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Secure Encrypted Virtualization (SEV)

SEV is an extension to the AMD-V architecture which supports running encrypted virtual machine (VMs) under the control of KVM. Encrypted VMs have their pages (code and data) secured such that only the guest itself has access to the unencrypted version. Each encrypted VM is associated with a unique encryption key; if its data is accessed by a different entity using a different key, the encrypted guests data will be incorrectly decrypted, leading to unintelligible data.

SEV support has been accepted in upstream projects. This repository provides scripts to build various components to enable SEV support until the distros pick the newer version of components.

To enable SEV support we need the following versions.

Project Version
kernel >= 4.16
libvirt >= 4.5
qemu >= 2.12
ovmf >= commit (75b7aa9528bd 2018-07-06 )

To enable SEV-ES support we need the following versions.

Project Version/Tag
kernel >= 5.11
libvirt >= 4.5
qemu >= 6.00
ovmf >= edk2-stable202102

  • Installing newer libvirt may conflict with existing setups hence script does not install the newer version of libvirt. If you are interested in launching SEV guest through the virsh commands then build and install libvirt 4.5 or higher. Use LaunchSecurity tag https://libvirt.org/formatdomain.html#sev for creating the SEV enabled guest.

  • SEV support is not available in SeaBIOS. Guest must use OVMF.

SLES-15

SUSE Linux Enterprise Server 15 GA includes SEV support; we do not need to compile the sources.

SLES-15 does not contain the updated libvirt packages yet hence we will use QEMU command line interface to launch VMs.

Prepare Host OS

SEV is not enabled by default, lets enable it through kernel command line:

Append the following in /etc/defaults/grub

GRUB_CMDLINE_LINUX_DEFAULT=".... kvm_amd.sev=1"

Regenerate grub.cfg and reboot the host

# grub2-mkconfig -o /boot/efi/EFI/sles/grub.cfg
# reboot

Install the qemu launch script. The launch script can be obtained from this project.

# git clone https://github.com/AMDESE/AMDSEV.git
# cd AMDSEV/distros/sles-15
# ./build.sh

Prepare VM image

Create empty virtual disk image

# qemu-img create -f qcow2 sles-15.qcow2 30G

Create a new copy of OVMF_VARS.fd. The OVMF_VARS.fd is a "template" used to emulate persistent NVRAM storage. Each VM needs a private, writable copy of VARS.fd.

#cp /usr/share/qemu/ovmf-x86_64-suse-4m-vars.bin OVMF_VARS.fd

Download and install sles-15 guest

# launch-qemu.sh -hda sles-15.qcow2 -cdrom SLE-15-Installer-DVD-x86_64-GM-DVD1.iso -nosev

Follow the screen to complete the guest installation.

Launch VM

Use the following command to launch SEV guest

# launch-qemu.sh -hda sles-15.qcow2

NOTE: when guest is booting, CTRL-C is mapped to CTRL-], use CTRL-] to stop the guest

RHEL-8

RedHat Enterprise Linux 8.0 GA includes SEV support; we do not need to compile the sources.

Prepare Host OS

SEV is not enabled by default, lets enable it through kernel command line:

Append the following in /etc/defaults/grub

GRUB_CMDLINE_LINUX_DEFAULT=".... kvm_amd.sev=1"

Regenerate grub.cfg and reboot the host

# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
# reboot

Install the qemu launch script. The launch script can be obtained from this project.

# git clone https://github.com/AMDESE/AMDSEV.git
# cd AMDSEV/distros/rhel-8
# ./build.sh

Prepare VM image

Create empty virtual disk image

# qemu-img create -f qcow2 rhel-8.qcow2 30G

Create a new copy of OVMF_VARS.fd. The OVMF_VARS.fd is a "template" used to emulate persistent NVRAM storage. Each VM needs a private, writable copy of VARS.fd.

#cp /usr/share/OVMF/OVMF_VARS.fd OVMF_VARS.fd

Download and install rhel-8 guest

# launch-qemu.sh -hda rhel-8.qcow2 -cdrom RHEL-8.0.0-20190404.2-x86_64-dvd1.iso

Follow the screen to complete the guest installation.

