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Enabling AMD Secure Nested Paging (SEV-SNP) on ThinkSystem Servers

Planning / Implementation

20 Feb 2024
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10 pages, 262 KB


AMD Secure Encrypted Virtualization-Secure Nested Paging (SEV-SNP) is a feature of AMD EPYC processors that adds strong memory integrity protection to help prevent malicious hypervisor-based attacks in order to create an isolated execution environment.

This paper introduces SEV-SNP and describes how to enable the feature. The paper is for Linux administrators who want to use SEV-SNP on an AMD-based ThinkSystem server.


Trusted execution environments have become increasingly common for the execution of security critical code. In their processors, AMD first introduced Secure Encrypted Virtualization (SEV) in 2016, and then introduced Encrypted State (SEV-ES) to encrypt CPU register state of virtual machines (VM) in 2017. The third generation of SEV, Secure Nested Paging (SEV-SNP), enhances memory integrity protection for the malicious attacks from hypervisor.

SEV-SNP is supported on AMD EYPC processors starting with the AMD EPYC 7003 series processors.

AMD SEV-SNP offers powerful and flexible support for the isolation of a guest virtual machine from an untrusted host operating system. It is very useful in public cloud and any untrusted host scenario. Major public cloud vendors already used it in their products, including Amazon Web Services (AWS) and Google Cloud.

This paper describes how to enable SEV-SNP on an AMD-based ThinkSystem server running Red Hat Enterprise Linux (RHEL) 9.2.

SEV-SNP overview

This section will show how to protect the guest VM via SEV-SNP function and what threats can be prevented.

In Figure 1, “AMD Hardware and Firmware” and “SEV-SNP VM” are considered trusted in the measurement process, even though the hypervisor is untrusted.

Threat model
Figure 1. Threat model

Under the attestation process of SEV-SNP, only a guest owner (third-party) can decide whether the guest is trusted or not based on attestation reports.

Attestation Process
Figure 2. Attestation Process

Table 1 lists potential threads mitigated by SEV-SNP.

Table 1. Threat mitigation
Potential Threats Mitigated
Confidentiality VM Memory
Example attack: Hypervisor reads private VM memory
VM Register State
Example attack: Read VM register state after VMEXIT
DMA Protection
Example attack: Device attempts to read VM memory
Integrity Replay Protection
Example attack: Replace VM memory with an old copy
Data Corruption
Example attack: Replace VM memory with junk data
Memory Aliasing
Example attack: Map two guest pages to same DRAM page
Memory Re-Mapping
Example attack: Switch DRAM page mapped to a guest page
Availability Denial of Service on Hypervisor
Example attack: Malicious guest refuses to yield/exit
Physical Access Attacks Offline DRAM analysis
Example attack: Cold boot
Misc. TCB Rollback
Example attack: Revert AMD-SP firmware to old version
Malicious Interrupt/Exception Injection
Example attack: Inject interrupt while RFLAGS.IF=0
Optional mitigated
Indirect Branch Predictor Poisoning
Example attack: Poison BTB from hypervisor
Optional mitigated
Secure Hardware Debug Registers
Example attack: Change breakpoints during debug
Optional mitigated
Trusted CPUID Information
Example attack: Hypervisors lies about platform capabilities
Optional mitigated


Preparing UEFI and the Host OS

UEFI configuration via System Setup

The steps to activate SEV-SNP in UEFI are as follows:

  1. Press F1 during boot to enter System Setup
  2. In the Processors section, enable these items as shown in the figure below.
    • SVM Mode: Enable
    • SEV-SNP Support : Enable

    Processor settings in System Setup
    Figure 3. Processor settings in System Setup

  3. In the Memory section, enable these items as shown in the figure below.
    • SMEE: Enable
    • SEV-ES ASID Count: AUTO
    • SEV-ES ASID Space Limit Control: Manual
    • SEV-ES ASID Space Limit: 10
    • SEV Control: Enable

    Memory settings in System Setup
    Figure 4. Memory settings in System Setup

UEFI configuration via OneCLI

As an alternative to System Setup, you can use the OneCLI command line tool, which can be downloaded from:

  1. Create a configuration file, as follows:
    [root@sev-snp ~]# cat > snp_uefi.txt << EOF 
    set Processors.SEV-SNPSupport enable
    set Memory.SMEE Enable
    set Memory.SEVASIDCount AUTO
    set Memory.SEV-ESASIDSpaceLimitControl Manual
    set Memory.SEV-ESASIDSpaceLimit 10
    set Memory.SEVControl Enable set Processors.SVMMode Enable
    [root@sev-snp ~]#
  2. Set up UEFI config via Onecli command: 

    Issuing the OneCLI command
    Figure 5. Issuing the OneCLI command to run the configuration file

  3. Restart the server to apply the configuration.

Operating System configuration

As RHEL 9.2 inbox kernel and QEMU hypervisor still do not fully support this feature, users need to compile it by themselves. Ensure your system has access to the Internet and source code will be downloaded automatically during compiling.

