% Support statement for this release
This document describes the support status and in particular the security support status of the Xen branch within which you find it.
See the bottom of the file for the definitions of the support status levels etc.
Xen-Version: 4.20-unstable
Initial-Release: n/a
Supported-Until: TBD
Security-Support-Until: Unreleased - not yet security-supported
Release Notes : RN
EXPERT and DEBUG Kconfig options are not security supported. Other Kconfig options are supported, if the related features are marked as supported in this document.
Status: Supported
Status, Xeon Phi: Not supported.
Status: Supported
Status, Xen in AArch64 mode: Supported
Status, Xen in AArch32 mode: Tech Preview
Status, Xen in Armv8-R: Experimental
Status, Cortex A57 r0p0-r1p1: Supported, not security supported
Status, Cortex A77 r0p0-r1p0: Supported, not security supported
For the Cortex A57 r0p0 - r1p1, see Errata 832075. For the Cortex A77 r0p0 - r1p0, see Errata 1508412.
Status, x86: Experimental
Status, x86: Supported up to 12 TiB. Hosts with more memory are supported, but not security supported.
Status, Arm32: Supported up to 12 GiB
Status, Arm64: Supported up to 2 TiB
Status, x86: Supported
Status, x86: Supported up to 4096
Status, ARM: Supported up to 128
Status, x86 PV: Supported
Status, ARM: Experimental
Status, x86: Supported
Status, Arm64: Supported
Status, x86: Experimental
Status, Arm64: Experimental
Status: Tech Preview
Status, AMD IOMMU: Supported
Status, Intel VT-d: Supported
Status, ARM SMMUv1: Supported, not security supported
Status, ARM SMMUv2: Supported, not security supported
Status, ARM SMMUv3: Tech Preview
Status, Renesas IPMMU-VMSA: Supported, not security supported
GICv3 is an interrupt controller specification designed by Arm.
Status, Arm64: Security supported
Status, Arm32: Supported, not security supported
Extension to the GICv3 interrupt controller to support MSI.
Status: Experimental
Enable partial emulation of registers, otherwise considered unimplemented, that would normally trigger a fault injection.
Status: Supported, with caveats
Only the following system registers are security supported:
- MDCCSR_EL0
- DBGDTR_EL0
- DBGDTRTX_EL0
- DBGDTRRX_EL0
- DBGDSCRINT
- DBGDTRTXINT
- DBGDTRRXINT
Arm64 domains can use Scalable Vector Extension (SVE/SVE2).
Status: Tech Preview
Traditional Xen PV guest
No hardware requirements
Status, x86_64: Supported
Status, x86_32, shim: Supported
Status, x86_32, without shim: Supported, not security supported
Fully virtualised guest using hardware virtualisation extensions
Requires hardware virtualisation support (Intel VMX / AMD SVM)
Status, domU: Supported
PVH is a next-generation paravirtualized mode designed to take advantage of hardware virtualization support when possible. During development this was sometimes called HVMLite or PVHv2.
Requires hardware virtualisation support (Intel VMX / AMD SVM).
Dom0 support requires an IOMMU (Intel VT-d / AMD IOMMU).
Status, domU: Supported
Status, dom0: Supported, with caveats
PVH dom0 hasn't received the same test coverage as PV dom0, so it can exhibit unexpected behavior or issues on some hardware.
At least the following features are missing on a PVH dom0:
-
PCI SR-IOV and Resizable BARs.
-
Native NMI forwarding (nmi=dom0 command line option).
-
MCE handling.
-
PCI Passthrough to any kind of domUs.
ARM only has one guest type at the moment
Status: Supported
Status, x86: Supported up to 8 TiB. Guests with more memory, but less than 16 TiB, are supported, but not security supported.
Status, Arm32: Supported up to 12 GiB
Status, Arm64: Supported up to 1 TiB
Status: Supported
Status: Supported
Status: Supported
While 32-bit builds of the tool stack are generally supported, restrictions apply in particular when running on top of a 64-bit hypervisor. For example, very large guests aren't expected to be manageable in this case. This includes guests giving the appearance of being large, by altering their own memory layouts.
Status: Supported
Format which the toolstack accepts for direct-boot kernels
Supported, x86: bzImage, ELF
Supported, ARM32: zImage
Supported, ARM64: Image
Status, SysV: Supported
Status, systemd: Supported
Status, BSD-style: Supported
Output of information in machine-parseable JSON format
Status: Experimental
Status, Linux: Supported
Status: Supported
Status: Supported
Go (golang) bindings for libxl
Status: Experimental
Support for running qemu-xen device model in a linux stubdomain.