Launch VM

Use the following command to launch SEV guest

# launch-qemu.sh -hda rhel-8.qcow2

NOTE: when guest is booting, CTRL-C is mapped to CTRL-], use CTRL-] to stop the guest

Fedora-28

Fedora-28 includes newer kernel and ovmf packages but has older qemu. We will need to update the QEMU to launch SEV guest.

Prepare Host OS

SEV is not enabled by default, lets enable it through kernel command line:

Append the following in /etc/defaults/grub

GRUB_CMDLINE_LINUX_DEFAULT=".... kvm_amd.sev=1"

Regenerate grub.cfg and reboot the host

# grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg
# reboot

Build and install newer qemu

# cd distros/fedora-28
# ./build.sh

Prepare VM image

Create empty virtual disk image

# qemu-img create -f qcow2 fedora-28.qcow2 30G

Create a new copy of OVMF_VARS.fd. The OVMF_VARS.fd is a "template" used to emulate persistent NVRAM storage. Each VM needs a private, writable copy of VARS.fd.

# cp /usr/share/OVMF/OVMF_VARS.fd OVMF_VARS.fd

Download and install fedora-28 guest

# launch-qemu.sh -hda fedora-28.qcow2 -cdrom  Fedora-Workstation-netinst-x86_64-28-1.1.iso

Follow the screen to complete the guest installation.

Launch VM

Use the following command to launch SEV guest

# launch-qemu.sh -hda fedora-28.qcow2

NOTE: when guest is booting, CTRL-C is mapped to CTRL-], use CTRL-] to stop the guest

Fedora-29

Fedora-29 contains all the pre-requisite packages to launch an SEV guest. But the SEV feature is not enabled by default, this section documents how to enable the SEV feature.

Prepare Host OS

  • Add new udev rule for the /dev/sev device

    # cat /etc/udev/rules.d/71-sev.rules
KERNEL=="sev", MODE="0660", GROUP="kvm"

  • Clean libvirt caches so that on restart libvirt re-generates the capabilities

    # rm -rf /var/cache/libvirt/qemu/capabilities/

  • The default FC-29 kernel (4.18) has SEV disabled in config files, but the kernel available through the FC-29 update has SEV config set

    Use the following command to upgrade the packages and also install the virtulization packages

    # yum groupinstall virtualization
# yum upgrade

  • By default SEV is disabled, append the following in /etc/defaults/grub

     GRUB_CMDLINE_LINUX_DEFAULT=".... kvm_amd.sev=1"

    Regenerate grub.cfg and reboot the host

     # grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg
 # reboot

  • Install the qemu launch script

     # cd distros/fedora-29
 # ./build.sh

Prepare VM image

Create empty virtual disk image

# qemu-img create -f qcow2 fedora-29.qcow2 30G

Create a new copy of OVMF_VARS.fd. The OVMF_VARS.fd is a "template" used to emulate persistent NVRAM storage. Each VM needs a private, writable copy of VARS.fd.

# cp /usr/share/edk2/ovmf/OVMF_VARS.fd OVMF_VARS.fd

Download and install fedora-29 guest

# launch-qemu.sh -hda fedora-29.qcow2 -cdrom  Fedora-Workstation-netinst-x86_64-29-1.1.iso

Follow the screen to complete the guest installation.

Launch VM

Use the following command to launch SEV guest

# launch-qemu.sh -hda fedora-29.qcow2

NOTE: when guest is booting, CTRL-C is mapped to CTRL-], use CTRL-] to stop the guest

Ubuntu 18.04

Ubuntu 18.04 does not includes the newer version of components to be used as SEV hypervisor hence we will build and install newer kernel, qemu, ovmf.

Prepare Host OS

  • Enable source repositories See

  • Build and install newer components

# cd distros/ubuntu-18.04
# ./build.sh

Prepare VM image

Create empty virtual disk image

# qemu-img create -f qcow2 ubuntu-18.04.qcow2 30G

Create a new copy of OVMF_VARS.fd. The OVMF_VARS.fd is a "template" used to emulate persistent NVRAM storage. Each VM needs a private, writable copy of VARS.fd.

