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Building an RME stack for QEMU

Building an RME stack for QEMU

Owned by Alex Bennée
Last updated: May 13, 2025 by Jean-Philippe Brucker

The whole software stack for CCA is in development, meaning instructions will change frequently and repositories are temporary. Instructions to compile the stack, both manually and from the OP-TEE build environment, have been written from a Ubuntu 22.04 LTS based system.

Note: Even though this software stack uses OP-TEE build environment, it is not building and running OP-TEE itself.

Release Notes

  1. The latest build is “cca/v8”

  2. Since “cca/v7”, QEMU-virt went back to its original memory support of 3GB. QEMU-sbsa supports larger amounts of memory.

  3. The name of the branch matches the Linux kernel mailing list’s CCA patchset the reference stack is built upon. Individual projects listed in the manifest may or may not have the same naming convention, or may reference older patchsets. This is normal and expected.

  4. There is a lot of churn in the CCA reference stack. As such we encourage users to upgrade to the newest revision when available.

With the OP-TEE build environment

This method requires at least the following tools and libraries. The manual build described below also requires most of them.

  • repo

  • python3-pyelftools, python3-venv

  • acpica-tools

  • openssl (debian libssl-dev)

  • libglib2.0-dev, libpixman-1-dev

  • dtc (debian device-tree-compiler)

  • flex, bison

  • make, cmake, ninja (debian ninja-build), curl, rsync

The easiest way to build and run a complete stack is through OP-TEE. We support two system emulation QEMU machines, i.e Virt and SBSA. The amount of system RAM supported by QEMU-virt is set to at most 8GB and can not be increased. QEMU-sbsa also uses 8GB by default but can be configured between 2GB and 1TB.

The following commands will download all components and build them, in about thirty minutes on a fast machine. To avoid dealing with dependencies you can also build the latest stack in a container environment and run it in a tmux session with this set of scripts.

Virt machine:

mkdir cca cd cca repo init -u https://git.codelinaro.org/linaro/dcap/op-tee-4.2.0/manifest.git -b cca/v8 -m qemu_v8_cca.xml repo sync -j8 --no-clone-bundle cd build make -j8 toolchains make -j8

SBSA machine:

mkdir cca cd cca repo init -u https://git.codelinaro.org/linaro/dcap/op-tee-4.2.0/manifest.git -b cca/v8 -m sbsa_cca.xml repo sync -j8 --no-clone-bundle cd build make -j8 toolchains make -j8

Note:

  • If the build fails, try without -j. It will point out missing dependencies.

  • Add CLOUDHV=y to build cloud-hypervisor. This requires a rust toolchain >= 1.77.

Images can be found under cca/out/ and cca/out-br/. The following command launches system emulation QEMU with the RME feature enabled, running TF-A, RMM and the Linux host.

make run-only

This should launch 4 new terminals, i.e Firmware, Host, Secure and Realm. Output from the boot process will start flowing in the Firmware terminal followed by the Host terminal. The build environment automatically makes the cca directory available to the host VM via 9p.

Read on for the details of the software stack, or skip to the following section to boot a Realm guest.

Manual build

The following sections detail how to build and run all components of the CCA software stack. Two QEMU binaries are built. The system emulation QEMU implements a complete machine, emulating Armv9 CPUs with FEAT_RME and four security states: Root, Secure, Non-secure and Realm. The VMM (Virtual Machine Manager) QEMU is cross-built by buildroot, and launches the realm guest from Non-secure EL0.

| REALM | NON-SECURE | -------+--------------+--------------+ EL0 | Guest Rootfs | Host Rootfs | | | QEMU VMM | -------+--------------+--------------+ EL1 | EDK2 | | | Linux Guest | | | | EDK2 | -------+--------------+ Linux Host | EL2 | TF-RMM | (KVM) | | | | -------+--------------+--------------+ (ROOT)| | EL3 | TF-A | -------+-----------------------------+ HW | QEMU | -------+-----------------------------+

Instructions to build the TF-RMM, TF-A and host EDK2 differ based on the QEMU machine selected for system emulation. All other components of the stack are common to both machines.

Manual build instructions for TF-RMM, TF-A and host EDK2 on QEMU-virt

Manual build instructions for TF-RMM, TF-A and host EDK2 on QEMU-sbsa

Host and guest Linux

Both host and guest need extra patches.

