linux-kernel - Re: [PATCH v2 0/5] random,x86,kvm: Add and use MSR_KVM_GET_RNG

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Date:	Wed, 16 Jul 2014 11:16:05 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Bandan Das <bsd@...hat.com>
Cc:	kvm list <kvm@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>,
	"Theodore Ts'o" <tytso@....edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 0/5] random,x86,kvm: Add and use MSR_KVM_GET_RNG_SEED

On Wed, Jul 16, 2014 at 11:02 AM, Bandan Das <bsd@...hat.com> wrote:
> Andy Lutomirski <luto@...capital.net> 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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