19. Realm Management Extension (RME)

FEAT_RME (or RME for short) is an Armv9-A extension and is one component of the Arm Confidential Compute Architecture (Arm CCA). TF-A supports RME starting from version 2.6. This chapter discusses the changes to TF-A to support RME and provides instructions on how to build and run TF-A with RME.

19.1. RME support in TF-A

The following diagram shows an Arm CCA software architecture with TF-A as the EL3 firmware. In the Arm CCA architecture there are two additional security states and address spaces: Root and Realm. TF-A firmware runs in the Root world. In the realm world, a Realm Management Monitor firmware (RMM) manages the execution of Realm VMs and their interaction with the hypervisor.

../_images/arm-cca-software-arch.png

RME is the hardware extension to support Arm CCA. To support RME, various changes have been introduced to TF-A. We discuss those changes below.

19.1.1. Changes to translation tables library

RME adds Root and Realm Physical address spaces. To support this, two new memory type macros, MT_ROOT and MT_REALM, have been added to the Translation (XLAT) Tables Library. These macros are used to configure memory regions as Root or Realm respectively.

Note

Only version 2 of the translation tables library supports the new memory types.

19.1.2. Changes to context management

A new CPU context for the Realm world has been added. The existing CPU context management API can be used to manage Realm context.

19.1.3. Boot flow changes

In a typical TF-A boot flow, BL2 runs at Secure-EL1. However when RME is enabled, TF-A runs in the Root world at EL3. Therefore, the boot flow is modified to run BL2 at EL3 when RME is enabled. In addition to this, a Realm-world firmware (RMM) is loaded by BL2 in the Realm physical address space.

The boot flow when RME is enabled looks like the following:

  1. BL1 loads and executes BL2 at EL3

  2. BL2 loads images including RMM

  3. BL2 transfers control to BL31

  4. BL31 initializes SPM (if SPM is enabled)

  5. BL31 initializes RMM

  6. BL31 transfers control to Normal-world software

19.1.4. Granule Protection Tables (GPT) library

Isolation between the four physical address spaces is enforced by a process called Granule Protection Check (GPC) performed by the MMU downstream any address translation. GPC makes use of Granule Protection Table (GPT) in the Root world that describes the physical address space assignment of every page (granule). A GPT library that provides APIs to initialize GPTs and to transition granules between different physical address spaces has been added. More information about the GPT library can be found in the Granule Protection Tables Library chapter.

19.1.5. RMM Dispatcher (RMMD)

RMMD is a new standard runtime service that handles the switch to the Realm world. It initializes the RMM and handles Realm Management Interface (RMI) SMC calls from Non-secure and Realm worlds.

19.1.6. Test Realm Payload (TRP)

TRP is a small test payload that runs at R-EL2 and implements a subset of the Realm Management Interface (RMI) commands to primarily test EL3 firmware and the interface between R-EL2 and EL3. When building TF-A with RME enabled, if a path to an RMM image is not provided, TF-A builds the TRP by default and uses it as RMM image.

19.2. Building and running TF-A with RME

This section describes how you can build and run TF-A with RME enabled. We assume you have all the Prerequisites to build TF-A.

To enable RME, you need to set the ENABLE_RME build flag when building TF-A. Currently, this feature is only supported for the FVP platform.

The following instructions show you how to build and run TF-A with RME for two scenarios: TF-A with TF-A Tests, and four-world execution with Hafnium and TF-A Tests. The instructions assume you have already obtained TF-A. You can use the following command to clone TF-A.

git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git

To run the tests, you need an FVP model. Please use the latest version of FVP_Base_RevC-2xAEMvA model.

Note

ENABLE_RME build option is currently experimental.

19.2.1. Building TF-A with TF-A Tests

Use the following instructions to build TF-A with TF-A Tests as the non-secure payload (BL33).

1. Obtain and build TF-A Tests

git clone https://git.trustedfirmware.org/TF-A/tf-a-tests.git
cd tf-a-tests
make CROSS_COMPILE=aarch64-none-elf- PLAT=fvp DEBUG=1

This produces a TF-A Tests binary (tftf.bin) in the build/fvp/debug directory.

2. Build TF-A

cd trusted-firmware-a
make CROSS_COMPILE=aarch64-none-elf- \
PLAT=fvp \
ENABLE_RME=1 \
FVP_HW_CONFIG_DTS=fdts/fvp-base-gicv3-psci-1t.dts \
DEBUG=1 \
BL33=<path/to/tftf.bin> \
all fip

This produces bl1.bin and fip.bin binaries in the build/fvp/debug directory. The above command also builds TRP. The TRP binary is packaged in fip.bin.

19.2.2. Four-world execution with Hafnium and TF-A Tests

Four-world execution involves software components at each security state: root, secure, realm and non-secure. This section describes how to build TF-A with four-world support. We use TF-A as the root firmware, Hafnium as the secure component, TRP as the realm-world firmware and TF-A Tests as the non-secure payload.