Status: Guest support is in Linux v6.13. Host support on the list

Repo: https://gitlab.arm.com/linux-arm/linux-cca cca-host/v8

Build:

make CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 defconfig # Enable the configfs-tsm driver that provides the attestation interface scripts/config -e VIRT_DRIVERS -e ARM_CCA_GUEST -e CONFIG_HZ_100 \ -d CONFIG_HZ_250 -e CONFIG_MACVLAN -e CONFIG_MACVTAP make CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 -j8 Image

If your configuration is different from arm64 defconfig, do make sure you have CONFIG_RODATA_FULL_DEFAULT_ENABLED=y or pass rodata=full on the kernel command-line. This is to ensure that the direct mapping uses page granularity and can be modified when sharing pages with the guest (see this discussion).

Guest edk2

The QEMU VMM can either launch the guest kernel itself, or launch edk2 which launches the kernel or an intermediate bootloader. That latter method is generally used to boot a Linux distribution. Edk2 needs modifications in order to run as a Realm guest.

Status: in development. Only the ArmVirtQemu firwmare supports booting in a Realm at the moment, not ArmVirtQemuKernel.

Repo: https://git.codelinaro.org/linaro/dcap/edk2 branch cca/latest

Build:

git submodule update --init --recursive source edksetup.sh make -j -C BaseTools export GCC5_AARCH64_PREFIX=aarch64-linux-gnu- build -b RELEASE -a AARCH64 -t GCC5 -p ArmVirtPkg/ArmVirtQemu.dsc

Note that the RELEASE build is a lot faster than the DEBUG build, but doesn’t provide a lot of information. If the boot doesn’t work, try building with -b DEBUG.

Direct kernel boot may fail while the EFI stub loads the initrd from edk2, because the memory is already fragmented at that point and edk2 may not find a contiguous region large enough to transfer the initrd to the kernel. If initrd loading fails, try increasing guest memory.

QEMU and kvmtool VMM

Both kvmtool and QEMU can be used to launch Realm guests.

Status: in development

Repo: https://git.codelinaro.org/linaro/dcap/qemu branch cca/latest
https://git.codelinaro.org/linaro/dcap/kvmtool branch cca/log

Build:

The buildroot recipe below already includes kvmtool and QEMU for CCA, so there is no need to download them separately. For development you can use your own source directory: add a local.mk file at the root of the buildroot build directory, containing:

QEMU_CCA_OVERRIDE_SRCDIR = path/to/qemu KVMTOOL_CCA_OVERRIDE_SRCDIR = path/to/kvmtool

You will need to run make qemu-cca-rebuild in the buildroot build directory after making changes to the QEMU source.

Cloud-hypervisor

Status: in development.

Repo: GitHub - jpbrucker/cloud-hypervisor at cca/latest

Build:

# Install the aarch64 target if necessary rustup target add aarch64-unknown-linux-gnu export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER=aarch64-linux-gnu-gcc cargo build --target=aarch64-unknown-linux-gnu --features=arm_rme

Then copy target/aarch64-unknown-linux-gnu/debug/cloud-hypervisor into the Root filesystem or the shared folder.

Root filesystem

Buildroot provides a convenient way to build lightweight root filesystems.

Repo:

Build:

git clone https://git.codelinaro.org/linaro/dcap/buildroot-external-cca.git git clone https://gitlab.com/buildroot.org/buildroot.git cd buildroot make BR2_EXTERNAL=path/to/buildroot-external-cca/ cca_defconfig make -j16 cp output/images/rootfs.ext4 ../images/ cp output/images/rootfs.cpio ../images/

This creates the rootfs images in buildroot’s output/images/ when building in-tree, or images/ when building out of tree.

