From f0bfb1b892cf028967348016ae42b411698d9996 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Wed, 20 Nov 2019 14:05:50 +0000 Subject: [PATCH] docs: convert kbase/launch_security_sev.html.in to RST MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This is a semi-automated conversion. The first conversion is done using "pandoc -f html -t rst". The result is then editted manually to apply the desired heading markup, and fix a few things that pandoc gets wrong. Reviewed-by: Michal Privoznik Signed-off-by: Daniel P. Berrangé --- docs/kbase/launch_security_sev.html.in | 533 ------------------------- docs/kbase/launch_security_sev.rst | 529 ++++++++++++++++++++++++ 2 files changed, 529 insertions(+), 533 deletions(-) delete mode 100644 docs/kbase/launch_security_sev.html.in create mode 100644 docs/kbase/launch_security_sev.rst diff --git a/docs/kbase/launch_security_sev.html.in b/docs/kbase/launch_security_sev.html.in deleted file mode 100644 index 985c11a47b..0000000000 --- a/docs/kbase/launch_security_sev.html.in +++ /dev/null @@ -1,533 +0,0 @@ - - - - -

Launch security with AMD SEV

- -
    - -

    - Storage encryption in modern public cloud computing is a common practice. - However, from the point of view of a user of these cloud workloads, a - significant amount of trust needs to be put in the cloud platform security as - well as integrity (was the hypervisor tampered?). For this reason there's ever - rising demand for securing data in use, i.e. memory encryption. - One of the solutions addressing this matter is AMD SEV. -

    - -

    AMD SEV

    -

    - SEV (Secure Encrypted Virtualization) is a feature extension of AMD's SME (Secure - Memory Encryption) intended for KVM virtual machines which is supported - primarily on AMD's EPYC CPU line. In contrast to SME, SEV uses a unique memory encryption - key for each VM. The whole encryption of memory pages is completely transparent - to the hypervisor and happens inside dedicated hardware in the on-die memory controller. - Each controller includes a high-performance Advanced Encryption Standard - (AES) engine that encrypts data when it is written to DRAM and decrypts it - when read. - - For more details about the technology itself, you can visit - AMD's developer portal. -

    - -

    Enabling SEV on the host

    -

    - Before VMs can make use of the SEV feature you need to make sure your - AMD CPU does support SEV. You can check whether SEV is among the CPU - flags with: -

    - - 
    -$ cat /proc/cpuinfo | grep sev
-...
-sme ssbd sev ibpb
    - -

    - Next step is to enable SEV in the kernel, because it is disabled by default. - This is done by putting the following onto the kernel command line: -

    - - 
    -mem_encrypt=on kvm_amd.sev=1
-
    - -

    - To make the changes persistent, append the above to the variable holding - parameters of the kernel command line in - /etc/default/grub to preserve SEV settings across reboots -

    - - 
    -$ cat /etc/default/grub
-...
-GRUB_CMDLINE_LINUX="... mem_encrypt=on kvm_amd.sev=1"
-$ grub2-mkconfig -o /boot/efi/EFI/<distro>/grub.cfg
    - -

    - mem_encrypt=on turns on the SME memory encryption feature on - the host which protects against the physical attack on the hypervisor - memory. The kvm_amd.sev parameter actually enables SEV in - the kvm module. It can be set on the command line alongside - mem_encrypt like shown above, or it can be put into a - module config under /etc/modprobe.d/ -

    - - 
    -$ cat /etc/modprobe.d/sev.conf
-options kvm_amd sev=1
-
    - -

    - After rebooting the host, you should see SEV being enabled in the kernel: -

    - - 
    -$ cat /sys/module/kvm_amd/parameters/sev
-1
-
    - -

    Checking SEV support in the virt stack

    -

    - Note: All of the commands bellow need to be run with root privileges. -

    - -

    - First make sure you have the following packages in the specified versions: -

    - -
      -
    • - libvirt >= 4.5.0 (>5.1.0 recommended due to additional SEV bugfixes) -
      • -
    • - QEMU >= 2.12.0 -
      • -
    -

