] random,x86: Add arch_get_slow_rng

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Date:	Thu, 17 Jul 2014 14:39:42 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Andy Lutomirski <luto@...capital.net>,
	kvm list <kvm@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	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>, hannes@...essinduktion.org
Subject: Re: [PATCH v3 2/5] random,x86: Add arch_get_slow_rng_u64

On 07/17/2014 12:59 AM, H. Peter Anvin wrote:
> On 07/16/2014 03:40 PM, Andy Lutomirski wrote:
>> On Wed, Jul 16, 2014 at 3:13 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>> My personal preference is to defer this until some user shows up.  I
>>> think that even this would be too complicated for KASLR, which is the
>>> only extremely early-boot user that I found.
>>>
>>> Hmm.  Does the prandom stuff want to use this?
>>
>> prandom isn't even using rdrand.  I'd suggest fixing this separately,
>> or even just waiting until someone goes and deletes prandom.
>
> prandom is exactly the opposite; it is designed for when we need
> possibly low quality random numbers very quickly.  RDRAND is actually
> too slow.

Yep, prandom() is quite heavily used in the network stack where it's
traded for speed.
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