Guest disk image for edk2

To create a guest disk image that resembles more a Linux distribution, containing the grub2 bootloader and the kernel, have a look at buildroot’s configs/aarch64_efi_defconfig, which enables a few options to generate a disk with an EFI partition:

BR2_PACKAGE_HOST_GENIMAGE=y BR2_PACKAGE_HOST_DOSFSTOOLS=y BR2_PACKAGE_HOST_MTOOLS=y BR2_TARGET_GRUB2=y BR2_TARGET_GRUB2_ARM64_EFI=y BR2_ROOTFS_POST_IMAGE_SCRIPT="board/aarch64-efi/post-image.sh support/scripts/genimage.sh" BR2_ROOTFS_POST_SCRIPT_ARGS="-c board/aarch64-efi/genimage-efi.cfg" # Copy the guest kernel Image into buildroot's build directory, where it will be # picked up by genimage. mkdir buildroot/output/images/ cp linux/arch/arm64/boot/Image buildroot/output/images/Image make aarch64_efi_defconfig make

With these, after generating the root filesystem, buildroot packs it into another disk image under output/images/disk.imgalong with an EFI FAT partition that contains grub and the kernel Image (layout is defined by board/aarch64-efi/genimage-efi.cfg). File output/images/disk.img should be copied to a location accessible by the RME enabled base system. See variable RUN_DISK in file /usr/share/cca-realm-measurements/gen-run-vmm.cfg on the base root filesystem.

Build the Ubuntu Rootfs

Below there is a scripts to automatically build the ubuntu 22.04 rootfs, it consists of several parts:

  • Generate a 4G image, make partitions and mount.

  • Download the ubuntu-base filesystem and abstract the files to the image

  • Configure the essential files for ubuntu for installing packages.

  • Set up the init process for Ubuntu Rootfs boot.

  • Install essential packages via Chroot, in case of failing enabling the /dev/hvc0 when realm boot.

  • Umount

NOTE: Please copy this content below to a ubuntu_fs.sh and run it with sudo, as the mount, chroot needs the root permissions.

sudo ./ubuntu_fs.sh ubuntu22.img

The above command will generate a ubuntu 22 rootfs with the name ubuntu22.img. It is very easy to launch, just change the disk image to ubuntu22.img and you can enjoy. It can be either running as the Realm Host, or the Realm itself for daily development. Just tweak the scripts below to suit your user cases.

