linux-kernel - Re: [PATCH v3 0/5] ARM: arm64: Add SMCCC TRNG entropy service

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Date:   Fri, 13 Nov 2020 23:54:30 +0000
From:   André Przywara <andre.przywara@....com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Marc Zyngier <maz@...nel.org>, Theodore Ts'o <tytso@....edu>,
        Sudeep Holla <sudeep.holla@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/5] ARM: arm64: Add SMCCC TRNG entropy service

On 13/11/2020 23:05, Ard Biesheuvel wrote:
> On Fri, 13 Nov 2020 at 19:24, Andre Przywara <andre.przywara@....com> wrote:
>>
>> Hi,
>>
>> an update to v2 with some fixes and a few tweaks. Ard's patch [1] should
>> significantly reduce the frequency of arch_get_random_seed_long() calls,
>> not sure if that is enough the appease the concerns about the
>> potentially long latency of SMC calls. I also dropped the direct
>> arch_get_random() call in KVM for the same reason. An alternative could
>> be to just use the SMC in the _early() versions, but then we would lose
>> the SMCCC entropy source for the periodic reseeds. This could be mitigated
>> by using a hwrng driver [2] and rngd.
>> The only other non-minor change to v2 is the addition of using the SMCCC
>> call in the _early() variant. For a changelog see below.
>>
>> Sudeep: patch 1/5 is a prerequisite for all other patches, which
>> themselves could be considered separate and need to go via different trees.
>> If we could agree on that one now and get that merged, it would help the
>> handling of the other patches going forward.
>>
>> Cheers,
>> Andre
>> ==============================
>>
>> The ARM architected TRNG firmware interface, described in ARM spec
>> DEN0098[3], defines an ARM SMCCC based interface to a true random number
>> generator, provided by firmware.
>>
>> This series collects all the patches implementing this in various
>> places: as a user feeding into the ARCH_RANDOM pool, both for ARM and
>> arm64, and as a service provider for KVM guests.
>>
>> Patch 1 introduces the interface definition used by all three entities.
>> Patch 2 prepares the Arm SMCCC firmware driver to probe for the
>> interface. This patch is needed to avoid a later dependency on *two*
>> patches (there might be a better solution to this problem).
>>
>> Patch 3 implements the ARM part, patch 4 is the arm64 version.
>> The final patch 5 adds support to provide random numbers to KVM guests.
>>
>> This was tested on:
>> - QEMU -kernel (no SMCCC, regression test)
>> - Juno w/ prototype of the h/w Trusted RNG support
>> - mainline KVM (SMCCC, but no TRNG: regression test)
>> - ARM and arm64 KVM guests, using the KVM service in patch 5/5
>>
>> Based on v5.10-rc3, please let me know if I should rebased on something
>> else. A git repo is accessible at:
>> https://gitlab.arm.com/linux-arm/linux-ap/-/commits/smccc-trng/v3/
>>
>> Cheers,
>> Andre
>>
>> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2020-November/615446.html
>> [2] https://gitlab.arm.com/linux-arm/linux-ap/-/commit/87e3722f437
>> [3] https://developer.arm.com/documentation/den0098/latest/
>>
>> Changelog v2 ... v3:
>> - ARM: fix compilation with randconfig
>> - arm64: use SMCCC call also in arch_get_random_seed_long_early()
>> - KVM: comment on return value usage
>> - KVM: use more interesting UUID (enjoy, Marc!)
> 
> UUIDs are constructed using certain rules, so probably better to
> refrain from playing games with them here.

Hey, it's a valid variant 1 version 1 UUID (otherwise this would be no
real easter egg). uuidgen -t should be able to generate this one. I
found it too easy to use the random variant, but we can revert to that.

> If Marc wants an easter egg, he will have to wait until Easter.

Don't mess with your maintainer ;-)

Cheers,
Andre

> 
>> - KVM: use bitmaps instead of open coded long arrays
>> - KVM: drop direct usage of arch_get_random() interface
>>
>> Changelog "v1" ... v2:
>> - trigger ARCH_RANDOM initialisation from the SMCCC firmware driver
>> - use a single bool in smccc.c to hold the initialisation state for arm64
>> - handle endianess correctly in the KVM provider
>>
>> Andre Przywara (2):
>>   firmware: smccc: Introduce SMCCC TRNG framework
>>   arm64: Add support for SMCCC TRNG entropy source
>>
>> Ard Biesheuvel (3):
>>   firmware: smccc: Add SMCCC TRNG function call IDs
>>   ARM: implement support for SMCCC TRNG entropy source
>>   KVM: arm64: implement the TRNG hypervisor call
>>
>>  arch/arm/Kconfig                    |  4 ++
>>  arch/arm/include/asm/archrandom.h   | 74 +++++++++++++++++++++++++
>>  arch/arm64/include/asm/archrandom.h | 79 +++++++++++++++++++++++----
>>  arch/arm64/include/asm/kvm_host.h   |  2 +
>>  arch/arm64/kvm/Makefile             |  2 +-
>>  arch/arm64/kvm/hypercalls.c         |  6 ++
>>  arch/arm64/kvm/trng.c               | 85 +++++++++++++++++++++++++++++
>>  drivers/firmware/smccc/smccc.c      |  5 ++
>>  include/linux/arm-smccc.h           | 31 +++++++++++
>>  9 files changed, 277 insertions(+), 11 deletions(-)
>>  create mode 100644 arch/arm/include/asm/archrandom.h
>>  create mode 100644 arch/arm64/kvm/trng.c
>>
>> --
>> 2.17.1
>>