Messages in this thread | | | Subject | Re: [PATCH] random: Add "initialized" variable to proc | From | "H. Peter Anvin" <> | Date | Wed, 30 Apr 2014 21:05:00 -0700 |
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Qemu is using /dev/random because there is no point in emptily feeding one prng from another.
Giving the guest a seed would be highly useful, though. There are a number of ways to do that; changing the boot protocol is probably only useful if Qemu itself bouts the kernel as opposed to an in-VM bootloader.
That leaves several options other than virtio: I/O port, magic number in memory, CPUID, MSR, or even emulating RDRAND/RDSEED in the VMM.
On April 30, 2014 7:06:27 PM PDT, Theodore Ts'o <tytso@mit.edu> wrote: >On Wed, Apr 30, 2014 at 01:52:35PM -0700, Andy Lutomirski wrote: >> >> 1. It simply doesn't work on my system. In particular, it never >returns >> entropy. It just blocks forever. > >Why? Is this a bug in qemu? The host OS? The guest OS? It is qemu >trying to use /dev/random instead of /dev/urandom? Any thing else? > >> 3. There should be a way to provide some entropy-free >cryptographically >> secure data, too. Regardless of the speed of the hosts's >/dev/random, >> the guest should start with at least 256 bits of cryptographically >> secure seed material IMO. > >Well, the simplest way to do this is to pass it in via the command >line, and then have the the kernel make sure it gets obscured so it's >not exposed via /proc/cmdline. > >Otherwise we would have to define an extension where we pass 32 bytes >or so after the boot command line. But the downside of doing that is >we would have to modify every single architecture to define where >those 32 bytes could be found. > >Aside from passing it on the command line as being a bit grotty, the >other big problem this is that some architectures only have 256 bytes >of command line, and if we use a base 64 encoding, 256 bits will take >43 characters. Not a problem on x86, and it seems rather unlikely >that people would want to virtualize a m68k or avr32 CPU. It just >feels really unclean. > >I've cc'ed Peter Anvin for his opinion about extending Linux boot >parameter protocol. I agree it would be a lot simpler and easier to >enable things like Kernel ASLR with real randomness on guest OS's if >we didn't have to erect the whole virtio-pci infrastructure during >early boot. :-) > > -Ted
-- Sent from my mobile phone. Please pardon brevity and lack of formatting.
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