#!/bin/bash img_name="$1" directory="ubuntu_fs" realm_user="realm" realm_password="realm" if [[ $EUID -ne 0 ]]; then echo "Need to run with sudo" exit 1 fi # Check if the img file name parameter is provided if [ -z "$img_name" ]; then echo "Please provide the generated img file name as the first parameter!" exit 1 fi #Generate a 4GB img file echo "Generating 4GB img file $img_name ..." dd if=/dev/zero of="$img_name" bs=1G count=4 || exit 1 # Format the img file as ext4 file system echo "Formatting the img file as ext4 file system..." mkfs.ext4 -F "$img_name" || exit 1 # Check if the directory exists if [ -d "$directory" ]; then echo "Directory $directory exists. Deleting its contents..." rm -rf "$directory"/* else echo "Directory $directory does not exist. Creating the directory..." mkdir "$directory" fi # Mount the img file to the ubuntu_fs directory echo "Mounting the img file to directory $directory..." mount -o loop "$img_name" "$directory" || exit 1 # Download the file echo "Downloading file $archive_file ..." archive_url="https://cdimage.ubuntu.com/ubuntu-base/releases/22.04.4/release/ubuntu-base-22.04.4-base-arm64.tar.gz" archive_file="ubuntu-base-22.04.4-base-arm64.tar.gz" wget "$archive_url" -P "$directory" # Extract the file echo "Extracting file $archive_file to directory $directory..." tar -xf "$directory/$archive_file" -C "$directory" # Remove the downloaded archive file echo "Removing downloaded archive file $archive_file ..." rm "$directory/$archive_file" # Write nameserver to resolv.conf file echo "Writing nameserver to $directory/etc/resolv.conf file..." echo "nameserver 8.8.8.8" > "$directory/etc/resolv.conf" cat > "$directory/etc/apt/sources.list" << EOF deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy main restricted deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy-updates main restricted deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy universe deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy-updates universe deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy multiverse deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy-updates multiverse deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy-backports main restricted universe multiverse deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy-security main restricted deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy-security universe deb http://nova.clouds.ports.ubuntu.com/ubuntu-ports/ jammy-security multiverse EOF # Switch to chroot environment and execute apt command echo "Switching to chroot environment and executing apt command..." mount -t proc /proc $directory/proc mount -t sysfs /sys $directory/sys mount -o bind /dev $directory/dev mount -o bind /dev/pts $directory/dev/pts chroot "$directory" /bin/bash -c "apt update -y" || exit 1 # Create a new user with sudo privileges echo "Creating user $realm_user with sudo privileges..." chroot "$directory" /bin/bash -c "useradd -m -s /bin/bash -G sudo $realm_user" || exit 1 # Set the password for the new user echo "Setting password for user $realm_user..." echo "$realm_user:$realm_password" | chroot "$directory" /bin/bash -c "chpasswd" || exit 1 chroot "$directory" /bin/bash -c "chmod 1777 /tmp" || exit 1 echo "Generate the init file" cat > "$directory/init" << EOF #!/bin/sh [ -d /dev ] || mkdir -m 0755 /dev [ -d /root ] || mkdir -m 0700 /root [ -d /sys ] || mkdir /sys [ -d /proc ] || mkdir /proc [ -d /tmp ] || mkdir /tmp mkdir -p /var/lock mount -t sysfs -o nodev,noexec,nosuid sysfs /sys mount -t proc -o nodev,noexec,nosuid proc /proc # Some things don't work properly without /etc/mtab. ln -sf /proc/mounts /etc/mtab grep -q '\<quiet\>' /proc/cmdline || echo "Loading, please wait..." # Note that this only becomes /dev on the real filesystem if udev's scripts # are used; which they will be, but it's worth pointing out if ! mount -t devtmpfs -o mode=0755 udev /dev; then echo "W: devtmpfs not available, falling back to tmpfs for /dev" mount -t tmpfs -o mode=0755 udev /dev [ -e /dev/console ] || mknod -m 0600 /dev/console c 5 1 [ -e /dev/null ] || mknod /dev/null c 1 3 fi mkdir /dev/pts mount -t devpts -o noexec,nosuid,gid=5,mode=0620 devpts /dev/pts || true mount -t tmpfs -o "noexec,nosuid,size=10%,mode=0755" tmpfs /run mkdir /run/initramfs # compatibility symlink for the pre-oneiric locations ln -s /run/initramfs /dev/.initramfs # Set modprobe env export MODPROBE_OPTIONS="-qb" # mdadm needs hostname to be set. This has to be done before the udev rules are called! if [ -f "/etc/hostname" ]; then /bin/hostname -b -F /etc/hostname 2>&1 1>/dev/null fi exec /sbin/init EOF chmod +x $directory/init || exit 1 chroot "$directory" /bin/bash -c "apt install systemd iptables -y" || exit 1 chroot "$directory" /bin/bash -c "ln -s /lib/systemd/systemd /sbin/init" || exit 1 echo "Install other essential components, in case of booting blocking at /dev/hvc0 failed to bring up" chroot "$directory" /bin/bash -c "apt install vim bash-completion net-tools iputils-ping ifupdown ethtool ssh rsync udev htop rsyslog curl openssh-server apt-utils dialog nfs-common psmisc language-pack-en-base sudo kmod apt-transport-https -y" || exit 1 # Unmount the mounted directory echo "Unmounting the mounted directory $directory ..." umount $directory/proc umount $directory/sys umount $directory/dev/pts umount $directory/dev umount "$directory" echo "Operation completed!"

QEMU system emulation

Repo: QEMU / QEMU · GitLab or the same repository as the VMM.

Build: do not build in the same source directory as the VMM! Since buildroot copies the whole content of that source directory, binary files will conflict (the VMM is cross-built while the system emulation QEMU is native).

git clone https://gitlab.com/qemu-project/qemu.git cd qemu ./configure --target-list=aarch64-softmmu --enable-slirp --disable-docs make -j16

If you want to use the same source directory as the target QEMU, QEMU integrated in buildroot, do use a separate build directory as described here:

mkdir -p ../build/qemu/ # outside of the source directory cd ../build/qemu/ ../../qemu/configure --target-list=aarch64-softmmu --enable-slirp --disable-docs make -j16

Running the system emulation

QEMU will connect to four TCP ports for the different consoles. Create the servers manually with socat -,rawer TCP-LISTEN:5432x (x = 0, 1, 2, 3) or use the script given at the end in section “Spawn four consoles with servers listening for QEMU system emulation”:

QEMU-virt startup script:

