[PATCH] docs: Describe protected virtualization guest setup

From: Viktor Mihajlovski <mihajlov(a)linux.ibm.com&gt; Protected virtualization/IBM Secure Execution for Linux protects guest memory and state from the host. Add some basic information about technology and a brief guide on setting up secure guests with libvirt. Signed-off-by: Viktor Mihajlovski <mihajlov(a)linux.ibm.com&gt; Reviewed-by: Boris Fiuczynski <fiuczy(a)linux.ibm.com&gt; Reviewed-by: Paulo de Rezende Pinatti <ppinatti(a)linux.ibm.com&gt; --- docs/kbase.html.in | 3 + docs/kbase/protected_virtualization.rst | 188 ++++++++++++++++++++++++ 2 files changed, 191 insertions(+) create mode 100644 docs/kbase/protected_virtualization.rst diff --git a/docs/kbase.html.in b/docs/kbase.html.in index c586e0f676..05a3239224 100644 --- a/docs/kbase.html.in +++ b/docs/kbase.html.in @@ -14,6 +14,9 @@ <dt><a href="kbase/secureusage.html">Secure usage</a></dt> <dd>Secure usage of the libvirt APIs</dd> + <dt><a href="kbase/protected_virtualization.html">Protected virtualization</a></dt> + <dd>Running secure guests with IBM Secure Execution</dd> + <dt><a href="kbase/launch_security_sev.html">Launch security</a></dt> <dd>Securely launching VMs with AMD SEV</dd> diff --git a/docs/kbase/protected_virtualization.rst b/docs/kbase/protected_virtualization.rst new file mode 100644 index 0000000000..48f2add14e --- /dev/null +++ b/docs/kbase/protected_virtualization.rst @@ -0,0 +1,188 @@ +======================== +Protected Virtualization +======================== + +.. contents:: + +Overview +======== + +Protected virtualization, also known as IBM Secure Execution is a +hardware-based privacy protection technology for s390x (IBM Z). +It allows to execute virtual machines such that the host system +has no access to a VM's state and memory contents. + +Unlike other similar technologies, the memory of a running guest +is not encrypted but protected by hardware access controls, which +may only be manipulated by trusted system firmware, called +ultravisor. + +For the cases where the host needs access to guest memory (e.g. for +paging), it can request pages to be exported to it. The exported page +will be encrypted with a unique key for the running guest by the +ultravisor. The ultravisor also computes an integrity value for +the page, and stores it in a special table, together with the page +index and a counter. This way it can verify the integrity of +the page content upon re-import into the guest. + +In other cases it may be necessary for a guest to grant the host access +to dedicated memory regions (e.g. for I/O). The guest can request +that the ultravisor removes the memory protection from individual +pages, so that they can be shared with the host. Likewise, the +guest can undo the sharing. + +A secure guest will initially start in a regular non-protected VM. +The start-up is controlled by a small bootstrap program loaded +into memory together with encrypted operating system components and +a control structure (the PV header). +The operating system components (e.g. Linux kernel, initial RAM +file system, kernel parameters) are encrypted and integrity +protected. The component encryption keys and integrity values are +stored in the PV header. +The PV header is wrapped with a public key belonging to a specific +system (in fact it can be wrapped with multiple such keys). The +matching private key is only accessible by trusted hardware and +firmware in that specific system. +Consequently, such a secure guest boot image can only be run on the +systems it has been prepared for. Its contents can't be decrypted +without access to the private key and it can't be modified as +it is integrity protected. + +Host Requirements +================= + +IBM Secure Execution for Linux has some hardware and firmware +requirements. The system hardware must be an IBM z15 (or newer), +or an IBM LinuxONE III (or newer). + +It is also necessary that the IBM Secure Execution feature is +enabled for that system. Check for facility '158', e.g. + +:: + + $ grep facilities /proc/cpuinfo | grep 158 + +The kernel must include the protected virtualization support +which can be verified by checking for the presence of directory +``/sys/firmware/uv``. It will only be present when both the +hardware and the kernel support are available. + +Finally, the host operating system must donate some memory to +the ultravisor needed to store memory security information. +This is achieved by specifying the following kernel command +line parameter to the host boot configuration + +:: + + prot_virt=1 + + +Guest Requirements +================== + +Guest Boot +---------- + +To start a guest in protected virtualization secure mode, the +boot image must have been prepared first with the program +``genprotimg`` using the correct public key for this host. +``genprotimg`` is part of the package ``s390-tools``, or +``s390-utils``, depending on the Linux distribution being used. +It can also be found at +`<https://github.com/ibm-s390-tools/s390-tools/tree/master/genprotimg>`_ + +The guests have to be configured to use the host CPU model, which +must contain the ``unpack`` facility indicating ultravisor guest support. + +With the following command it's possible to check whether the host +CPU model satisfies the requirement + +:: + + $ virsh domcapabilities | grep unpack + +which should return + +:: + + <feature policy='require' name='unpack'/> + +If the check fails despite the host system actually supporting +protected virtualization guests, this can be caused by a stale +libvirt capabilities cache. To recover, run the following +commands + +:: + + $ systemctl stop libvirtd + $ rm /var/cache/libvirt/qemu/capabilities/*.xml + $ systemctl start libvirtd + + +Guest I/O +--------- + +Protected virtualization guests support I/O using virtio devices. +As the virtio datastructures of secure guests are not accessible +by the host, it is necessary to use shared memory ('bounce buffers'). + +To enable virtio devices to use shared buffers, it is necessary +to configure them with platform_iommu enabled. This can done by adding +``iommu='on'`` to the driver element of a virtio device definition in the +guest's XML, e.g. + +:: + + <interface type='network'> + <source network='default'/> + <model type='virtio'/> + <driver name='vhost' iommu='on'/> + </interface> + +It is mandatory to define all virtio bus devices in this way to +prevent the host from attempting to access protected memory. +Ballooning will not work and is fenced by QEMU. It should be +disabled by specifying + +:: + + <memballoon model='none'/> + +Finally, the guest Linux must be instructed to allocate I/O +buffers using memory shared between host and guest using SWIOTLB. +This is done by adding ``swiotlb=nnn`` to the guest's kernel command +line string, where ``nnn`` stands for the number of statically +allocated 2K entries. A commonly used value for swiotlb is 262144. + +Example guest definition +======================== + +Minimal domain XML for a protected virtualization guest, essentially +it's mostly about the ``iommu`` property + +:: + + <domain type='kvm'> + <name>protected</name> + <memory unit='KiB'>2048000</memory> + <currentMemory unit='KiB'>2048000</currentMemory> + <vcpu>1</vcpu> + <os> + <type arch='s390x'>hvm</type> + </os> + <cpu mode='host-model'/> + <devices> + <disk type='file' device='disk'> + <driver name='qemu' type='qcow2' cache='none' io='native' iommu='on'> + <source file='/var/lib/libvirt/images/protected.qcow2'/> + <target dev='vda' bus='virtio'/> + </disk> + <interface type='network'> + <driver iommu='on'/> + <source network='default'/> + <model type='virtio'/> + </interface> + <console type='pty'/> + <memballoon model='none'/> + </devices> + </domain> -- 2.25.1