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

[Bandan Das]

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.

> 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
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