Note: KASLR must be disabled to workaround a limitation of TF-A for virt platform (see details)

qemu-system-aarch64 -M virt,virtualization=on,secure=on,gic-version=3 -M acpi=off -cpu max,x-rme=on -m 8G -smp 8 -nographic -bios trusted-firmware-a/flash.bin -kernel linux-cca/arch/arm64/boot/Image -drive format=raw,if=none,file=buildroot/output/images/rootfs.ext4,id=hd0 -device virtio-blk-pci,drive=hd0 # The following parameters allow to use separate consoles for Firmware (port 54320), # Secure payload (54321), host (54322) and guest (54323). -nodefaults -serial tcp:localhost:54320 -serial tcp:localhost:54321 -chardev socket,mux=on,id=hvc0,port=54322,host=localhost -device virtio-serial-device -device virtconsole,chardev=hvc0 -chardev socket,mux=on,id=hvc1,port=54323,host=localhost -device virtio-serial-device -device virtconsole,chardev=hvc1 -append "root=/dev/vda console=hvc0 nokaslr" -device virtio-net-pci,netdev=net0 -netdev user,id=net0 # This shares the current directory with the host, providing the files needed # to launch the guest. -device virtio-9p-device,fsdev=shr0,mount_tag=shr0 -fsdev local,security_model=none,path=.,id=shr0

QEMU-sbsa startup script:

qemu-system-aarch64 \ -machine sbsa-ref -m 8G \ -cpu max,x-rme=on,sme=off,pauth-impdef=on \ -drive file=images/SBSA_FLASH0.fd,format=raw,if=pflash \ -drive file=images/SBSA_FLASH1.fd,format=raw,if=pflash \ -drive file=fat:rw:images/disks/virtual,format=raw \ -drive format=raw,if=none,file=buildroot/output/images/rootfs.ext4,id=hd0 \ -device virtio-blk-pci,drive=hd0 \ -serial tcp:localhost:54320 \ -serial tcp:localhost:54321 \ -chardev socket,mux=on,id=hvc0,port=54322,host=localhost \ -device virtio-serial-pci \ -device virtconsole,chardev=hvc0 \ -chardev socket,mux=on,id=hvc1,port=54323,host=localhost \ -device virtio-serial-pci \ -device virtconsole,chardev=hvc1 \ -device virtio-9p-pci,fsdev=shr0,mount_tag=shr0 \ -fsdev local,security_model=none,path=../../,id=shr0

 

Crucially, the x-rme=on parameter enables the (experimental) FEAT_RME.

In the host kernel log, verify that KVM communicates with the RMM and is ready to launch Realm guests:

[ 0.893261] kvm [1]: Using prototype RMM support (version 66.0)

Note: The virt platform currently has at most 8GB of RAM, which we believe is enough memory to demonstrate how CCA works in a simulated environment. Modifications to the trusted firmware and RMM elements are needed if a different value is selected.

Launching a Realm guest

Once at the host command line prompt simply use root to log in.

Using buildroot-external-cca, the shared directory should be automatically mounted. Otherwise mount it with with:

mount -t 9p shr0 /mnt

Launching a Realm guest using QEMU

When using buildroot-external-cca, the filesystem should contain a script provided by cca-realm-measurements. Launch the VM with:

gen-run-vmm.sh --tap --extcon

Using a tap network puts the guest on the same network as the host, and allows running the attestation demo below.

Or manually (with user networking rather than tap):

qemu-system-aarch64 \ -M confidential-guest-support=rme0 \ -object rme-guest,id=rme0,measurement-algorithm=sha512 \ -nodefaults \ -chardev stdio,mux=on,id=virtiocon0,signal=off \ -device virtio-serial-pci \ -device virtconsole,chardev=virtiocon0 \ -mon chardev=virtiocon0,mode=readline \ -kernel /mnt/out/bin/Image \ -initrd /mnt/out-br/images/rootfs.cpio \ -device virtio-net-pci,netdev=net0,romfile= \ -netdev user,id=net0 \ -cpu host -M virt -enable-kvm -M gic-version=3,its=on \ -smp 2 -m 512M -nographic \ -append console=hvc0 < /dev/hvc1 >/dev/hvc1

The -M confidential-guest-support=rme0 and -object rme-guest,id=rme0 parameters declare this as a Realm VM.

