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

Andy Lutomirski
2014-09-19T17:39:58Z

On Fri, Sep 19, 2014 at 10:36 AM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 09/19/2014 10:21 AM, Andy Lutomirski wrote:
>>>
>>> There is a huge disadvantage to the fact that CPUID is a user space
>>> instruction, though.
>>
>> We can always make cpuid on the leaf in question return all zeros if CPL > 0.
>>
>
> Not sure that is better...

It's better than #GP...

This is why I prefer rdmsr: the privilege semantics are already
appropriate. Also, I wouldn't be surprised if shoehorning
non-constant results into cpuid implementations might be awkward for
some hypervisors.

--Andy