    - To confirm that the virtualization stack supports SEV, run the following: -

    - - 
    -# virsh domcapabilities
-<domainCapabilities>
-...
-  <features>
-    ...
-    <sev supported='yes'>
-      <cbitpos>47</cbitpos>
-      <reducedPhysBits>1</reducedPhysBits>
-    </sev>
-    ...
-  </features>
-</domainCapabilities>
    -

    - Note that if libvirt was already installed and libvirtd running before enabling SEV in the kernel followed by the host reboot you need to force libvirtd - to re-probe both the host and QEMU capabilities. First stop libvirtd: -

    - - 
    -# systemctl stop libvirtd.service
-
    - -

    - Now you need to clean the capabilities cache: -

    - - 
    -# rm -f /var/cache/libvirt/qemu/capabilities/*
-
    - -

    - If you now restart libvirtd, it will re-probe the capabilities and if - you now run: -

    - - 
    -# virsh domcapabilities
-
    - -

    - SEV should be listed as supported. If you still see: -

    - - 
    -<sev supported='no'/>
-
    - -

    - it means one of two things: -

      -
    1. - libvirt does support SEV, but either QEMU or the host does not -
      2. -
    2. - you have libvirt <=5.1.0 which suffered from getting a - 'Permission denied' on /dev/sev because - of the default permissions on the character device which prevented - QEMU from opening it during capabilities probing - you can either - manually tweak the permissions so that QEMU has access to it or - preferably install libvirt 5.1.0 or higher -
      3. -
    -

    - -

    VM Configuration

    -

    - SEV is enabled in the XML by specifying the - <launchSecurity> element. However, specifying launchSecurity isn't - enough to boot an SEV VM. Further configuration requirements are discussed - below. -

    - -

    Machine type

    -

    - Even though both Q35 and legacy PC machine types (for PC see also - "virtio") can be used with SEV, usage of the legacy PC machine type is - strongly discouraged, since depending on how your OVMF package was - built (e.g. including features like SecureBoot or SMM) Q35 may even be - required. -

    - -
    Q35
    -
    -...
-<os>
-  <type arch='x86_64' machine='pc-q35-3.0'>hvm</type>
-  ...
-</os>
-...
    - -
    i440fx (discouraged)
    - 
    -...
-<os>
-  <type arch='x86_64' machine='pc-i440fx-3.0'>hvm</type>
-  ...
-</os>
-...
-
    - -

    Boot loader

    -

    - SEV is only going to work with OVMF (UEFI), so you'll need to point libvirt to - the correct OVMF binary. -

    - 
    -...
-<os>
-  <type arch='x86_64' machine='pc-q35-3.0'>hvm</type>
-  <loader readonly='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.fd</loader>
-</os>
-...
    - -

    Memory

    -

    - Internally, SEV expects that the encrypted memory pages won't be swapped out or move - around so the VM memory needs to be pinned in physical RAM which will be - handled by QEMU. Apart from that, certain memory regions allocated by QEMU - itself (UEFI pflash, device ROMs, video RAM, etc.) have to be encrypted as - well. This causes a conflict in how libvirt tries to protect the host. - By default, libvirt enforces a memory hard limit on each VM's cgroup in order - to protect the host from malicious QEMU to allocate and lock all the available - memory. This limit corresponds to the total memory allocation for the VM given - by <currentMemory> element. However, trying to account for the additional - memory regions QEMU allocates when calculating the limit in an automated manner - is non-deterministic. One way to resolve this is to set the hard limit manually. - -

    - Note: Figuring out the right number so that your guest boots and isn't killed is - challenging, but 256MiB extra memory over the total guest RAM should suffice for - most workloads and may serve as a good starting point. - - For example, a domain with 4GB memory with a 256MiB extra hard limit would look - like this: -