# cp /usr/local/share/qemu/OVMF_VARS.fd OVMF_VARS.fd

Install ubuntu-18.04 guest

# launch-qemu.sh -hda ubuntu-18.04.qcow2 -cdrom ubuntu-18.04-desktop-amd64.iso

Follow the screen to complete the guest installation.

Launch VM

Use the following command to launch SEV guest

# launch-qemu.sh -hda ubuntu-18.04.qcow2

NOTE: when guest is booting, CTRL-C is mapped to CTRL-], use CTRL-] to stop the guest

openSUSE-Tumbleweed

Latest version of openSUSE Tumbleweed distro contains all the pre-requisite packages to launch an SEV guest. But the SEV feature is not enabled by default, this section documents how to enable the SEV feature.

Prepare Host OS

  • Add new udev rule for the /dev/sev device

    # cat /etc/udev/rules.d/71-sev.rules
KERNEL=="sev", MODE="0660", GROUP="kvm"

  • Clean libvirt caches so that on restart libvirt re-generates the capabilities

    # rm -rf /var/cache/libvirt/qemu/capabilities/
# systemctl restart libvirtd

  • SEV feature is not enabled in kernel by default, lets enable it through kernel command line:

    Append the following in /etc/defaults/grub

     GRUB_CMDLINE_LINUX_DEFAULT=".... kvm_amd.sev=1"

    Regenerate grub.cfg and reboot the host

    # grub2-mkconfig -o /boot/efi/EFI/opensuse/grub.cfg
# reboot

Launch SEV VM

The SEV support is available in the latest libvirt, follow the https://libvirt.org/kbase/launch_security_sev.html to use the libvirt to create and manage the SEV guest.

SEV Containers

Container runtimes that use hardware virtualization to further isolate container workloads can also make use of SEV. As a proof-of-concept, the kata branch contains an SEV-capable version of the Kata Containers runtime that will start all containers inside of SEV virtual machines.

For installation instructions on Ubuntu systems, see the README.

Additional Resources

SME/SEV white paper

SEV API Spec

APM Section 15.34

KVM forum slides

KVM forum videos

Linux kernel

Linux kernel

Libvirt LaunchSecurity tag

Libvirt SEV

Libvirt SEV domainCap

Qemu doc

FAQ

  • How do I know if hypervisor supports SEV feature ?

    a) When using libvirt >= 4.15 run the following command

    # virsh domcapabilities

    If hypervisor supports SEV feature then sev tag will be present.

    See Libvirt DomainCapabilities feature for additional information.

    b) Use qemu QMP 'query-sev-capabilities' command to check the SEV support. If SEV is supported then command will return the full SEV capabilities (which includes host PDH, cert-chain, cbitpos and reduced-phys-bits).

    See QMP doc for details on how to interact with QMP shell.

  • How do I know if SEV is enabled in the guest ?

    a) Check the kernel log buffer for the following message

    # dmesg | grep -i sev
AMD Secure Encrypted Virtualization (SEV) active

    b) MSR 0xc0010131 (MSR_AMD64_SEV) can be used to determine if SEV is active

    # rdmsr -a 0xc0010131

    Bit[0]:   0 = SEV is not active
          1 = SEV is active

  • Can I use virt-manager to launch SEV guest?

    virt-manager uses libvirt to manage VMs, SEV support has been added in libvirt but virt-manager does use the newly introduced LaunchSecurity tags yet hence we will not able to launch SEV guest through the virt-manager.

    If your system is using libvirt >= 4.15 then you can manually edit the xml file to use LaunchSecurity to enable the SEV support in the guest.

  • How to increase SWIOTLB limit ?

When SEV is enabled, all the DMA operations inside the guest are performed on the shared memory. Linux kernel uses SWIOTLB bounce buffer for DMA operations inside SEV guest. A guest panic will occur if kernel runs out of the SWIOTLB pool. Linux kernel default to 64MB SWIOTLB pool. It is recommended to increase the swiotlb pool size to 512MB. The swiotlb pool size can be increased in guest by appending the following in the grub.cfg file

Append the following in /etc/defaults/grub

GRUB_CMDLINE_LINUX_DEFAULT=".... swiotlb=262144"

And regenerate the grub.cfg.

