On 7/2/19 10:59 AM, Erik Skultety wrote: > 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 > Reviewed-by: Brijesh Singh <brijesh.singh@xxxxxxx> thanks > 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