    -

    - - 
    -# virsh edit <domain>
-<domain>
-  ...
-  <currentMemory unit='KiB'>4194304</currentMemory>
-  <memtune>
-    <hard_limit unit='KiB'>4456448</hard_limit>
-  </memtune>
-  ...
-</domain>
    -

    - There's another, preferred method of taking care of the limits by - using the<memoryBacking> element along with the - <locked/> subelement: -

    - - 
    -<domain>
-  ...
-  <memoryBacking>
-    <locked/>
-  </memoryBacking>
-  ...
-</domain>
    - -

    - What that does is that it tells libvirt not to force any hard limit (well, - unlimited) upon the VM cgroup. The obvious advantage is that one doesn't need - to determine the hard limit for every single SEV-enabled VM. However, there is - a significant security-related drawback to this approach. Since no hard limit - is applied, a malicious QEMU could perform a DoS attack by locking all of the - host's available memory. The way to avoid this issue and to protect the host is - to enforce a bigger hard limit on the master cgroup containing all of the VMs - - on systemd this is machine.slice. -

    - - 
    -# systemctl set-property machine.slice MemoryHigh=<value>
    - -

    - To put even stricter measures in place which would involve the OOM killer, use - 

    -# systemctl set-property machine.slice MemoryMax=<value>
    - instead. Alternatively, you can create a systemd config (don't forget - to reload systemd configuration in this case): - 
    -# cat << EOF > /etc/systemd/system.control/machine.slice.d/90-MemoryMax.conf
-MemoryMax=<value>
-EOF
    - The trade-off to keep in mind with the second approach is that the VMs - can still perform DoS on each other. -

    - -

    Virtio

    -

    - In order to make virtio devices work, we need to enable emulated IOMMU - on the devices so that virtual DMA can work. -

    - - 
    -# virsh edit <domain>
-<domain>
-  ...
-  <controller type='virtio-serial' index='0'>
-    <driver iommu='on'/>
-  </controller>
-  <controller type='scsi' index='0' model='virtio-scsi'>
-    <driver iommu='on'/>
-  </controller>
-  ...
-  <memballoon model='virtio'>
-    <driver iommu='on'/>
-  </memballoon>
-  <rng model='virtio'>
-    <backend model='random'>/dev/urandom</backend>
-    <driver iommu='on'/>
-  </rng>
-  ...
-<domain>
    - -

    - If you for some reason want to use the legacy PC machine type, further changes - to the virtio - configuration is required, because SEV will not work with Virtio <1.0. In - libvirt, this is handled by using the virtio-non-transitional device model - (libvirt >= 5.2.0 required). - -

    - Note: some devices like video devices don't - support non-transitional model, which means that virtio GPU cannot be used. -

    -

    - - 
    -<domain>
-  ...
-  <devices>
-    ...
-    <memballoon model='virtio-non-transitional'>
-      <driver iommu='on'/>
-    </memballoon>
-  </devices>
-  ...
-</domain>
    - -

    Checking SEV from within the guest

    -

    - After making the necessary adjustments discussed in - Configuration, the VM should now boot - successfully with SEV enabled. You can then verify that the guest has - SEV enabled by running: -

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

    Limitations

    -

    - Currently, the boot disk cannot be of type virtio-blk, instead, virtio-scsi - needs to be used if virtio is desired. This limitation is expected to be lifted - with future releases of kernel (the kernel used at the time of writing the - article is 5.0.14). - If you still cannot start an SEV VM, it could be because of wrong SELinux label on the /dev/sev device with selinux-policy <3.14.2.40 which prevents QEMU from touching the device. This can be resolved by upgrading the package, tuning the selinux policy rules manually to allow svirt_t to access the device (see audit2allow on how to do that) or putting SELinux into permissive mode (discouraged). -

