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Linux SVSM (Secure VM Service Module)

** The Linux SVSM project is no longer being actively developed. Users of Linux SVSM should switch over to the COCONUT SVSM project. **

Table of contents

  1. What is this magic?
  2. Preparing the host
  3. Installation
  4. Running Linux SVSM
  5. Contribution
  6. Linux SVSM userspace
  7. Authors and License

What is this magic? <a name="introduction"></a>

Linux SVSM (Secure VM Service Module) implements a guest communication interface so that VM guests can offload sensitive operations (for example, updating access permissions on protected pages) onto a privileged* guest acting as service module. Linux SVSM relies on AMD's Secure Nested Paging (SNP) and prior Secure Encrypted Virtualization technologies (See SEV documentation).

The idea is that Linux SVSM will not only offload security operations, but will also be able to provide other services such as live VM migration; the privilege separation model of SVSM permits the existence of a virtual Trusted Platform Module (virtual TPM).

* AMD SNP introduces the Virtual Machine Privilege Level (VMPLs) for enhanced security control. VMPL0 is the highest level of privilege. Linux SVSM runs at VMPL 0, as opposed to other guests running under VMPL >=1. Certain operations become architecturally impossible to guests running at lower privilege levels (e.g. use of the PVALIDATE instruction and certain forms of RMPADJUST).

Generate and read source code documentation with:

# make doc

which will also install necessary prerequisites.

Preparing the host <a name="host"></a>

Linux SVSM assumes a host with support for AMD's SEV-SNP, as well as compatible guest, Qemu and OVMF BIOS. We provide bash scripts to automate the installation process of these prerequisites. The remainder of these instructions were tested on Ubuntu 22.04 server, installed with kernel 5.15.0-46-generic.

Start by verifying that the following BIOS settings are enabled. The settings may vary depending on the vendor BIOS. The menu options below are from AMD's BIOS.

  CBS -> CPU Common ->
                SEV-ES ASID space Limit Control -> Manual
                SEV-ES ASID space limit -> 100
                SNP Memory Coverage -> Enabled
                SMEE -> Enabled
      -> NBIO common ->
                SEV-SNP -> Enabled

We now need to build the host and guest kernels, Qemu and OVMF BIOS used for launching the SEV-SNP guest.

$ cd scripts/
$ ./build.sh --package

If build fails, read subsection Build troubleshooting. On successful build, the binaries will be available in snp-release-<DATE>.

Now we need to install the Linux kernel on the host machine:

$ cd snp-release-<date>
$ sudo ./install.sh

Reboot the machine and choose SNP Host kernel from the grub menu. You can check you have a kernel with the proper SNP support with:

$ sudo dmesg | grep SEV
[    7.393321] SEV-SNP: RMP table physical address 0x0000000088a00000 - 0x00000000a8ffffff
[   18.958687] ccp 0000:22:00.1: SEV firmware update successful
[   21.081484] ccp 0000:22:00.1: SEV-SNP API:1.51 build:3
[   21.286378] SEV supported: 255 ASIDs
[   21.290367] SEV-ES and SEV-SNP supported: 254 ASIDs

Build troubleshooting <a name="trouble-build"></a>

The most likely source of build errors is missing a tool. Try installing the following:

$ sudo apt install make ninja-build libglib2.0-dev libpixman-1-dev python3
$ sudo apt install nasm iasl flex bison libelf-dev libssl-dev

If your error is during OVMF's compilation, you can try getting a verbose form of the error, running manually with -v. In our case:

$ cd ovmf
$ source edksetup.sh
$ nice build -v -q --cmd-len=64436 -DDEBUG_ON_SERIAL_PORT -n 32 -t GCC5 -a X64 -p OvmfPkg/OvmfPkgX64.dsc

If your error involves still not finding Python, you may try to replace python with python3 in the file BaseTools/Tests/GNUmakefile of the ovmf folder that you have just cloned.

Installation <a name="install"></a>

Linux SVSM requires the Rust nightly tool-chain, as well as components that can be downloaded from rustup. The process can be automated with:

# make prereq

You can select default installation for rustup. After that, make sure rust-lld can be found in your PATH. You can edit your ~/.bashrc with:

export PATH="/(YOUR PATH)/rustlib/x86_64-unknown-linux-gnu/bin/:$PATH"

To build:

# make

To build with serial output progress information, for debugging:

# make FEATURES=verbose

You should NEVER have to specify the cargo target, as we have .cargo/config.toml. The Makefile includes a basic clean target. To force prerequisites re-installation on the next execution of make do:

# make superclean

To run the unit tests:

# make test

Running Linux SVSM <a name="run"></a>

The building process will generate svsm.bin that can be passed to Qemu (svsm parameter). Inside directory scripts/ we provide launch-qemu.sh to ease the execution of the Qemu virtual machine. First, we need an empty virtual disk image and distribution (in our example, Ubuntu):

# qemu-img create -f qcow2 guest.qcow2 30G
# wget <link-to-iso> ubuntu.iso

Once we have an image prepared, we can boot with the command below. In the Grub option of installation, you can edit the linux kernel command adding 'console=tty0 console=ttyS0,115200n8' and then Ctr+X.

# ./launch-qemu.sh -hda guest.qcow2 -cdrom ubuntu.iso

after that, we can simply boot and install the kernel *.debs/*.rpms from within the guest VM.

[host@snp-host ~]#  ./launch-qemu.sh -hda guest.qcow2
[guest@snp-guest ~]# scp host@ip:/<dir>/scripts/linux/<version>*guest*.deb .
[guest@snp-guest ~]# chmod +x *.deb && dpkg -i *.deb
[guest@snp-guest ~]# reboot

Finally, we will have to execute the script again, this time providing the SVSM binary. Once the SVSM guest is up, you can check it is running on VMPL1 (lower privilege level) with:

[host@snp-host ~]#  ./launch-qemu.sh -hda guest.qcow2 -sev-snp -svsm svsm.bin
[guest@snp-guest ~]# dmesg | grep VMPL
[    1.264552] SEV: SNP running at VMPL1.

Note: The launch-qemu.sh script was updated to support the newer UPM-based SEV-SNP support. If you are running on an older SEV-SNP host kernel that doesn't support UPM, please add the -noupm parameter to the launch command:

[host@snp-host ~]#  ./launch-qemu.sh -hda guest.qcow2 -sev-snp -svsm svsm.bin -noupm

By default, SVSM lives at 512 GB (SVSM_GPA), and has 256 MB of memory (SVSM_MEM). This can be changed at compilation. For example:

# make SVSM_GPA=0x90000000 SVSM_MEM=0x20000000

The SVSM page table applies an offset to its virtual addresses.

Linux SVSM userspace <a name="cpl3"></a>

Linux SVSM's main branch does not contain support for userspace (CPL3). If interested, checkout branch cpl-support.

Contribution <a name="contribute"></a>

Please read CONTRIBUTING.md for instructions on contribution and style.

Authors and License <a name="authors"></a>

The original authors and maintainers of this software are:

and they will act as reviewers for future contributions.

Other developers have made substantial contributions to this project, to obtain the full list, please refer to the Contributors page or review the authorship information in the project's source code headers.

Linux SVSM is distributed under the MIT license. For more information, read file LICENSE. To obtain information about the crates that Linux SVSM depends on, you can run:

$./scripts/crates.sh