You should see RMM logs in the Firmware terminal:

# RMI (Realm Management Interface) is the protocol that host uses to # communicate with the RMM SMC_RMM_REC_CREATE 45659000 456ad000 446b1000 > RMI_SUCCESS SMC_RMM_REALM_ACTIVATE 45659000 > RMI_SUCCESS # RSI (Realm Service Interface) is the protocol that the guest uses to # communicate with the RMM SMC_RSI_ABI_VERSION > d0000 SMC_RSI_REALM_CONFIG 41afe000 > RSI_SUCCESS SMC_RSI_IPA_STATE_SET 40000000 60000000 1 0 > RSI_SUCCESS 60000000

Followed a few minutes later by the guest kernel starting in the Realm terminal.

Launching a Realm guest using Kvmtool

gen-run-vmm.sh --kvmtool --tap --extcon

or manually:

lkvm run --realm -c 2 -m 2G -k /mnt/out/bin/Image -d /mnt/out-br/images/rootfs.ext4 --restricted_mem -p "console=hvc0 root=/dev/vda" < /dev/hvc1 > /dev/hvc1

Launching a Realm guest using cloud-hypervisor

This example uses a macvtap interface to connect the guest to the host network. CONFIG_MACVTAP needs to be 'y' in the host kernel config.

gen-run-vmm.sh --cloudhv --extcon

or manually:

ip link add link eth0 name macvtap0 type macvtap ip link set macvtap0 up tapindex=$(cat /sys/class/net/macvtap0/ifindex) tapaddress=$(cat /sys/class/net/macvtap0/address) tapdevice="/dev/tap$tapindex" /mnt/out/bin/cloud-hypervisor --platform arm_rme=on --kernel /mnt/out/bin/Image --disk path=/mnt/out-br/images/rootfs.ext4 --cpus boot=2 --memory size=512M --net fd=3,mac=$tapaddress --cmdline "console=hvc0 root=/dev/vda" < /dev/hvc1 > /dev/hvc1 3<>$tapdevice

Running edk2 as a guest

Enable USE_EDK2 to boot the Realm guest with the edk2 firmware. It can either load kernel and initrd through the FwCfg device provided by QEMU, or launch a bootloader from a disk image (gen-run-vmm.sh --edk2 --disk-boot). See section Guest disk image for edk2 for details on how to generate the disk image expected by --disk-boot.

When booting the kernel directly, edk2 measures the kernel, initrd and parameters provided on the QEMU command-line and adds them to the Realm Extended Measurement via RSI calls, so that they can be attested later.

Notes:

  • When booting via grub2, the kernel parameters are stored in grub.cfg which is copied from board/aarch64-efi/grub.cfg by the buildroot script board/aarch64-efi/post-image.sh. By default the kernel parameters do not define a console, so Linux will determine the boot console from the device tree’s /chosen/stdout-path property, which QEMU initializes to the default serial console. So if you want to boot with virtconsole, add console=hvc0 to $(BUILDROOT)board/aarch64-efi/grub.cfg before making buildroot.

Attestation Proof of Concept

Two demonstration applications are available in the root file system.

cca-workload-attestation

From a Realm VM, you can query the RMM for a CCA attestation token that is printed to the console and saved to a file:

cca-workload-attestation report

The tool can also demonstrate a typical interaction with an attestation service by communicating the CCA attestation token to an instance of the Veraison services:

cca-workload-attestation passport

Details on the cca-workload-attestation, the Veraison services and the endorser that populate the endorsement values can be found here.

keybroker-demo

The keybroker demo shows interaction between an attester, a relying party and a verifier. The keybroker-app, running in the Realm, requests a secret key from keybroker-server, run by the relying party.

Repo: GitHub - veraison/keybroker-demo: A simple key broker protocol

Build: the keybroker server

cd rust-keybroker cargo build

Run:

The server, on the build machine, listens on port 8088, and connects to the Linaro veraison instance for platform token verification. You can change these settings with command-line options.

target/debug/keybroker-server -e http://10.0.2.2 -v

The client, in the Realm, requests secret key “skywalker”:

keybroker-app skywalker -e http://10.0.2.2:8088 -v

You will normally get the following error:

INFO Attestation failure :-( ! AttestationFailure: No attestation result was obtained. No known-good reference values.