Before building TF-A, you first need to build the other software components. You can find instructions on how to get and build TF-A Tests above.

1. Obtain and build Hafnium

git clone --recurse-submodules https://git.trustedfirmware.org/hafnium/hafnium.git
cd hafnium
#  Use the default prebuilt LLVM/clang toolchain
PATH=$PWD/prebuilts/linux-x64/clang/bin:$PWD/prebuilts/linux-x64/dtc:$PATH
make PROJECT=reference

The Hafnium binary should be located at out/reference/secure_aem_v8a_fvp_clang/hafnium.bin

2. Build TF-A

Build TF-A with RME as well as SPM enabled.

make CROSS_COMPILE=aarch64-none-elf- \
PLAT=fvp \
ENABLE_RME=1 \
FVP_HW_CONFIG_DTS=fdts/fvp-base-gicv3-psci-1t.dts \
SPD=spmd \
SPMD_SPM_AT_SEL2=1 \
BRANCH_PROTECTION=1 \
CTX_INCLUDE_PAUTH_REGS=1 \
DEBUG=1 \
SP_LAYOUT_FILE=<path/to/tf-a-tests>/build/fvp/debug/sp_layout.json> \
BL32=<path/to/hafnium.bin> \
BL33=<path/to/tftf.bin> \
all fip

19.2.3. Running the tests

Use the following command to run the tests on FVP. TF-A Tests should boot and run the default tests including RME tests.

FVP_Base_RevC-2xAEMvA \
-C bp.flashloader0.fname=<path/to/fip.bin> \
-C bp.secureflashloader.fname=<path/to/bl1.bin> \
-C bp.refcounter.non_arch_start_at_default=1 \
-C bp.refcounter.use_real_time=0 \
-C bp.ve_sysregs.exit_on_shutdown=1 \
-C cache_state_modelled=1 \
-C cluster0.NUM_CORES=4 \
-C cluster0.PA_SIZE=48 \
-C cluster0.ecv_support_level=2 \
-C cluster0.gicv3.cpuintf-mmap-access-level=2 \
-C cluster0.gicv3.without-DS-support=1 \
-C cluster0.gicv4.mask-virtual-interrupt=1 \
-C cluster0.has_arm_v8-6=1 \
-C cluster0.has_branch_target_exception=1 \
-C cluster0.has_rme=1 \
-C cluster0.has_rndr=1 \
-C cluster0.has_amu=1 \
-C cluster0.has_v8_7_pmu_extension=2 \
-C cluster0.max_32bit_el=-1 \
-C cluster0.restriction_on_speculative_execution=2 \
-C cluster0.restriction_on_speculative_execution_aarch32=2 \
-C cluster1.NUM_CORES=4 \
-C cluster1.PA_SIZE=48 \
-C cluster1.ecv_support_level=2 \
-C cluster1.gicv3.cpuintf-mmap-access-level=2 \
-C cluster1.gicv3.without-DS-support=1 \
-C cluster1.gicv4.mask-virtual-interrupt=1 \
-C cluster1.has_arm_v8-6=1 \
-C cluster1.has_branch_target_exception=1 \
-C cluster1.has_rme=1 \
-C cluster1.has_rndr=1 \
-C cluster1.has_amu=1 \
-C cluster1.has_v8_7_pmu_extension=2 \
-C cluster1.max_32bit_el=-1 \
-C cluster1.restriction_on_speculative_execution=2 \
-C cluster1.restriction_on_speculative_execution_aarch32=2 \
-C pci.pci_smmuv3.mmu.SMMU_AIDR=2 \
-C pci.pci_smmuv3.mmu.SMMU_IDR0=0x0046123B \
-C pci.pci_smmuv3.mmu.SMMU_IDR1=0x00600002 \
-C pci.pci_smmuv3.mmu.SMMU_IDR3=0x1714 \
-C pci.pci_smmuv3.mmu.SMMU_IDR5=0xFFFF0475 \
-C pci.pci_smmuv3.mmu.SMMU_S_IDR1=0xA0000002 \
-C pci.pci_smmuv3.mmu.SMMU_S_IDR2=0 \
-C pci.pci_smmuv3.mmu.SMMU_S_IDR3=0 \
-C bp.pl011_uart0.out_file=uart0.log \
-C bp.pl011_uart1.out_file=uart1.log \
-C bp.pl011_uart2.out_file=uart2.log \
-C pctl.startup=0.0.0.0 \
-Q 1000 \
"$@"

The bottom of the output from uart0 should look something like the following.

...

> Test suite 'FF-A Interrupt'
                                                               Passed
> Test suite 'SMMUv3 tests'
                                                               Passed
> Test suite 'PMU Leakage'
                                                               Passed
> Test suite 'DebugFS'
                                                               Passed
> Test suite 'Realm payload tests'
                                                               Passed
> Test suite 'Invalid memory access'
                                                               Passed
...