Signed-off-by: Erik Skultety <eskultet@xxxxxxxxxx> --- Since v2: - incorporated Brijesh's notes into the SEV description and fixed the info about SME docs/launch_security_sev.html.in | 521 +++++++++++++++++++++++++++++++ 1 file changed, 521 insertions(+) create mode 100644 docs/launch_security_sev.html.in diff --git a/docs/launch_security_sev.html.in b/docs/launch_security_sev.html.in new file mode 100644 index 0000000000..923bb52b25 --- /dev/null +++ b/docs/launch_security_sev.html.in @@ -0,0 +1,521 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html> +<html xmlns="http://www.w3.org/1999/xhtml";> + <body> + <h1>Launch security with AMD SEV</h1> + + <ul id="toc"></ul> + + <p> + 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. + </p> + + <h2>AMD SEV</h2> + <p> + 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 + <a href="https://developer.amd.com/sev/";>AMD's developer portal</a>. + </p> + + <h2><a id="Host">Enabling SEV on the host</a></h2> + <p> + 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: + </p> + + <pre> +$ cat /proc/cpuinfo | grep sev +... +sme ssbd sev ibpb</pre> + + <p> + 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: + </p> + + <pre> +mem_encrypt=on kvm_amd.sev=1 + </pre> + + <p> + To make the changes persistent, append the above to the variable holding + parameters of the kernel command line in + <code>/etc/default/grub</code> to preserve SEV settings across reboots + </p> + + <pre> +$ cat /etc/default/grub +... +GRUB_CMDLINE_LINUX="... mem_encrypt=on kvm_amd.sev=1" +$ grub2-mkconfig -o /boot/efi/EFI/<distro>/grub.cfg</pre> + + <p> + <code>mem_encrypt=on</code> turns on the SME memory encryption feature on + the host which protects against the physical attack on the hypervisor + memory. The <code>kvm_amd.sev</code> parameter actually enables SEV in + the kvm module. It can be set on the command line alongside + <code>mem_encrypt</code> like shown above, or it can be put into a + module config under <code>/etc/modprobe.d/</code> + </p> + + <pre> +$ cat /etc/modprobe.d/sev.conf +options kvm_amd sev=1 + </pre> + + <p> + After rebooting the host, you should see SEV being enabled in the kernel: + </p> + + <pre> +$ cat /sys/module/kvm_amd/parameters/sev +1 + </pre> + + <h2><a id="Virt">Checking SEV support in the virt stack</a></h2> + <p> + <b>Note: All of the commands bellow need to be run with root privileges.</b> + </p> + + <p> + First make sure you have the following packages in the specified versions: + </p> + + <ul> + <li> + libvirt >= 4.5.0 (>5.1.0 recommended due to additional SEV bugfixes) + </li> + <li> + QEMU >= 2.12.0 + </li> + </ul> + <p> + To confirm that the virtualization stack supports SEV, run the following: + </p> + + <pre> +# virsh domcapabilities +<domainCapabilities> +... + <features> + ... + <sev supported='yes'> + <cbitpos>47</cbitpos> + <reducedPhysBits>1</reducedPhysBits> + </sev> + ... + </features> +</domainCapabilities></pre> + <p> + 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: + </p> + + <pre> +# systemctl stop libvirtd.service + </pre> + + <p> + Now you need to clean the capabilities cache: + </p> + + <pre> +# rm -f /var/cache/libvirt/qemu/capabilities/* + </pre> + + <p> + If you now restart libvirtd, it will re-probe the capabilities and if + you now run: + </p> + + <pre> +# virsh domcapabilities + </pre> + + <p> + SEV should be listed as supported. If you still see: + </p> + + <pre> +<sev supported='no'/> + </pre> + + <p> + it means one of two things: + <ol> + <li> + libvirt does support SEV, but either QEMU or the host does not + </li> + <li> + you have libvirt <=5.1.0 which suffered from getting a + <code>'Permission denied'</code> on <code>/dev/sev</code> 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 + </li> + </ol> + </p> + + <h2><a id="Configuration">VM Configuration</a></h2> + <p> + SEV is enabled in the XML by specifying the + <a href="https://libvirt.org/formatdomain.html#launchSecurity";><launchSecurity> </a> element. However, specifying <code>launchSecurity</code> isn't + enough to boot an SEV VM. Further configuration requirements are discussed + below. + </p> + + <h3><a id="Machine">Machine type</a></h3> + <p> + 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. + </p> + + <h5>Q35</h5> +<pre> +... +<os> + <type arch='x86_64' machine='pc-q35-3.0'>hvm</type> + ... +</os> +...</pre> + + <h5>i440fx (discouraged)</h5> + <pre> +... +<os> + <type arch='x86_64' machine='pc-i440fx-3.0'>hvm</type> + ... +</os> +... + </pre> + + <h3><a id="Boot">Boot loader</a></h3> + <p> + SEV is only going to work with OVMF (UEFI), so you'll need to point libvirt to + the correct OVMF binary. + </p> + <pre> +... +<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> +...</pre> + + <h3><a id="Memory">Memory</a></h3> + <p> + 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 <code><currentMemory></code> 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. + + <p> + 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: + </p> + </p> + + <pre> +# virsh edit <domain> +<domain> + ... + <currentMemory unit='KiB'>4194304</currentMemory> + <memtune> + <hard_limit unit='KiB'>4456448</hard_limit> + </memtune> + ... +</domain></pre> + <p> + There's another, preferred method of taking care of the limits by + using the<code><memoryBacking></code> element along with the + <code><locked/></code> subelement: + </p> + + <pre> +<domain> + ... + <memoryBacking> + <locked/> + </memoryBacking> + ... +</domain></pre> + + <p> + 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 <code>machine.slice</code>. + </p> + + <pre> +# systemctl set-property machine.slice MemoryHigh=<value></pre> + + <p> + To put even stricter measures in place which would involve the OOM killer, use + <pre> +# systemctl set-property machine.slice MemoryMax=<value></pre> + instead. Alternatively, you can create a systemd config (don't forget + to reload systemd configuration in this case): + <pre> +# cat << EOF > /etc/systemd/system.control/machine.slice.d/90-MemoryMax.conf +MemoryMax=<value> +EOF</pre> + The trade-off to keep in mind with the second approach is that the VMs + can still perform DoS on each other. + </p> + + <h3><a id="Virtio">Virtio</a></h3> + <p> + In order to make virtio devices work, we need to enable emulated IOMMU + on the devices so that virtual DMA can work. + </p> + + <pre> +# 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></pre> + + <p> + 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). + + <p> + Note: some devices like video devices don't + support non-transitional model, which means that virtio GPU cannot be used. + </p> + </p> + + <pre> +<domain> + ... + <devices> + ... + <memballoon model='virtio-non-transitional'> + <driver iommu='on'/> + </memballoon> + </devices> + ... +</domain></pre> + + <h2><a id="Limitations">Limitations</a></h2> + <p> + 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 <code>/dev/sev</code> 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 <code>audit2allow</code> on how to do that) or putting SELinux into permissive mode (discouraged). + </p> + + <h2><a id="Examples">Full domain XML examples</a></h2> + + <h5>Q35 machine</h5> + <pre> +<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></pre> + + <h5>PC-i440fx machine:</h5> + <pre> +<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></pre> + </body> +</html> -- 2.21.0 -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