This means that the platform token verification succeeded, but the realm token verification did not. The Realm Initial Measurement is not known by the server:

INFO Known-good RIM values are missing. If you trust the client that submitted evidence for challenge 2961561008, you should restart the keybroker-server with the following command-line option to populate it with known-good RIM values: --reference-values <(echo '{ "reference-values": [ "WE/l0rYWLJykPTBwM92hM39VFpy9OdqvBHsQpjXfTEzXZGTf+D5n2Fqqhb4Zi/L3TMbYH9opnzjQL2EDa8TXUg==" ] }')

Retrying the key request after restarting the server with the suggested parameter should now succeed:

INFO Attestation success :-) ! The key returned from the keybroker is 'May the force be with you.'

realm-measurements

Instead of running the server twice, you can also predict the Realm Initial Measurement, even before running the guest, using the cca-realm-measurements tool.

Repo: GitHub - veraison/cca-realm-measurements: Tool to compute Realm initial and extended measurements for Arm CCA

Build:

cargo build # Create a local configuration: cat << EOF > gen-run-vmm.cfg REALM_MEASUREMENTS=target/debug/realm-measurements CONFIGS_DIR=configs # The root of the optee build directory BUILD=path/to/cca KERNEL=\$BUILD/out/bin/Image INITRD=\$BUILD/out-br/images/rootfs.cpio EDK2_DIR=\$BUILD/edk2 EOF

Run:

scripts/gen-run-vmm.sh --gen-measurements # outputs: + target/debug/realm-measurements -c configs/qemu-max-8.2.conf -c configs/kvm.conf -k /build/cca/out/bin/Image -i /build/cca/out-br/images/rootfs.cpio -f /Build/ArmVirtQemu-AARCH64/DEBUG_GCC5/FV/QEMU_EFI.fd --print-b64 qemu -M confidential-guest-support=rme0 -object rme-guest,id=rme0,measurement-algorithm=sha512 -nodefaults -chardev stdio,mux=on,id=virtiocon0,signal=off -device virtio-serial-pci -device virtconsole,chardev=virtiocon0 -mon chardev=virtiocon0,mode=readline -kernel /build/cca/out/bin/Image -initrd /build/cca/out-br/images/rootfs.cpio -device virtio-net-pci,netdev=net0,romfile= -netdev user,id=net0 -cpu host -M virt -enable-kvm -M gic-version=3,its=on -smp 2 -m 512M -nographic -dtb qemu-gen.dtb -append console=hvc0 RIM: eZ25AQETulL4kIvgJi/yCVi12ASeD1MOvIwSq9gwNT7HYPAjWePnMcLfH4OaHEafW6V4MnZfgWxgr5uYQnG26Q==

Since this is the same script that you use to launch the VM, it already knows the QEMU command-line arguments that you use, and the generated DTB loaded into the VM. Since you also give it the kernel and initrd images that will be loaded into the Realm, it will correctly predict the resulting Realm Initial Measurement (RIM). You can of course run the realm-measurements tool manually if you use a different VMM command-line.

Pass the resulting RIM to keybroker-server:

target/debug/keybroker-server -e http://10.0.2.2 -v --reference-values <(echo '{ "reference-values": [ "eZ25AQETulL4kIvgJi/yCVi12ASeD1MOvIwSq9gwNT7HYPAjWePnMcLfH4OaHEafW6V4MnZfgWxgr5uYQnG26Q==" ] }')

 

When running your own veraison instance (see the documentation and poc-endorser), you can also provision the verifier with reference values directly, so cca-workload-attestation passport can obtain an affirming appraisal of the realm token:

scripts/gen-run-vmm.sh --corim-output realm-corim.cbor veraison -- cocli corim submit --corim-file realm-corim.cbor --media-type 'application/corim-unsigned+cbor; profile="http://arm.com/cca/realm/1"'

And in the guest:

