Re: [PATCH v2 0/5] random,x86,kvm: Add and use MSR_KVM_GET_RNG_SEED

From: Andy Lutomirski
Date: Wed Jul 16 2014 - 14:16:34 EST


On Wed, Jul 16, 2014 at 11:02 AM, Bandan Das <bsd@xxxxxxxxxx> wrote:
> Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes:
>
>> virtio-rng is both too complicated and insufficient for initial rng
>> seeding. It's far too complicated to use for KASLR or any other
>> early boot random number needs. It also provides /dev/random-style
>> bits, which means that making guest boot wait for virtio-rng is
>> unacceptably slow, and doing it asynchronously means that
>> /dev/urandom might be predictable when userspace starts.
>>
>> This introduces a very simple synchronous mechanism to get
>> /dev/urandom-style bits.
>
> Whoa! the cover letter seems more like virtio-rng bashing rather than
> introduction to the patchset (and/or it's advantages over existing methods)
> :) That's ok though I guess, these won't be in the commit log.
>

Yeah, sorry -- I figured that the biggest objection would be "just use
virtio-rng".

I'll send a v3 later today -- there's a trivial bisectability bug in
this version.

--Andy

>> I sent the corresponding kvm-unit-tests and qemu changes separately.
>>
>> There's room for bikeshedding on the same arch_get_slow_rng_u64. I
>> considered arch_get_rng_seed_u64, but that could be confused with
>> arch_get_random_seed_long, which is not interchangeable.
>>
>> Changes from v1:
>> - Split patches 2 and 3
>> - Log all arch sources in init_std_data
>> - Fix the 32-bit kaslr build
>>
>> Andy Lutomirski (5):
>> x86,kvm: Add MSR_KVM_GET_RNG_SEED and a matching feature bit
>> random,x86: Add arch_get_slow_rng_u64
>> random: Seed pools from arch_get_slow_rng_u64 at startup
>> random: Log how many bits we managed to seed with in init_std_data
>> x86,kaslr: Use MSR_KVM_GET_RNG_SEED for KASLR if available
>>
>> Documentation/virtual/kvm/cpuid.txt | 3 +++
>> arch/x86/Kconfig | 4 ++++
>> arch/x86/boot/compressed/aslr.c | 27 +++++++++++++++++++++++++++
>> arch/x86/include/asm/archslowrng.h | 30 ++++++++++++++++++++++++++++++
>> arch/x86/include/asm/processor.h | 21 ++++++++++++++++++---
>> arch/x86/include/uapi/asm/kvm_para.h | 2 ++
>> arch/x86/kernel/kvm.c | 22 ++++++++++++++++++++++
>> arch/x86/kvm/cpuid.c | 3 ++-
>> arch/x86/kvm/x86.c | 4 ++++
>> drivers/char/random.c | 20 ++++++++++++++++++--
>> include/linux/random.h | 9 +++++++++
>> 11 files changed, 139 insertions(+), 6 deletions(-)
>> create mode 100644 arch/x86/include/asm/archslowrng.h



--
Andy Lutomirski
AMA Capital Management, LLC
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