Status: Tech Preview
Status: Supported
Status, Liveupdate: Tech Preview
Status: Supported
Status, untrusted driver domains: Supported, not security supported
Status, Liveupdate: Not functional
Status: Supported, Security support external
Status, NS16550: Supported
Status, EHCI: Supported
Status, Cadence UART (ARM): Supported
Status, PL011 UART (ARM): Supported
Status, Exynos 4210 UART (ARM): Supported
Status, OMAP UART (ARM): Supported
Status, SCI(F) UART: Supported
These are functions triggered either from the host serial console, or via the xl 'debug-keys' command, which cause Xen to dump various hypervisor state to the console.
Status: Supported, not security supported
Xen command-line flag to force synchronous console output.
Status: Supported, not security supported
Useful for debugging, but not suitable for production environments due to incurred overhead.
Status, x86: Supported, not security supported
Debugger to debug ELF guests
Soft-reset allows a new kernel to start 'from scratch' with a fresh VM state, but with all the memory from the previous state of the VM intact. This is primarily designed to allow "crash kernels", which can do core dumps of memory to help with debugging in the event of a crash.
Status: Supported
Tool to capture Xen trace buffer data
Status, x86: Supported
Export hypervisor coverage data suitable for analysis by gcov or lcov.
Status: Supported, Not security supported
Support for using Intel Processor Trace technology to trace guests from dom0.
Status, x86: Tech Preview
Allows a guest to add or remove memory after boot-time. This is typically done by a guest kernel agent known as a "balloon driver".
Status: Supported
This is a mechanism that allows normal operating systems with only a balloon driver to boot with memory < maxmem.
Status, x86 HVM: Supported
Static allocation refers to domains for which memory areas are pre-defined by configuration using physical address ranges.
Status, ARM: Tech Preview
Allow reserving parts of RAM through the device tree using physical address ranges as heap.
Status, ARM: Tech Preview
Allow sharing of identical pages between guests
Status, x86 HVM: Experimental
Allow to statically set up shared memory on dom0less system, enabling domains to do shm-based communication
Status, ARM: Tech Preview
Allow pages belonging to guests to be paged to disk
Status, x86 HVM: Experimental
Alternative p2m (altp2m) allows external monitoring of guest memory by maintaining multiple physical to machine (p2m) memory mappings.
Status, x86 HVM: Tech Preview
Status, ARM: Tech Preview
Groups physical cpus into distinct groups called "cpupools", with each pool having the capability of using different schedulers and scheduling properties.
Status: Supported
Allows to group virtual cpus into virtual cores which are scheduled on the physical cores. This results in never running different guests at the same time on the same physical core.
Status, x86: Experimental
A weighted proportional fair share virtual CPU scheduler. This is the default scheduler.
Status: Supported
A general purpose scheduler for Xen, designed with particular focus on fairness, responsiveness, and scalability
Status: Supported
A soft real-time CPU scheduler built to provide guaranteed CPU capacity to guest VMs on SMP hosts
Status: Experimental
A periodically repeating fixed timeslice scheduler.
Status: Supported
Currently only single-vcpu domains are supported.
A very simple, very static scheduling policy that always schedules the same vCPU(s) on the same pCPU(s). It is designed for maximum determinism and minimum overhead on embedded platforms and the x86 PV shim.
Status: Experimental
Status, x86/shim: Supported
Enables NUMA aware scheduling in Xen
Status, x86: Supported
NB that this refers to the ability of guests to have higher-level page table entries point directly to memory, improving TLB performance. On ARM, and on x86 in HAP mode, the guest has whatever support is enabled by the hardware.
This feature is independent of the ARM "page granularity" feature (see below).
Status, x86 HVM/PVH, HAP: Supported
Status, x86 HVM/PVH, Shadow, 2MiB: Supported
Status, ARM: Supported
On x86 in shadow mode, only 2MiB (L2) superpages are available; furthermore, they do not have the performance characteristics of hardware superpages.
This is a useful label for a set of hypervisor features which add paravirtualized functionality to HVM guests for improved performance and scalability. This includes exposing event channels to HVM guests.
