On 07/22/2014 02:10 PM, Andy Lutomirski wrote: > On Tue, Jul 22, 2014 at 2:08 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: >> On 07/22/2014 02:04 PM, Andy Lutomirski wrote: >>> >>> Just to check: do you mean the RDRAND is very likely to work (i.e. >>> arch_get_random_long will return true) or that RDRAND will actually >>> reseed several times during initialization? >>> >> >> I mean that RDRAND will actually reseed several times during >> initialization. The documented architectural limit is actually >> extremely conservative. >> >> Either way, it isn't really different from seeding from a VM hosts >> /dev/urandom... > > Sure it is. The VM host's /dev/urandom makes no guarantee (or AFAIK > even any particular effort) to reseed such that the output has some > minimum entropy per bit, so there would be no point to reading extra > data from it. Depends on what you define as "extra data". If the data pulled is less than the size of the output pool, it *may* be fully entropic. (Fun fact: it may even have been fully entropic at the time you pull it, but then turn out not to be later because *another* process consumed data from /dev/urandom without adequate reseeding.) > Anyway, I'd be willing to drop the conservative RDRAND logic, but I > *still* think that arch_get_rng_seed is a much better interface than > arch_get_slow_rng_u64. That I will leave up to you and Ted. -hpa -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
