Re: Standardizing an MSR or other hypercall to get an RNG seed?

H. Peter Anvin
2014-09-22T23:01:28Z

Not really, no.

Sent from my tablet, pardon any formatting problems.

> On Sep 22, 2014, at 06:31, Christopher Covington <cov@codeaurora.org> wrote:
>
>> On 09/19/2014 05:46 PM, H. Peter Anvin wrote:
>> On 09/19/2014 01:46 PM, Andy Lutomirski wrote:
>>>>
>>>> However, it sounds to me that at least for KVM, it is very easy just to emulate the RDRAND instruction. The hypervisor would report to the guest that RDRAND is supported in CPUID and the emulate the instruction when guest executes it. KVM already traps guest #UD (which would occur if RDRAND executed while it is not supported) - so this scheme wouldn’t introduce additional overhead over RDMSR.
>>>
>>> Because then guest user code will think that rdrand is there and will
>>> try to use it, resulting in abysmal performance.
>>
>> Yes, the presence of RDRAND implies a cheap and inexhaustible entropy
>> source.
>
> A guest kernel couldn't make it look like RDRAND is not present to guest
> userspace?
>
> Christopher
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> hosted by the Linux Foundation.
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org