  1. Register your system and enable repository “codeready-builder-for-rhel-9-x86_64-rpms" using the following commands:
    [root@sev-snp ~]# subscription-manager register --username XXX --password XXX
    This system is already registered. Use --force to override
    [root@sev-snp ~]#
    [root@sev-snp ~]# subscription-manager repos --enable codeready-builder-for-rhel-9-x86_64-rpms
  2. Install the necessary packages for compiling:
    [root@sev-snp ~]# yum install -y ninja-build.x86_64 gthread libgib* glib-devel.x86_64 \
    > PackageKit-glib.x86_64 PackageKit-glib-devel.x86_64 pixman pixman-devel.x86_64 \
    > nasm.x86_64 uuid-devel.x86_64 glibc-static acpica-tools  perl dwarves pkgconfig
    [root@sev-snp ~]# pip install meson; ln -s /usr/lib64/ /usr/lib64/; ldconfig
  3. Build Linux kernel, QEMU and other components with the following command
    # git clone
    # cd AMDSEV; git checkout snp-latest
    # ./ –package


Enabling SEV-SNP on the Host OS

Follow these steps enable and verify SEV-SNP on a host OS:

  1. Install the compiled kernel
    # cd snp-release-<DATE>
    # sudo cp kvm.conf /etc/modprobe.d/
    # rpm -ivh $(find . -name "kernel*host*" | grep -v headers)
  2. Modify the SNP kernel to the default boot entry
    # grubby --default-kernel                 # Get current default boot entry 
    # grubby --info ALL                       # Get all the boot entry
    # grubby --set-default-index=ENTRY-INDEX  # Set the SNP kernel entry index to the default
  3. Reboot the server
    # reboot
  4. Verify the feature was enabled from driver layer:
    [root@sev-snp ~]# cat /sys/module/kvm_amd/parameters/sev_snp 
    [root@sev-snp ~]#
  5. Verify the dmesg log shows the SEV-SNP support information:
    [root@sev-snp ~]# dmesg I grep SEV-SNP
    [    0.569182] SEV-SNP: RMP table physical address [0x000000009b700000 - 0x00000000a3cfffff]
    [    3.905529] ccp 0000:23:00.1: SEV-SNP API:1.55 build : 14
    [   15.047076] kvm_amd: SEV-ES and SEV-SNP supported: 9 ASIDs

Enabling SEV-SNP on a Guest OS

Follow these steps to enable and verify SEV-SNP on guest OS.

  1. Create SEV-SNP VM with the following commands
    # qemu-img create -f qcow2 /home/rh9.qcow2 40G    #Create your qcow2 file for guest storage
    # cd AMDSEV/snp-release-
    # sed -i "s/CONSOLE=.*$/CONSOLE=\"virtio\"/"
    # sed -i "s/readonly/readonly=on/"
    # ./ -hda /home/rh9.qcow2 -cdrom home/RHEL-9.2.0-20230414.17-x86_64-dvd1.iso

    Figure 6.

  2. Finish the installation via VNC viewer based on the output about VNC server address.

    Launch VNC viewer
    Figure 7. Launch VNC viewer

  3. Launch the guest OS
    # ./ -hda  /home/rh9.qcow2 -sev-snp   #Launch the guest 
  4. Access the guest via VNC viewer based on the output about VNC server address.

    Figure 8.

  5. If SEV-SNP is enabled properly in a VM, the log “Memory Encryption Features active:” must include the string “SEV-SNP” in OS log (dmesg):
    [root@snp-guest ~]# dmesg | grep -i SEV-SNP
    [    0.2712931 Memory Encryption Features active: AMD SEU SEV-ES SEV-SNP
    [root@snp-guest ~]#


Song Shang is a Linux Engineer in Lenovo Infrastructure Solutions Group, based in Beijing, China.

Thanks to the following people for their contributions to this project:

  • David Watts, Lenovo Press
  • Adrian Huang, Lenovo Linux Engineer
  • Gary Cudak, Lenovo Lead Architect

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