# veraison.example points to the machine running the veraison instance (build machine) $ cat /etc/hosts 10.0.2.2 veraison.example $ cca-workload-attestation passport { "ear.verifier-id": { "build": "N/A", "developer": "Veraison Project" }, "eat_nonce": "zM2RxZM5agCVJs2EyaWLmtDEM5qq7jj0xcXmLsdi56Bz8SnYSbBwQtpzdHUUMv5WWg5d8zFypap_oz5HzySknQ==", "eat_profile": "tag:github.com,2023:veraison/ear", "iat": 1733322149, "submods": { "CCA_REALM": { "ear.appraisal-policy-id": "policy:ARM_CCA", "ear.status": "affirming", "ear.trustworthiness-vector": { "configuration": 0, "executables": 2, "file-system": 0, "hardware": 0, "instance-identity": 2, "runtime-opaque": 0, "sourced-data": 0, "storage-opaque": 0 }, "ear.veraison.annotated-evidence": { "cca-realm-challenge": "zM2RxZM5agCVJs2EyaWLmtDEM5qq7jj0xcXmLsdi56Bz8SnYSbBwQtpzdHUUMv5WWg5d8zFypap/oz5HzySknQ==", "cca-realm-extensible-measurements": [ "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==", "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==", "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==", "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==" ], "cca-realm-hash-algo-id": "sha-512", "cca-realm-initial-measurement": "pHeSIWwfShg9v8l38mqDGHloBvWCtBg7eJ9/zKG5hnjfQs2ACqZk/+sx1/f1A2h7TuKxoSPNhq4p5vkrKl1lBg==", "cca-realm-personalization-value": "q80AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==", "cca-realm-profile": "tag:arm.com,2023:realm#1.0.0", "cca-realm-public-key": "pAECIAIhWDB2+YgJG+WF7UGAGuz6uFhUjGMFfhaw5nYSC70NL5wp4FbF1BoBMOucIVF4mdwjFGsiWDAo4bBivT6ksxX9IZ8cu1KMtudMpJvhZ3NzT2GhymEDGyu/PZGPL5T/xCKOUJGVRK4=", "cca-realm-public-key-hash-algo-id": "sha-256" } }, "CCA_SSD_PLATFORM": { "ear.appraisal-policy-id": "policy:ARM_CCA", "ear.status": "affirming", ...

Tips

Automate some things in the host boot

You can add files to the buildroot images by providing an overlay directory. The BR2_ROOTFS_OVERLAY option points to the directory that will be added into the image. For example I use:

├── etc │   ├── init.d │   │   └── S50-shr │   └── inittab

S50-shr is an initscript that mounts the shared directory:

#!/bin/sh case $1 in start) mkdir -p /mnt/shr0/ mount -t 9p shr0 /mnt/shr0/ ;; stop) umount /mnt/shr0/ rmdir /mnt/shr0/ ;; esac

inittab is buildroot’s package/busybox/inittab, modified to automatically log into root (the respawn line). It could also mount the 9p filesystem.

# /etc/inittab # # Copyright (C) 2001 Erik Andersen <andersen@codepoet.org> # # Note: BusyBox init doesn't support runlevels. The runlevels field is # completely ignored by BusyBox init. If you want runlevels, use # sysvinit. # # Format for each entry: <id>:<runlevels>:<action>:<process> # # id == tty to run on, or empty for /dev/console # runlevels == ignored # action == one of sysinit, respawn, askfirst, wait, and once # process == program to run # Startup the system ::sysinit:/bin/mount -t proc proc /proc ::sysinit:/bin/mount -o remount,rw / ::sysinit:/bin/mkdir -p /dev/pts /dev/shm ::sysinit:/bin/mount -a ::sysinit:/bin/mount -t debugfs debugfs /sys/kernel/debug ::sysinit:/sbin/swapon -a null::sysinit:/bin/ln -sf /proc/self/fd /dev/fd null::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin null::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout null::sysinit:/bin/ln -sf /proc/self/fd/2 /dev/stderr ::sysinit:/bin/hostname -F /etc/hostname # now run any rc scripts ::sysinit:/etc/init.d/rcS # Put a getty on the serial port #console::respawn:/sbin/getty -L console 0 vt100 # GENERIC_SERIAL ::respawn:-/bin/sh # Stuff to do for the 3-finger salute #::ctrlaltdel:/sbin/reboot # Stuff to do before rebooting ::shutdown:/etc/init.d/rcK ::shutdown:/sbin/swapoff -a ::shutdown:/bin/umount -a -r

Spawn four consoles with servers listening for QEMU system emulation:

This uses OP-TEE’s soc_term.py

#!/bin/bash SOC_TERM=path/to/optee/soc_term.py xterm -title "Firmware" -e bash -c "$SOC_TERM 54320" & xterm -title "Secure" -e bash -c "$SOC_TERM 54321" & xterm -title "host" -e bash -c "$SOC_TERM 54322" & xterm -title "Realm" -e bash -c "$SOC_TERM 54323" & while ! nc -z 127.0.0.1 54320 || ! nc -z 127.0.0.1 54321 || ! nc -z 127.0.0.1 54322 || ! nc -z 127.0.0.1 54323; do sleep 1; done

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