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SNP Utility Script (snp.sh)

This SNP utility script is a provisioning and test script that performs three tasks:

  1. Sets up an AMD EPYC CPU powered server by building the required patched versions of qemu, ovmf and the linux kernel.

  2. Direct boot launch a SNP enabled guest with qemu.

  3. Attest the SNP guest using the virtee/snpguest CLI tool.

Tested on the following OS distributions:

  • Ubuntu 20.04
  • Ubuntu 22.04
  • RHEL 9.4

Image formats supported:

  • qcow2

WARNING: This script installs developer packages on the system it is run on. Beware and check 'install_dependencies' if there are any admin concerns.

WARNING: This script sets the default grub entry to the SNP kernel version that is built for the host in this script. Modifying the system grub can cause booting issues.

Enable Host SNP Options in the System BIOS

These options will differ depending on the server manufacturer and BIOS version. The following steps show an example of the necessary changes required for a CRB system BIOS:

CBS -> CPU Common ->
            SEV-ES ASID Space Limit -> 100
            SNP Memory Coverage -> Enabled 
            SMEE -> Enabled
    -> NBIO Common ->
            SEV-SNP -> Enabled

For more information, see the 'Enabling/Disabling SNP' section of the following document:

58207-using-sev-with-amd-epyc-processors.pdf

Using the Script Utility

Download the script and add the execute permission:

wget https://github.com/amd/sev-utils/raw/main/tools/snp.sh
chmod +x snp.sh

Setup the host by building SNP patched versions of qemu, ovmf and the linux kernel:

./snp.sh setup-host

The --non-upm option can be specified with the above command if a non-upm version of the kernel is desired.

The above step will also change the default grub entry to the newly installed host kernel.

A reboot will be necessary:

sudo reboot

When the system has finished rebooting back into the OS, launch a guest using the following command:

./snp.sh launch-guest

This will download a cloud-init ubuntu server jammy image that will be used as the guest disk. The guest is launched by passing qemu direct boot command line options for ovmf, initrd, kernel and the kernel append parameters.

The --non-upm option can be specified with the above command if a non-upm version of the kernel is desired. The setup-host command must be run with this same option if launching the guest with a non-upm kernel.

Attest the guest using the following command:

./snp.sh attest-guest

The above result will show the contents of the SNP report and perform the report signature and certificate CA verification. It uses the IBM sev-snp-measure tool to calculate the expected launch measurement by measuring the ovmf, initrd, kernel, kernel append parameters, and additional qemu command line parameters. This expected measurement is then checked and verified against the launch measurement that is output from the virtee/snpguest tool. If the two measurements match, then the test returns with a successful output.

Stopping all Guests

All script created guests can be stopped by running the following command:

./snp.sh stop-guests

BYO Image

The SNP script utility provides support for the user to provide their own image.

This image has the following requirements:

  • debian/ubuntu based
  • SSH must be installed
  • The GUEST_USER must already be added
  • The SSH public key must already be injected for the specified user
  • There must be enough space for the kernel installation

Export the following environment variables:

export IMAGE="guest.img"
export GUEST_USER="user"
export GUEST_SSH_KEY_PATH="guest-key"

IMAGE is the path to the user supplied guest image. GUEST_USER is the user required to access the guest. GUEST_SSH_KEY_PATH is the path to the SSH private key.

Launch the guest:

./snp.sh launch-guest

Accessing the Guest via SSH

Once launched, the guest can be accessed with the following SSH command:

ssh -p 10022 -i snp-guest-key amd@localhost

'10022' is the default qemu mapped port for network access. This can be changed by exporting HOST_SSH_PORT.

'snp-guest-key' is the path to the SSH private key.

'amd' is the default user to access the guest. This can be changed by exporting GUEST_USER.