    - -

    Full domain XML examples

    - -
    Q35 machine
    - 
    -<domain type='kvm'>
-  <name>sev-dummy</name>
-  <memory unit='KiB'>4194304</memory>
-  <currentMemory unit='KiB'>4194304</currentMemory>
-  <memoryBacking>
-    <locked/>
-  </memoryBacking>
-  <vcpu placement='static'>4</vcpu>
-  <os>
-    <type arch='x86_64' machine='pc-q35-3.0'>hvm</type>
-    <loader readonly='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.fd</loader>
-    <nvram>/var/lib/libvirt/qemu/nvram/sev-dummy_VARS.fd</nvram>
-  </os>
-  <features>
-    <acpi/>
-    <apic/>
-    <vmport state='off'/>
-  </features>
-  <cpu mode='host-model' check='partial'>
-    <model fallback='allow'/>
-  </cpu>
-  <clock offset='utc'>
-    <timer name='rtc' tickpolicy='catchup'/>
-    <timer name='pit' tickpolicy='delay'/>
-    <timer name='hpet' present='no'/>
-  </clock>
-  <on_poweroff>destroy</on_poweroff>
-  <on_reboot>restart</on_reboot>
-  <on_crash>destroy</on_crash>
-  <pm>
-    <suspend-to-mem enabled='no'/>
-    <suspend-to-disk enabled='no'/>
-  </pm>
-  <devices>
-    <emulator>/usr/bin/qemu-kvm</emulator>
-    <disk type='file' device='disk'>
-      <driver name='qemu' type='qcow2'/>
-      <source file='/var/lib/libvirt/images/sev-dummy.qcow2'/>
-      <target dev='sda' bus='scsi'/>
-      <boot order='1'/>
-    </disk>
-    <controller type='virtio-serial' index='0'>
-      <driver iommu='on'/>
-    </controller>
-    <controller type='scsi' index='0' model='virtio-scsi'>
-      <driver iommu='on'/>
-    </controller>
-    <interface type='network'>
-      <mac address='52:54:00:cc:56:90'/>
-      <source network='default'/>
-      <model type='virtio'/>
-      <driver iommu='on'/>
-    </interface>
-    <graphics type='spice' autoport='yes'>
-      <listen type='address'/>
-      <gl enable='no'/>
-    </graphics>
-    <video>
-      <model type='qxl'/>
-    </video>
-    <memballoon model='virtio'>
-      <driver iommu='on'/>
-    </memballoon>
-    <rng model='virtio'>
-      <driver iommu='on'/>
-    </rng>
-  </devices>
-  <launchSecurity type='sev'>
-    <cbitpos>47</cbitpos>
-    <reducedPhysBits>1</reducedPhysBits>
-    <policy>0x0003</policy>
-  </launchSecurity>
-</domain>
    - -
    PC-i440fx machine:
    - 
    -<domain type='kvm'>
-  <name>sev-dummy-legacy</name>
-  <memory unit='KiB'>4194304</memory>
-  <currentMemory unit='KiB'>4194304</currentMemory>
-  <memtune>
-    <hard_limit unit='KiB'>5242880</hard_limit>
-  </memtune>
-  <vcpu placement='static'>4</vcpu>
-  <os>
-    <type arch='x86_64' machine='pc-i440fx-3.0'>hvm</type>
-    <loader readonly='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.fd</loader>
-    <nvram>/var/lib/libvirt/qemu/nvram/sev-dummy_VARS.fd</nvram>
-    <boot dev='hd'/>
-  </os>
-  <features>
-  <acpi/>
-  <apic/>
-  <vmport state='off'/>
-  </features>
-  <cpu mode='host-model' check='partial'>
-    <model fallback='allow'/>
-  </cpu>
-  <clock offset='utc'>
-    <timer name='rtc' tickpolicy='catchup'/>
-    <timer name='pit' tickpolicy='delay'/>
-    <timer name='hpet' present='no'/>
-  </clock>
-  <on_poweroff>destroy</on_poweroff>
-  <on_reboot>restart</on_reboot>
-  <on_crash>destroy</on_crash>
-  <pm>
-    <suspend-to-mem enabled='no'/>
-    <suspend-to-disk enabled='no'/>
-  </pm>
-  <devices>
-    <emulator>/usr/bin/qemu-kvm</emulator>
-    <disk type='file' device='disk'>
-      <driver name='qemu' type='qcow2'/>
-      <source file='/var/lib/libvirt/images/sev-dummy-seabios.qcow2'/>
-      <target dev='sda' bus='sata'/>
-    </disk>
-    <interface type='network'>
-      <mac address='52:54:00:d8:96:c8'/>
-      <source network='default'/>
-      <model type='virtio-non-transitional'/>
-    </interface>
-    <serial type='pty'>