Status: Supported
Status: Experimental
Status: Experimental
Forward Machine Check Exceptions to appropriate guests
Status: Supported
Guest-side driver capable of speaking the Xen PV block protocol
Status, Linux: Supported
Status, FreeBSD: Supported, Security support external
Status, NetBSD: Supported, Security support external
Status, OpenBSD: Supported, Security support external
Status, Windows: Supported, with caveats
Windows frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Guest-side driver capable of speaking the Xen PV networking protocol
Status, Linux: Supported
Status, FreeBSD: Supported, Security support external
Status, NetBSD: Supported, Security support external
Status, OpenBSD: Supported, Security support external
Status, Windows: Supported, with caveats
Windows frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Guest-side driver capable of speaking the Xen PV Framebuffer protocol
Status, Linux (xen-fbfront): Supported, with caveats
Linux frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Guest-side driver capable of speaking the Xen PV display protocol
Status, Linux, outside of "backend allocation" mode: Supported, with caveats
Status, Linux, "backend allocation" mode: Experimental
Linux frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Guest-side driver capable of speaking the Xen PV console protocol
Status, Linux (hvc_xen): Supported
Status, FreeBSD: Supported, Security support external
Status, NetBSD: Supported, Security support external
Status, Windows: Supported, with caveats
Windows frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Guest-side driver capable of speaking the Xen PV keyboard protocol. Note that the "keyboard protocol" includes mouse / pointer / multi-touch support as well.
Status, Linux (xen-kbdfront): Supported, with caveats
Linux frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Status, Linux: Supported, with caveats
Linux frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Status, Linux: Supported, with caveats
NB that while the PV SCSI frontend is in Linux and tested regularly, there is currently no xl support.
Linux frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
Guest-side driver capable of speaking the Xen PV TPM protocol
Status, Linux (xen-tpmfront): Tech Preview
Guest-side driver capable of speaking the Xen 9pfs protocol
Status, Linux: Tech Preview
Guest-side driver capable of making pv system calls
Status, Linux: Tech Preview
Guest-side driver capable of speaking the Xen PV sound protocol
Status, Linux: Supported, with caveats
Linux frontend currently trusts the backend; bugs in the frontend which allow backend to cause mischief will not be considered security vulnerabilities.
For host-side virtual device support, "Supported" and "Tech preview" include xl/libxl support unless otherwise noted.
Host-side implementations of the Xen PV block protocol.
Status, Linux (xen-blkback): Supported
Status, QEMU (xen_disk), raw format: Supported
Status, QEMU (xen_disk), qcow format: Supported
Status, QEMU (xen_disk), qcow2 format: Supported
Status, QEMU (xen_disk), vhd format: Supported
Status, FreeBSD (blkback): Supported, Security support external
Status, NetBSD (xbdback): Supported, security support external
Status, Blktap2, raw format: Deprecated
Status, Blktap2, vhd format: Deprecated
Backends only support raw format unless otherwise specified.
Host-side implementations of Xen PV network protocol
Status, Linux (xen-netback): Supported
Status, FreeBSD (netback): Supported, Security support external
Status, NetBSD (xennetback): Supported, Security support external
Host-side implementation of the Xen PV framebuffer protocol
Status, QEMU: Supported
Host-side implementation of the Xen PV console protocol
Status: Supported
Host-side implementation of the Xen PV keyboard protocol. Note that the "keyboard protocol" includes mouse / pointer support as well.
Status, QEMU: Supported
Host-side implementation of the Xen PV USB protocol
Status, QEMU: Supported
Status, Linux: Experimental
NB that while the PV SCSI backend is in Linux and tested regularly, there is currently no xl support.
Status: Tech Preview
Status, QEMU: Tech Preview
Status, xen-9pfsd: Experimental
Status, Linux: Experimental
PVCalls backend has been checked into Linux, but has no xl support.
Status: Supported
"Driver domains" means allowing non-Domain 0 domains with access to physical devices to act as back-ends.
Status: Supported, with caveats
See the appropriate "Device Passthrough" section for more information about security support.
Status: Supported, with caveats
Vulnerabilities of a device model stub domain to a hostile driver domain (either compromised or untrusted) are excluded from security support.
Status, Linux dom0: Tech Preview, with limited support
This means adding extra restrictions to a device model in order to prevent a compromised device model from attacking the rest of the domain it's running in (normally dom0).
"Tech preview with limited support" means we will not issue XSAs for the additional functionality provided by the feature; but we will issue XSAs in the event that enabling this feature opens up a security hole that would not be present without the feature disabled.
For example, while this is classified as tech preview, a bug in libxl which failed to change the user ID of QEMU would not receive an XSA, since without this feature the user ID wouldn't be changed. But a change which made it possible for a compromised guest to read arbitrary files on the host filesystem without compromising QEMU would be issued an XSA, since that does weaken security.
