Re: [RFC] Support for Arm CCA VMs on Linux

Suzuki K Poulose
2023-03-01T09:59:37Z

Hi Dave

Thanks for your response, and apologies for the delay. Response, in line.

On 14/02/2023 17:13, Dr. David Alan Gilbert wrote:
> * Suzuki K Poulose (suzuki.poulose@arm.com) wrote:
>> We are happy to announce the early RFC version of the Arm
>> Confidential Compute Architecture (CCA) support for the Linux
>> stack. The intention is to seek early feedback in the following areas:
>> * KVM integration of the Arm CCA
>> * KVM UABI for managing the Realms, seeking to generalise the operations
>> wherever possible with other Confidential Compute solutions.
>> Note: This version doesn't support Guest Private memory, which will be added
>> later (see below).
>> * Linux Guest support for Realms
>>
>> Arm CCA Introduction
>> =====================
>>
>> The Arm CCA is a reference software architecture and implementation that builds
>> on the Realm Management Extension (RME), enabling the execution of Virtual
>> machines, while preventing access by more privileged software, such as hypervisor.
>> The Arm CCA allows the hypervisor to control the VM, but removes the right for
>> access to the code, register state or data that is used by VM.
>> More information on the architecture is available here[0].
>>
>> Arm CCA Reference Software Architecture
>>
>> Realm World || Normal World || Secure World ||
>> || | || ||
>> EL0 x-------x || x----x | x------x || ||
>> | Realm | || | | | | | || ||
>> | | || | VM | | | | || ||
>> ----| VM* |---------||-| |---| |-||----------------||
>> | | || | | | | H | || ||
>> EL1 x-------x || x----x | | | || ||
>> ^ || | | o | || ||
>> | || | | | || ||
>> ------- R*------------------------| s -|---------------------
>> S || | | || ||
>> I || | t | || ||
>> | || | | || ||
>> v || x------x || ||
>> EL2 RMM* || ^ || ||
>> ^ || | || ||
>> ========|=============================|========================
>> | | SMC
>> x--------- *RMI* -------------x
>>
>> EL3 Root World
>> EL3 Firmware
>> ===============================================================
>> Where :
>> RMM - Realm Management Monitor
>> RMI - Realm Management Interface
>> RSI - Realm Service Interface
>> SMC - Secure Monitor Call
>
> Hi,
> It's nice to see this full stack posted - thanks!
>
> Are there any pointers to information on attestation and similar
> measurement things? In particular, are there any plans for a vTPM

The RMM v1.0 provides attestation and measurement services to the Realm,
via Realm Service Interface (RSI) calls. However, there is no support
for partitioning the Realm VM with v1.0. This is currently under
development and should be available in the near future.

With that in place, a vTPM could reside in a partition of the Realm VM
along side the OS in another. Does that answer your question ?

