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George Dunlap
6aaa9fb308
The altp2m functionality was originally envisioned to be used in several different configurations, one of which was a single in-guest agent that had full operational control of altp2m. This required the single hypercall to be an HVMOP rather than a DOMCTL, since HVM guests are not allowed to make DOMCTLs. Access to this HVMOP is controlled by a per-domain HVM_PARAM, and defaults to 'off'. Exposing the altp2m functionality to the guest was controversial at the time, but was ultimately accepted. The fact that altp2m is an HVMOP rather than a DOMCTL has caused some problems, however, for those moving forward trying to extend the interface: Extending the interface even for the 'external' use case now means extending an HVMOP, which implicitly extends the surface of attack for the 'internal' use case as well. The result has been that every addition to this interface has also been controversial. Settle the controversy once and for all by documenting 1) the purpose of the altp2m interface, and 2) how to extend it. In particular: * Specify that the fully in-guest agent is a target use case * Specify that all extensions to altp2m functionality should be subops of the HVMOP hypercall * Specify that new subops should be enabled in ALTP2M_mixed mode by default, but that this mode has not been evaluated for safety. Hopefully this will allow the altp2m interface to be developed further without unnecessary controversy. Further discussion: As far as I can tell there are three possible solutions to this controversy. A. Remove the 'internal' functionality as a target by converting the current HVMOP into a DOMCTL. B. Have two hypercalls -- an HVMOP which contains functionality expected to be used by the 'internal' agent, and a DOMCTL for functionality which is expected to be used only be the 'external' agent. C. Agree to add all new subops to the current hypercall (HVMOP), even if we're not sure if they should be exposed to the guest. I think A is a terrible idea. Having a single in-guest agent is a reasonable design choice, and apparently it was even implemented at some point; we should make it straightforward for someone in the future to pick up the work if they want to. I think B is also a bad idea. The people extending it at the moment are primarily concerned with the 'external' use case. There is nobody around to represent whether new functionality should end up in the HVMOP or the DOMCTL, which means that by default it will end up in the DOMCTL. If it is discovered, afterwards, that the new operations *would* be safe and useful for the 'internal' use case, then we will either have to duplicate them inside the HVMOP (which would be terrible) or move the operation from the DOMCTL to the HVMOP (which would make coding an agent against several versions a mess). It just makes more sense to have all the altp2m operations in a single place, and a simple way to control whether they're available to the 'internal' use case or not. As such, I am proposing 'C'. Even within that, we have several options as far as what to do with the current interface: C1: Audit the current subops and make a blacklist of subops not suitable for exposure to the guest. Future subops should be on the blacklist unless they have been evaluated as safe for exposure. C2: Don't blacklist the current subops, but require that all future subops be blacklisted unless they have been evaluated as safe for exposure. C3: Don't blacklist current or future subops for the present; just document that they need to be evaluated (and some potentially blacklisted) before being exposed to a guest in a safety-critical environment. C1 would be ideal, but there's nobody at present to do the work. Given that, C3 has been seen as the best solution in discussion. Reviewed-by: Razvan Cojocaru <rcojocaru@bitdefender.com> Acked-by: Wei Liu <wei.liu2@citrix.com> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
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http://www.xen.org/
What is Xen?
============
Xen is a Virtual Machine Monitor (VMM) originally developed by the
Systems Research Group of the University of Cambridge Computer
Laboratory, as part of the UK-EPSRC funded XenoServers project. Xen
is freely-distributable Open Source software, released under the GNU
GPL. Since its initial public release, Xen has grown a large
development community, spearheaded by xen.org (http://www.xen.org).
This file contains some quick-start instructions to install Xen on
your system. For more information see http:/www.xen.org/ and
http://wiki.xen.org/
Quick-Start Guide
=================
First, this is just a quick-start guide. For more comprehensive
information see the INSTALL file and the Xen wiki at
http://wiki.xenproject.org and in particular
http://wiki.xenproject.org/wiki/Getting_Started.