Status: Experimental
Status, x86: Supported
Status, ARM: Experimental
Compile time disabled for ARM by default.
Status, x86: Supported, not security supported
XSM is a security policy framework. The dummy implementation is covered by this statement, and implements a policy whereby dom0 is all powerful. See below for alternative modules (FLASK, SILO).
Status: Supported
Status: Experimental
Compile time disabled by default.
Also note that using FLASK to delegate various domain control hypercalls to particular other domains, rather than only permitting use by dom0, is also specifically excluded from security support for many hypercalls. Please see XSA-77 for more details.
Status: Experimental
The default policy includes FLASK labels and roles for a "typical" Xen-based system with dom0, driver domains, stub domains, domUs, and so on.
SILO extends the dummy policy by enforcing that DomU-s can only communicate with Dom0, yet not with each other.
Status: Supported
This means running a Xen hypervisor inside an HVM domain on a Xen system, with support for PV L2 guests only (i.e., hardware virtualization extensions not provided to the guest).
Status, x86 Xen HVM: Tech Preview
This works, but has performance limitations because the L1 dom0 can only access emulated L1 devices.
Xen may also run inside other hypervisors (KVM, Hyper-V, VMWare), but nobody has reported on performance.
This means providing hardware virtulization support to guest VMs allowing, for instance, a nested Xen to support both PV and HVM guests. It also implies support for other hypervisors, such as KVM, Hyper-V, Bromium, and so on as guests.
Status, x86 HVM: Experimental
Virtual Performance Management Unit
Status, x86 HVM: Supported, Not security supported
Status, ARM: Experimental
On ARM, support for accessing PMU registers from the guests. There is no interrupt support and Xen will not save/restore the register values on context switches.
Disabled by default. On ARM, enable with guest parameter. On x86, enable with hypervisor command line option.
This feature is not security supported: see https://xenbits.xen.org/xsa/advisory-163.html
Status: Tech Preview
Status, x86 PV: Supported, with caveats
Status, x86 HVM: Supported, with caveats
Only systems using IOMMUs are supported.
Passing through of devices sharing resources with another device is not security supported. Such sharing could e.g. be the same line interrupt being used by multiple devices, one of which is to be passed through, or two such devices having memory BARs within the same 4k page.
Not compatible with migration, populate-on-demand, altp2m, introspection, memory sharing, or memory paging.
Because of hardware limitations (affecting any operating system or hypervisor), it is generally not safe to use this feature to expose a physical device to completely untrusted guests. However, this feature can still confer significant security benefit when used to remove drivers and backends from domain 0 (i.e., Driver Domains).
An IOREQ server provides emulated devices to HVM and PVH guests. QEMU is normally the only IOREQ server, but Xen has support for multiple IOREQ servers. This allows for custom or proprietary device emulators to be used in addition to QEMU.
Status: Experimental
Status: Tech Preview
Status: Supported, not security supported
Note that this still requires an IOMMU that covers the DMA of the device to be passed through.
Status: Supported, with caveats
No support for QEMU backends in a 16K or 64K domain.
Status, Arm64: Tech Preview
There are still some code paths where a vCPU may hog a pCPU longer than necessary. The FF-A mediator is not yet implemented for Arm32. Part of the FF-A specification is not supported, see the top comment in xen/arch/arm/tee/ffa.c for limitations.
Status: Supported
Add/Remove device tree nodes using a device tree overlay binary (.dtbo).
Status, ARM: Experimental
Status: Supported
Status: Tech Preview
This section describes supported devices available in HVM mode using a qemu devicemodel (the default).
Status: Support scope restricted
Note that other devices are available but not security supported.
Status, piix3: Supported
Status, e1000: Supported
Status, rtl8193: Supported
Status, virtio-net: Supported
Status, piix3 ide: Supported
Status, ahci: Supported
See the section Blkback for image formats supported by QEMU.
Status, cirrus-vga: Supported
Status, stdvga: Supported
Status, sb16: Supported
Status, es1370: Supported
Status, ac97: Supported
Status, usbmouse: Supported
Status, usbtablet: Supported
Status, ps/2 keyboard: Supported
Status, ps/2 mouse: Supported
Status, UART 16550A: Supported
Status: Supported, not security supported
The Xen Project provides an old version of qemu with modifications
which enable use as a device model stub domain. The old version is
normally selected by default only in a stub dm configuration, but it
can be requested explicitly in other configurations, for example in
xl with device_model_version="QEMU_XEN_TRADITIONAL".