Kind regards
Suzuki

> for Realms - if there were, it would make life easy for us, since we
> can share some user space stuff with other CoCo systems.
>
> Dave
>
>> RME introduces a new security state "Realm world", in addition to the
>> traditional Secure and Non-Secure states. The Arm CCA defines a new component,
>> Realm Management Monitor (RMM) that runs at R-EL2. This is a standard piece of
>> firmware, verified, installed and loaded by the EL3 firmware (e.g, TF-A), at
>> system boot.
>>
>> The RMM provides standard interfaces - Realm Management Interface (RMI) - to the
>> Normal world hypervisor to manage the VMs running in the Realm world (also called
>> Realms in short). These are exposed via SMC and are routed through the EL3
>> firmwre.
>> The RMI interface includes:
>> - Move a physical page from the Normal world to the Realm world
>> - Creating a Realm with requested parameters, tracked via Realm Descriptor (RD)
>> - Creating VCPUs aka Realm Execution Context (REC), with initial register state.
>> - Create stage2 translation table at any level.
>> - Load initial images into Realm Memory from normal world memory
>> - Schedule RECs (vCPUs) and handle exits
>> - Inject virtual interrupts into the Realm
>> - Service stage2 runtime faults with pages (provided by host, scrubbed by RMM).
>> - Create "shared" mappings that can be accessed by VMM/Hyp.
>> - Reclaim the memory allocated for the RAM and RTTs (Realm Translation Tables)
>>
>> However v1.0 of RMM specifications doesn't support:
>> - Paging protected memory of a Realm VM. Thus the pages backing the protected
>> memory region must be pinned.
>> - Live migration of Realms.
>> - Trusted Device assignment.
>> - Physical interrupt backed Virtual interrupts for Realms
>>
>> RMM also provides certain services to the Realms via SMC, called Realm Service
>> Interface (RSI). These include:
>> - Realm Guest Configuration.
>> - Attestation & Measurement services
>> - Managing the state of an Intermediate Physical Address (IPA aka GPA) page.
>> - Host Call service (Communication with the Normal world Hypervisor)
>>
>> The specifications for the RMM software is currently at *v1.0-Beta2* and the
>> latest version is available here [1].
>>
>> The Trusted Firmware foundation has an implementation of the RMM - TF-RMM -
>> available here [3].
>>
>> Implementation
>> =================
>>
>> This version of the stack is based on the RMM specification v1.0-Beta0[2], with
>> following exceptions :
>> - TF-RMM/KVM currently doesn't support the optional features of PMU,
>> SVE and Self-hosted debug (coming soon).
>> - The RSI_HOST_CALL structure alignment requirement is reduced to match
>> RMM v1.0 Beta1
>> - RMI/RSI version numbers do not match the RMM spec. This will be
>> resolved once the spec/implementation is complete, across TF-RMM+Linux stack.
>>
>> We plan to update the stack to support the latest version of the RMMv1.0 spec
>> in the coming revisions.
>>
>> This release includes the following components :
>>
>> a) Linux Kernel
>> i) Host / KVM support - Support for driving the Realms via RMI. This is
>> dependent on running in the Kernel at EL2 (aka VHE mode). Also provides
>> UABI for VMMs to manage the Realm VMs. The support is restricted to 4K page
>> size, matching the Stage2 granule supported by RMM. The VMM is responsible
>> for making sure the guest memory is locked.
>>
>> TODO: Guest Private memory[10] integration - We have been following the
>> series and support will be added once it is merged upstream.
>>
>> ii) Guest support - Support for a Linux Kernel to run in the Realm VM at
>> Realm-EL1, using RSI services. This includes virtio support (virtio-v1.0
>> only). All I/O are treated as non-secure/shared.
>>
>> c) kvmtool - VMM changes required to manage Realm VMs. No guest private memory
>> as mentioned above.
>> d) kvm-unit-tests - Support for running in Realms along with additional tests
>> for RSI ABI.
>>
>> Running the stack
>> ====================
>>
>> To run/test the stack, you would need the following components :
>>
>> 1) FVP Base AEM RevC model with FEAT_RME support [4]
>> 2) TF-A firmware for EL3 [5]
>> 3) TF-A RMM for R-EL2 [3]
>> 4) Linux Kernel [6]
>> 5) kvmtool [7]
>> 6) kvm-unit-tests [8]
>>
>> Instructions for building the firmware components and running the model are
>> available here [9]. Once, the host kernel is booted, a Realm can be launched by
>> invoking the `lkvm` commad as follows:
>>
>> $ lkvm run --realm \
>> --measurement-algo=["sha256", "sha512"] \
>> --disable-sve \
>> <normal-vm-options>
>>
>> Where:
>> * --measurement-algo (Optional) specifies the algorithm selected for creating the
>> initial measurements by the RMM for this Realm (defaults to sha256).
>> * GICv3 is mandatory for the Realms.
>> * SVE is not yet supported in the TF-RMM, and thus must be disabled using
>> --disable-sve
>>
>> You may also run the kvm-unit-tests inside the Realm world, using the similar
>> options as above.
>>
>>
>> Links
>> ============
>>
>> [0] Arm CCA Landing page (See Key Resources section for various documentations)
>> https://www.arm.com/architecture/security-features/arm-confidential-compute-architecture
>>
>> [1] RMM Specification Latest
>> https://developer.arm.com/documentation/den0137/latest
>>
>> [2] RMM v1.0-Beta0 specification
>> https://developer.arm.com/documentation/den0137/1-0bet0/
>>
>> [3] Trusted Firmware RMM - TF-RMM
>> https://www.trustedfirmware.org/projects/tf-rmm/
>> GIT: https://git.trustedfirmware.org/TF-RMM/tf-rmm.git
>>
>> [4] FVP Base RevC AEM Model (available on x86_64 / Arm64 Linux)
>> https://developer.arm.com/Tools%20and%20Software/Fixed%20Virtual%20Platforms
>>
>> [5] Trusted Firmware for A class
>> https://www.trustedfirmware.org/projects/tf-a/
>>
>> [6] Linux kernel support for Arm-CCA
>> https://gitlab.arm.com/linux-arm/linux-cca
>> Host Support branch: cca-host/rfc-v1
>> Guest Support branch: cca-guest/rfc-v1
>>
>> [7] kvmtool support for Arm CCA
>> https://gitlab.arm.com/linux-arm/kvmtool-cca cca/rfc-v1
>>
>> [8] kvm-unit-tests support for Arm CCA
>> https://gitlab.arm.com/linux-arm/kvm-unit-tests-cca cca/rfc-v1
>>
>> [9] Instructions for Building Firmware components and running the model, see
>> section 4.19.2 "Building and running TF-A with RME"
>> https://trustedfirmware-a.readthedocs.io/en/latest/components/realm-management-extension.html#building-and-running-tf-a-with-rme
>>
>> [10] fd based Guest Private memory for KVM
>> https://lkml.kernel.org/r/20221202061347.1070246-1-chao.p.peng@linux.intel.com
>>
>> Cc: Alexandru Elisei <alexandru.elisei@arm.com>
>> Cc: Andrew Jones <andrew.jones@linux.dev>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Chao Peng <chao.p.peng@linux.intel.com>
>> Cc: Christoffer Dall <christoffer.dall@arm.com>
>> Cc: Fuad Tabba <tabba@google.com>
>> Cc: James Morse <james.morse@arm.com>
>> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
>> Cc: Joey Gouly <Joey.Gouly@arm.com>
>> Cc: Marc Zyngier <maz@kernel.org>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Oliver Upton <oliver.upton@linux.dev>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Quentin Perret <qperret@google.com>
>> Cc: Sean Christopherson <seanjc@google.com>
>> Cc: Steven Price <steven.price@arm.com>
>> Cc: Thomas Huth <thuth@redhat.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Zenghui Yu <yuzenghui@huawei.com>
>> To: linux-coco@lists.linux.dev
>> To: kvmarm@lists.linux.dev
>> Cc: kvmarm@lists.cs.columbia.edu
>> Cc: linux-arm-kernel@lists.infradead.org
>> To: linux-kernel@vger.kernel.org
>> To: kvm@vger.kernel.org
>>