  • SWIOTLB allocation failure causing kernel panic

SWIOTLB size, when not specifically specified, is automatically calculated based on the amount of guest memory, up to 1GB maximum. However, the guest may not have enough contiguous memory below 4GB to satisify the SWIOTLB allocation requirement, in which case the kernel will panic:

 [    0.004318] software IO TLB: SWIOTLB bounce buffer size adjusted to 965MB
 ...
 [    1.015953] Kernel panic - not syncing: Can not allocate SWIOTLB buffer earlier and can't now provide you with the DMA bounce buffer

In this situation, please specify the SWIOTLB size, as shown in How to increase SWIOTLB limit, to a value that allows the guest to boot.

  • virtio-blk device runs out-of-dma-buffer error

To support the multiqueue mode, virtio-blk drivers inside the guest allocates large number of DMA buffer. SEV guest uses SWIOTLB for the DMA buffer allocation or mapping hence kernel runs of the SWIOTLB pool quickly and triggers the out-of-memory error. In those cases consider increasing the SWIOTLB pool size or use virtio-scsi device.

  • SEV_INIT fails with error 0x13

The error 0x13 is a defined as HWERROR_PLATFORM in the SEV specification. The error indicates that memory encryption support is not enabled in the host BIOS. Look for the SMEE setting in your BIOS menu and explicitly enable it. You can verify that SMEE is enabled on your machine by running the below command

$ sudo modprobe msr
$ sudo rdmsr  0xc0010010
3f40000

Verify that BIT23 is memory encryption (aka SMEE) is set.

  • SEV Firmware Updates

SEV firmware is part of the AMD Secure Processor and is responsible for much of the life cycle management of an SEV guest. Updates to the firmware can be made available outside the traditional BIOS update path.

On Linux, the AMD Secure Processor driver (ccp) is responsible for updating the SEV firmware when the driver is loaded. The driver searches for the firmware using the kernel's firmware loading interface. The kernel's firmware loading interface will search for the firmware, by name, in a number of locations (see fw_search_path.rst), with the traditional path being /lib/firmware.

The ccp driver searches for three different possible SEV firmware files under the "amd" directory, using the first file that is found. The first file that is searched for is a firmware file with a CPU family and model specific name, then a firmware file with a CPU family and model range name, and finally a generic name. The naming convention uses the following format:

  • Model specific: amd_sev_famXXh_modelYYh.sbin

    • where XX is the hex representation of the CPU family
    • where YY is the hex representation of the CPU model

  • Range specific: amd_sev_famXXh_modelYxh.sbin

    • where XX is the hex representation of the CPU family
    • where Y is the hex representation of the first digit of the CPU model

  • Generic: sev.fw

For example, for an EPYC processor with a family of 0x19 and a model of 0x01, the search order would be::

  1. amd/amd_sev_fam19h_model01h.sbin
  2. amd/amd_sev_fam19h_model0xh.sbin
  3. amd/sev.fw

The level of firmware that is loaded can be viewed in the kernel log. For example, issuing the command "dmesg | grep ccp":

[   13.879283] ccp 0000:01:00.5: enabling device (0000 -> 0002)
[   13.887532] ccp 0000:01:00.5: sev enabled
[   13.899646] ccp 0000:01:00.5: psp enabled
[   14.560461] ccp 0000:01:00.5: SEV API:1.55 build:24
[   14.644793] ccp 0000:01:00.5: SEV-SNP API:1.55 build:24

Since, on Linux, the firmware is updated on driver load of the ccp module, it is possible to update the firmware level after the system has booted. At this time, all guests would need to be shutdown and the kvm_amd module unloaded before the ccp module could be unloaded and reloaded.

SEV firmware can be obtained from the AMD Secure Encrypted Virtualization web portal or through the Linux Firmware repository.