Status, Device Model Stub Domains: Supported, with caveats
Status, as host process device model: No security support, not recommended
qemu-xen-traditional is security supported only for those available devices which are supported for mainstream QEMU (see above), with trusted driver domains (see Device Model Stub Domains).
Booting a guest via PXE.
Status: Supported, with caveats
PXE inherently places full trust of the guest in the network, and so should only be used when the guest network is under the same administrative control as the guest itself.
Booting a guest via guest BIOS firmware
Status, SeaBIOS (qemu-xen): Supported
Status, ROMBIOS (qemu-xen-traditional): Supported
OVMF firmware implements the UEFI boot protocol.
Status, qemu-xen: Supported
Guest creation from the hypervisor at boot without Dom0 intervention.
Status, ARM: Supported
Memory of dom0less DomUs is not scrubbed at boot when bootscrub=on or bootscrub=off are passed as Xen command line parameters. (Memory should be scrubbed with bootscrub=idle.) No XSAs will be issues due to unscrubbed memory.
Allow to setup the static event channel on dom0less system, enabling domains to send/receive notifications.
Status, ARM: Tech Preview
This file contains prose, and machine-readable fragments. The data in a machine-readable fragment relate to the section and subsection in which it is found.
The file is in markdown format. The machine-readable fragments are markdown literals containing RFC-822-like (deb822-like) data.
In each case, descriptions which expand on the name of a feature as provided in the section heading, precede the Status indications. Any paragraphs which follow the Status indication are caveats or qualifications of the information provided in Status fields.
This gives the overall status of the feature, including security support status, functional completeness, etc. Refer to the detailed definitions below.
If support differs based on implementation (for instance, x86 / ARM, Linux / QEMU / FreeBSD), one line for each set of implementations will be listed.
Each Status value corresponds to levels of security support, testing, stability, etc., as follows:
Functional completeness: No
Functional stability: Here be dragons
Interface stability: Not stable
Security supported: No
Functional completeness: Yes
Functional stability: Quirky
Interface stability: Provisionally stable
Security supported: No
Functional completeness: Yes
Functional stability: Normal
Interface stability: Yes
Security supported: Yes
Functional completeness: Yes
Functional stability: Quirky
Interface stability: No (as in, may disappear the next release)
Security supported: Yes
All of these may appear in modified form. There are several interfaces, for instance, which are officially declared as not stable; in such a case this feature may be described as "Stable / Interface not stable".
Does it behave like a fully functional feature? Does it work on all expected platforms, or does it only work for a very specific sub-case? Does it have a sensible UI, or do you have to have a deep understanding of the internals to get it to work properly?
What is the risk of it exhibiting bugs?
General answers to the above:
-
Here be dragons
Pretty likely to still crash / fail to work. Not recommended unless you like life on the bleeding edge.
-
Quirky
Mostly works but may have odd behavior here and there. Recommended for playing around or for non-production use cases.
-
Normal
Ready for production use
If I build a system based on the current interfaces, will they still work when I upgrade to the next version?
-
Not stable
Interface is still in the early stages and still fairly likely to be broken in future updates.
-
Provisionally stable
We're not yet promising backwards compatibility, but we think this is probably the final form of the interface. It may still require some tweaks.
-
Stable
We will try very hard to avoid breaking backwards compatibility, and to fix any regressions that are reported.
Will XSAs be issued if security-related bugs are discovered in the functionality?
If "no", anyone who finds a security-related bug in the feature will be advised to post it publicly to the Xen Project mailing lists (or contact another security response team, if a relevant one exists).
Bugs found after the end of Security-Support-Until in the Release Support section will receive an XSA if they also affect newer, security-supported, versions of Xen. However, the Xen Project will not provide official fixes for non-security-supported versions.
Three common 'diversions' from the 'Supported' category are given the following labels:
-
Supported, Not security supported
Functionally complete, normal stability, interface stable, but no security support
-
Supported, Security support external
This feature is security supported by a different organization (not the XenProject). The extent of support is defined by that organization. It might be limited, e.g. like described in Supported, with caveats below. See External security support below.
-
Supported, with caveats
This feature is security supported only under certain conditions, or support is given only for certain aspects of the feature, or the feature should be used with care because it is easy to use insecurely without knowing it. Additional details will be given in the description.
Not all features interact well with all other features. Some features are only for HVM guests; some don't work with migration, &c.
The XenProject security team provides security support for XenProject projects.
We also provide security support for Xen-related code in Linux, which is an external project but doesn't have its own security process.
External projects that provide their own security support for Xen-related features are listed below.