-      <target type='isa-serial' port='0'>
-        <model name='isa-serial'/>
-      </target>
-    </serial>
-    <console type='pty'>
-      <target type='serial' port='0'/>
-    </console>
-    <input type='tablet' bus='usb'>
-      <address type='usb' bus='0' port='1'/>
-    </input>
-    <input type='mouse' bus='ps2'/>
-    <input type='keyboard' bus='ps2'/>
-    <graphics type='spice' autoport='yes'>
-      <listen type='address'/>
-      <gl enable='no'/>
-    </graphics>
-    <video>
-      <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
-    </video>
-    <memballoon model='virtio-non-transitional'>
-      <driver iommu='on'/>
-    </memballoon>
-      <rng model='virtio-non-transitional'>
-    <driver iommu='on'/>
-    </rng>
-  </devices>
-  <launchSecurity type='sev'>
-    <cbitpos>47</cbitpos>
-    <reducedPhysBits>1</reducedPhysBits>
-    <policy>0x0003</policy>
-  </launchSecurity>
-</domain>
    - - diff --git a/docs/kbase/launch_security_sev.rst b/docs/kbase/launch_security_sev.rst new file mode 100644 index 0000000000..65f258587d --- /dev/null +++ b/docs/kbase/launch_security_sev.rst @@ -0,0 +1,529 @@ +============================ +Launch security with AMD SEV +============================ + +.. contents:: + +Storage encryption in modern public cloud computing is a common +practice. However, from the point of view of a user of these cloud +workloads, a significant amount of trust needs to be put in the cloud +platform security as well as integrity (was the hypervisor tampered?). +For this reason there's ever rising demand for securing data in use, +i.e. memory encryption. One of the solutions addressing this matter is +AMD SEV. + +AMD Secure Encrypted Virtualization (SEV) +========================================= + +SEV (Secure Encrypted Virtualization) is a feature extension of AMD's +SME (Secure Memory Encryption) intended for KVM virtual machines which +is supported primarily on AMD's EPYC CPU line. In contrast to SME, SEV +uses a unique memory encryption key for each VM. The whole encryption of +memory pages is completely transparent to the hypervisor and happens +inside dedicated hardware in the on-die memory controller. Each +controller includes a high-performance Advanced Encryption Standard +(AES) engine that encrypts data when it is written to DRAM and decrypts +it when read. For more details about the technology itself, you can +visit `AMD's developer portal `__. + +Enabling SEV on the host +======================== + +Before VMs can make use of the SEV feature you need to make sure your +AMD CPU does support SEV. You can check whether SEV is among the CPU +flags with: + +:: + + $ cat /proc/cpuinfo | grep sev + ... + sme ssbd sev ibpb + +Next step is to enable SEV in the kernel, because it is disabled by +default. This is done by putting the following onto the kernel command +line: + +:: + + mem_encrypt=on kvm_amd.sev=1 + +To make the changes persistent, append the above to the variable holding +parameters of the kernel command line in ``/etc/default/grub`` to +preserve SEV settings across reboots + +:: + + $ cat /etc/default/grub + ... + GRUB_CMDLINE_LINUX="... mem_encrypt=on kvm_amd.sev=1" + $ grub2-mkconfig -o /boot/efi/EFI//grub.cfg + +``mem_encrypt=on`` turns on the SME memory encryption feature on the +host which protects against the physical attack on the hypervisor +memory. The ``kvm_amd.sev`` parameter actually enables SEV in the kvm +module. It can be set on the command line alongside ``mem_encrypt`` like +shown above, or it can be put into a module config under +``/etc/modprobe.d/`` + +:: + + $ cat /etc/modprobe.d/sev.conf + options kvm_amd sev=1 + +After rebooting the host, you should see SEV being enabled in the +kernel: + +:: + + $ cat /sys/module/kvm_amd/parameters/sev + 1 + + +Checking SEV support in the virt stack +====================================== + +**Note: All of the commands bellow need to be run with root +privileges.