A micro hypervisor for RISC-V systems.

Quick Start

Building

rustup target add riscv64gc-unknown-none-elf
make salus

Note that Salus relies on unstable features from the nightly toolchain so there may be build breakages from time-to-time. Try running rustup upgrade first should you run into build failures.

Running

The Makefile provides targets for running various hosts in QEMU.

Prerequisites

Toolchains:

• Rust: Install rustup, then: rustup target add riscv64gc-unknown-none-elf
• GCC: Install gcc-riscv64-unknown-elf

QEMU:

• Out-of-tree patches are required; see table below.
• Build using QEMU instructions with --target-list=riscv64-softmmu
• Set the QEMU= variable to point to the compiled QEMU tree when using the make run_* targets described below.

Linux kernel:

• Out-of-tree patches are required; see table below.
• Build: ARCH=riscv CROSS_COMPILE=riscv64-unknown-linux-gnu- make defconfig Image
• Set the LINUX= variable to point to the compiled Linux kernel tree when using linux related targets described below.

Buildroot:

• Out-of-tree patches are required; see table below.
• Build: make qemu_riscv64_virt_defconfig && make
• Set the BUILDROOT= variable to point to the buildroot source directory while running make run_buildroot targets described below.

Debian:

• Download and extract a pre-baked riscv64-virt image from https://people.debian.org/~gio/dqib/.
• Set the DEBIAN= variable to point to the extracted archive when using the make run_debian target described below.

Latest known-working branches:

Project	Branch
QEMU	https://github.com/rivosinc/qemu/tree/salus-integration-10312022
Linux	https://github.com/rivosinc/linux/tree/salus-integration-10312022
Buildroot	https://github.com/rivosinc/buildroot/tree/salus-integration-2022.08.2

Linux VM

The make run_linux target will boot a bare Linux kernel as the host VM that will panic upon reaching init due to the lack of a root filesystem.

To boot a more functional Linux VM, use the make run_debian target which will boot a Debian VM with emulated storage and network devices using pre-baked Debian initrd and rootfs images.

Example:

make run_debian \
    QEMU=<path-to-qemu-tree> \
    LINUX=<path-to-linux-tree> \
    DEBIAN=<path-to-pre-baked-image>

To boot a quick functional Linux VM with busybox based rootfs built from buildroot, use the make run_buildroot target. The above buildroot tree must be compiled to generate the rootfs with networking enabled.

Example:

make run_buildroot \
    QEMU=<path-to-qemu-tree> \
    LINUX=<path-to-linux-tree> \
    BUILDROOT=<path-to-buildroot repo>

Once booted, the VM can be SSH'ed into with root:root at localhost:7722.

Additional emulated devices may be added with the EXTRA_QEMU_ARGS Makefile variable. Note that only PCI devices using MSI/MSI-X will be usable by the VM. virtio-pci devices may also be used with iommu_platform=on,disable-legacy=on flags.

Example:

make run_debian ... \
     EXTRA_QEMU_ARGS="-device virtio-net-pci,iommu_platform=on,disable-legacy=on"

Test VM

A pair of test VMs are located in test-workloads.

tellus is a target build with make tellus that runs in VS mode and provides the ability to send test API calls to salus running in HS mode.

guestvm is a test confidential guest. It is started by tellus and used for testing the guest side of the TSM API.

A makefile shortcut is provided:

make run_tellus \
    QEMU=<path-to-qemu-tree>

This will build salus, tellus, and the guestvm then boot them with the system-installed qemu.

Overview - Initial prototype

  +---U-mode--+ +-----VS-mode-----+ +-VS-mode-+
  |           | |                 | |         |
  |           | | +---VU-mode---+ | |         |
  |   Salus   | | | VMM(crosvm) | | |  Guest  |
  | Delegated | | +-------------+ | |         |
  |   Tasks   | |                 | |         |
  |           | |    Host(linux)  | |         |
  +-----------+ +-----------------+ +---------+
        |                |               |
   TBD syscall      SBI (TH-API)    SBI(TG-API)
        |                |               |
  +-------------HS-mode-----------------------+
  |       Salus                               |
  +-------------------------------------------+
                         |
                        SBI
                         |
  +----------M-mode---------------------------+
  |       Firmware(OpenSBI)                   |
  +-------------------------------------------+

Host

Normally Linux, this is the primary operating system for the device running in VS mode.

Responsibilities:

• Scheduling
• Memory allocation (except memory kept by firmware and salus at boot)
• Guest VM start/stop/scheduling via TEE TH-API provided by salus
• Device drivers and delegation

VMM

The virtual machine manager that runs in userspace of the host.

• qemu/kvm or crosvm
• configures memory and devices for guests
• runs any virtualized or para virtualized devices
• runs guests with vcpu_run.

Guests

VS-mode operating systems started by the host.

• Can run confidential or shared workloads.
• Uses memory shared from or donated by the host
• scheduled by the host
• can start sub-guests
• Confidential guests use TG-API for salus/host services

Salus

The code in this repository. An HS-mode hypervisor.

• starts the host and guests
• manages stage-2 translations and IOMMU configuration for guest isolation
• delegates some tasks such as attestation to u-mode helpers
• measured by the trusted firmware/RoT

Firmware

M-mode code.

OpenSBI currently boots salus from the memory (0x80200000) where qemu loader loaded it and passes the device tree to Salus.

The above instructions use OpenSBI inbuilt in Qemu. If OpenSBI needs to be built from scratch, fw_dynamic should be used for -bios argument in the qemu commandline.

Vectors

Salus is able to detect if the CPU supports the vector extension. The same binary will run on processors with or without the exension, and will enable vector code if it is present.