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| -rw-r--r-- | Makefile | 2 | ||||
| -rw-r--r-- | docs/security.texi | 131 | ||||
| -rw-r--r-- | qemu-doc.texi | 3 |
3 files changed, 135 insertions, 1 deletions
@@ -976,7 +976,7 @@ qemu-doc.html qemu-doc.info qemu-doc.pdf qemu-doc.txt: \ qemu-img.texi qemu-nbd.texi qemu-options.texi qemu-option-trace.texi \ qemu-deprecated.texi qemu-monitor.texi qemu-img-cmds.texi qemu-ga.texi \ qemu-monitor-info.texi docs/qemu-block-drivers.texi \ - docs/qemu-cpu-models.texi + docs/qemu-cpu-models.texi docs/security.texi docs/interop/qemu-ga-ref.dvi docs/interop/qemu-ga-ref.html \ docs/interop/qemu-ga-ref.info docs/interop/qemu-ga-ref.pdf \ diff --git a/docs/security.texi b/docs/security.texi new file mode 100644 index 0000000000..927764f1e6 --- /dev/null +++ b/docs/security.texi @@ -0,0 +1,131 @@ +@node Security +@chapter Security + +@section Overview + +This chapter explains the security requirements that QEMU is designed to meet +and principles for securely deploying QEMU. + +@section Security Requirements + +QEMU supports many different use cases, some of which have stricter security +requirements than others. The community has agreed on the overall security +requirements that users may depend on. These requirements define what is +considered supported from a security perspective. + +@subsection Virtualization Use Case + +The virtualization use case covers cloud and virtual private server (VPS) +hosting, as well as traditional data center and desktop virtualization. These +use cases rely on hardware virtualization extensions to execute guest code +safely on the physical CPU at close-to-native speed. + +The following entities are untrusted, meaning that they may be buggy or +malicious: + +@itemize +@item Guest +@item User-facing interfaces (e.g. VNC, SPICE, WebSocket) +@item Network protocols (e.g. NBD, live migration) +@item User-supplied files (e.g. disk images, kernels, device trees) +@item Passthrough devices (e.g. PCI, USB) +@end itemize + +Bugs affecting these entities are evaluated on whether they can cause damage in +real-world use cases and treated as security bugs if this is the case. + +@subsection Non-virtualization Use Case + +The non-virtualization use case covers emulation using the Tiny Code Generator +(TCG). In principle the TCG and device emulation code used in conjunction with +the non-virtualization use case should meet the same security requirements as +the virtualization use case. However, for historical reasons much of the +non-virtualization use case code was not written with these security +requirements in mind. + +Bugs affecting the non-virtualization use case are not considered security +bugs at this time. Users with non-virtualization use cases must not rely on +QEMU to provide guest isolation or any security guarantees. + +@section Architecture + +This section describes the design principles that ensure the security +requirements are met. + +@subsection Guest Isolation + +Guest isolation is the confinement of guest code to the virtual machine. When +guest code gains control of execution on the host this is called escaping the +virtual machine. Isolation also includes resource limits such as throttling of +CPU, memory, disk, or network. Guests must be unable to exceed their resource +limits. + +QEMU presents an attack surface to the guest in the form of emulated devices. +The guest must not be able to gain control of QEMU. Bugs in emulated devices +could allow malicious guests to gain code execution in QEMU. At this point the +guest has escaped the virtual machine and is able to act in the context of the +QEMU process on the host. + +Guests often interact with other guests and share resources with them. A +malicious guest must not gain control of other guests or access their data. +Disk image files and network traffic must be protected from other guests unless +explicitly shared between them by the user. + +@subsection Principle of Least Privilege + +The principle of least privilege states that each component only has access to +the privileges necessary for its function. In the case of QEMU this means that +each process only has access to resources belonging to the guest. + +The QEMU process should not have access to any resources that are inaccessible +to the guest. This way the guest does not gain anything by escaping into the +QEMU process since it already has access to those same resources from within +the guest. + +Following the principle of least privilege immediately fulfills guest isolation +requirements. For example, guest A only has access to its own disk image file +@code{a.img} and not guest B's disk image file @code{b.img}. + +In reality certain resources are inaccessible to the guest but must be +available to QEMU to perform its function. For example, host system calls are +necessary for QEMU but are not exposed to guests. A guest that escapes into +the QEMU process can then begin invoking host system calls. + +New features must be designed to follow the principle of least privilege. +Should this not be possible for technical reasons, the security risk must be +clearly documented so users are aware of the trade-off of enabling the feature. + +@subsection Isolation mechanisms + +Several isolation mechanisms are available to realize this architecture of +guest isolation and the principle of least privilege. With the exception of +Linux seccomp, these mechanisms are all deployed by management tools that +launch QEMU, such as libvirt. They are also platform-specific so they are only +described briefly for Linux here. + +The fundamental isolation mechanism is that QEMU processes must run as +unprivileged users. Sometimes it seems more convenient to launch QEMU as +root to give it access to host devices (e.g. @code{/dev/net/tun}) but this poses a +huge security risk. File descriptor passing can be used to give an otherwise +unprivileged QEMU process access to host devices without running QEMU as root. +It is also possible to launch QEMU as a non-root user and configure UNIX groups +for access to @code{/dev/kvm}, @code{/dev/net/tun}, and other device nodes. +Some Linux distros already ship with UNIX groups for these devices by default. + +@itemize +@item SELinux and AppArmor make it possible to confine processes beyond the +traditional UNIX process and file permissions model. They restrict the QEMU +process from accessing processes and files on the host system that are not +needed by QEMU. + +@item Resource limits and cgroup controllers provide throughput and utilization +limits on key resources such as CPU time, memory, and I/O bandwidth. + +@item Linux namespaces can be used to make process, file system, and other system +resources unavailable to QEMU. A namespaced QEMU process is restricted to only +those resources that were granted to it. + +@item Linux seccomp is available via the QEMU @option{--sandbox} option. It disables +system calls that are not needed by QEMU, thereby reducing the host kernel +attack surface. +@end itemize diff --git a/qemu-doc.texi b/qemu-doc.texi index ae3c3f9632..577d1e8376 100644 --- a/qemu-doc.texi +++ b/qemu-doc.texi @@ -38,6 +38,7 @@ * QEMU Guest Agent:: * QEMU User space emulator:: * System requirements:: +* Security:: * Implementation notes:: * Deprecated features:: * Supported build platforms:: @@ -2878,6 +2879,8 @@ added with Linux 4.5 which is supported by the major distros. And even if RHEL7 has kernel 3.10, KVM there has the required functionality there to make it close to a 4.5 or newer kernel. +@include docs/security.texi + @include qemu-tech.texi @include qemu-deprecated.texi |