** + +First make sure you have the following packages in the specified +versions: + +- libvirt >= 4.5.0 (>5.1.0 recommended due to additional SEV bugfixes) +- QEMU >= 2.12.0 + +To confirm that the virtualization stack supports SEV, run the +following: + +:: + + # virsh domcapabilities + + ... + + ... + + 47 + 1 + + ... + + + +Note that if libvirt was already installed and libvirtd running before +enabling SEV in the kernel followed by the host reboot you need to force +libvirtd to re-probe both the host and QEMU capabilities. First stop +libvirtd: + +:: + + # systemctl stop libvirtd.service + +Now you need to clean the capabilities cache: + +:: + + # rm -f /var/cache/libvirt/qemu/capabilities/* + +If you now restart libvirtd, it will re-probe the capabilities and if +you now run: + +:: + + # virsh domcapabilities + +SEV should be listed as supported. If you still see: + +:: + + + +it means one of two things: + +#. libvirt does support SEV, but either QEMU or the host does not +#. you have libvirt <=5.1.0 which suffered from getting a + ``'Permission denied'`` on ``/dev/sev`` because of the default + permissions on the character device which prevented QEMU from opening + it during capabilities probing - you can either manually tweak the + permissions so that QEMU has access to it or preferably install + libvirt 5.1.0 or higher + +VM Configuration +================ + +SEV is enabled in the XML by specifying the +` `__ +element. However, specifying ``launchSecurity`` isn't enough to boot an +SEV VM. Further configuration requirements are discussed below. + +Machine type +------------ + +Even though both Q35 and legacy PC machine types (for PC see also +"virtio") can be used with SEV, usage of the legacy PC machine type is +strongly discouraged, since depending on how your OVMF package was built +(e.g. including features like SecureBoot or SMM) Q35 may even be +required. + +Q35 +~~~ + +:: + + ... + + hvm + ... + + ... + +i440fx (discouraged) +~~~~~~~~~~~~~~~~~~~~ + +:: + + ... + + hvm + ... + + ... + +Boot loader +----------- + +SEV is only going to work with OVMF (UEFI), so you'll need to point +libvirt to the correct OVMF binary. + +:: + + ... + + hvm + /usr/share/edk2/ovmf/OVMF_CODE.fd + + ... + +Memory +------ + +Internally, SEV expects that the encrypted memory pages won't be swapped +out or move around so the VM memory needs to be pinned in physical RAM +which will be handled by QEMU. Apart from that, certain memory regions +allocated by QEMU itself (UEFI pflash, device ROMs, video RAM, etc.) +have to be encrypted as well. This causes a conflict in how libvirt +tries to protect the host. By default, libvirt enforces a memory hard +limit on each VM's cgroup in order to protect the host from malicious +QEMU to allocate and lock all the available memory. This limit +corresponds to the total memory allocation for the VM given by +```` element. However, trying to account for the +additional memory regions QEMU allocates when calculating the limit in +an automated manner is non-deterministic. One way to resolve this is to +set the hard limit manually. + +Note: Figuring out the right number so that your guest boots and isn't +killed is challenging, but 256MiB extra memory over the total guest RAM +should suffice for most workloads and may serve as a good starting +point. For example, a domain with 4GB memory with a 256MiB extra hard +limit would look like this: + +:: + + # virsh edit + + ... + 4194304 + + 4456448 + + ... + + +There's another, preferred method of taking care of the limits by using +the\ ```` element along with the ```` +subelement: + +:: + + + ... + + + + ... + + +What that does is that it tells libvirt not to force any hard limit +(well, unlimited) upon the VM cgroup. The obvious advantage is that one +doesn't need to determine the hard limit for every single SEV-enabled +VM. However, there is a significant security-related drawback to this +approach. Since no hard limit is applied, a malicious QEMU could perform +a DoS attack by locking all of the host's available memory. The way to +avoid this issue and to protect the host is to enforce a bigger hard +limit on the master cgroup containing all of the VMs - on systemd this +is ``machine.slice``. + +:: + + # systemctl set-property machine.slice MemoryHigh= + +To put even stricter measures in place which would involve the OOM +killer, use + +:: + + # systemctl set-property machine.slice MemoryMax= + +instead. Alternatively, you can create a systemd config (don't forget to +reload systemd configuration in this case): + +:: + + # cat << EOF > /etc/systemd/system.control/machine.slice.d/90-MemoryMax.conf + MemoryMax= + EOF + +The trade-off to keep in mind with the second approach is that the VMs +can still perform DoS on each other. + +Virtio +------ + +In order to make virtio devices work, we need to enable emulated IOMMU +on the devices so that virtual DMA can work. + +:: + + # virsh edit + + ... + + + + + + + ... + + + + + /dev/urandom + + + ... + + +If you for some reason want to use the legacy PC machine type, further +changes to the virtio configuration is required, because SEV will not +work with Virtio <1.0. In libvirt, this is handled by using the +virtio-non-transitional device model (libvirt >= 5.2.0 required). + +Note: some devices like video devices don't support non-transitional +model, which means that virtio GPU cannot be used. + +:: + + + ... + + ... + + + + + ... + + +Checking SEV from within the guest +================================== + +After making the necessary adjustments discussed in +`Configuration <#Configuration>`__, the VM should now boot successfully +with SEV enabled. You can then verify that the guest has SEV enabled by +running: + +:: + + # dmesg | grep -i sev + AMD Secure Encrypted Virtualization (SEV) active + +Limitations +=========== + +Currently, the boot disk cannot be of type virtio-blk, instead, +virtio-scsi needs to be used if virtio is desired. This limitation is +expected to be lifted with future releases of kernel (the kernel used at +the time of writing the article is 5.0.14). If you still cannot start an +SEV VM, it could be because of wrong SELinux label on the ``/dev/sev`` +device with selinux-policy <3.14.2.40 which prevents QEMU from touching +the device. This can be resolved by upgrading the package, tuning the +selinux policy rules manually to allow svirt_t to access the device (see +``audit2allow`` on how to do that) or putting SELinux into permissive +mode (discouraged). + +Full domain XML examples +======================== + +Q35 machine +----------- + +:: + + + sev-dummy + 4194304 + 4194304 + + + + 4 + + hvm + /usr/share/edk2/ovmf/OVMF_CODE.fd + /var/lib/libvirt/qemu/nvram/sev-dummy_VARS.fd + + + + + + + + + + + + + + + destroy + restart + destroy + + + + + + /usr/bin/qemu-kvm + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 47 + 1 + 0x0003 + + + +PC-i440fx machine +----------------- + +:: + + + sev-dummy-legacy + 4194304 + 4194304 + + 5242880 + + 4 + + hvm + /usr/share/edk2/ovmf/OVMF_CODE.fd + /var/lib/libvirt/qemu/nvram/sev-dummy_VARS.fd + + + + + + + + + + + + + + + + destroy + restart + destroy + + + + + + /usr/bin/qemu-kvm + + + + + + + + + + + + + + + + + + + +
    + + + + + + + + + + + + + + + + + 47 + 1 + 0x0003 + +