Second, there are a number of prerequisites for building a Xen source
release. Make sure you have all the following installed, either by
visiting the project webpage or installing a pre-built package
provided by your OS distributor:
* GNU Make v3.80 or later
* C compiler and linker:
- For x86:
- GCC 4.1.2_20070115 or later
- GNU Binutils 2.16.91.0.5 or later
or
- Clang/LLVM 3.5 or later
- For ARM:
- GCC 4.8 or later
- GNU Binutils 2.24 or later
* Development install of zlib (e.g., zlib-dev)
* Development install of Python v2.4 or later (e.g., python-dev)
* Development install of curses (e.g., libncurses-dev)
* Development install of openssl (e.g., openssl-dev)
* Development install of x11 (e.g. xorg-x11-dev)
* Development install of uuid (e.g. uuid-dev)
* Development install of yajl (e.g. libyajl-dev)
* Development install of libaio (e.g. libaio-dev) version 0.3.107 or
greater.
* Development install of GLib v2.0 (e.g. libglib2.0-dev)
* Development install of Pixman (e.g. libpixman-1-dev)
* pkg-config
* bridge-utils package (/sbin/brctl)
* iproute package (/sbin/ip)
* GNU bison and GNU flex
* GNU gettext
* ACPI ASL compiler (iasl)
* Libc multiarch package (e.g. libc6-dev-i386 / glibc-devel.i686).
Required when building on a 64-bit platform to build
32-bit components which are enabled on a default build.
In addition to the above there are a number of optional build
prerequisites. Omitting these will cause the related features to be
disabled at compile time:
* Development install of Ocaml (e.g. ocaml-nox and
ocaml-findlib). Required to build ocaml components which
includes the alternative ocaml xenstored.
* cmake (if building vtpm stub domains)
* markdown
* figlet (for generating the traditional Xen start of day banner)
* systemd daemon development files
* Development install of libnl3 (e.g., libnl-3-200,
libnl-3-dev, etc). Required if network buffering is desired
when using Remus with libxl. See docs/README.remus for detailed
information.
* 16-bit x86 assembler, loader and compiler for qemu-traditional / rombios
(dev86 rpm or bin86 & bcc debs)
* Development install of liblzma for rombios
Second, you need to acquire a suitable kernel for use in domain 0. If
possible you should use a kernel provided by your OS distributor. If
no suitable kernel is available from your OS distributor then refer to
http://wiki.xen.org/wiki/XenDom0Kernels for suggestions for
suitable kernels to use.
If you are looking to compile a Dom0 kernel from source, please refer to
http://wiki.xen.org/wiki/XenParavirtOps.
[NB. Unless noted otherwise, all the following steps should be
performed with root privileges.]
1. Download and untar the source tarball file. This will be a
file named xen-unstable-src.tgz, or xen-$version-src.tgz.
You can also pull the current version from the git or mercurial
repositories at http://xenbits.xen.org/
# tar xzf xen-unstable-src.tgz
Assuming you are using the unstable tree, this will
untar into xen-unstable. The rest of the instructions
use the unstable tree as an example, substitute the
version for unstable.
2. cd to xen-unstable (or whatever you sensibly rename it to).
3. For the very first build, or if you want to destroy build trees,
perform the following steps:
# ./configure
# make world
# make install
See the documentation in the INSTALL file for more info.
This will create and install onto the local machine. It will build
the xen binary (xen.gz), the tools and the documentation.
You can override the destination for make install by setting DESTDIR
to some value.
4. To rebuild an existing tree without modifying the config:
# make dist
This will build and install xen, tools, and docs into the local dist/
directory.
You can override the destination for make install by setting DISTDIR
to some value.
make install and make dist differ in that make install does the
right things for your local machine (installing the appropriate
version of udev scripts, for example), but make dist includes all
versions of those scripts, so that you can copy the dist directory
to another machine and install from that distribution.
xenstore: xenstored and oxenstored
====================================
Xen uses a configuration database called xenstore [0] to maintain configuration
and status information shared between domains. A daemon is implemented as part
of xenstore to act as an interface for access to the database for dom0 and
guests. Two xenstored daemons are supported, one written in C which we refer
to as the xenstored (sometimes referred to as cxenstored), and another written
in Ocaml called oxenstored. Details for xenstore and the different
implementations can be found on the wiki's xenstore reference guide [1] and
the xenstored [2] page. You can choose which xenstore you want to enable as
default on a system through configure:
./configure --with-xenstored=xenstored
./configure --with-xenstored=oxenstored
By default oxenstored will be used if the ocaml development tools are found.
If you enable oxenstored the xenstored will still be built and installed,
the xenstored used can be changed through the configuration file:
/etc/sysconfig/xencommons
or
/etc/default/xencommons
You can change the preferred xenstored you want to use in the configuration
but since we cannot stop the daemon a reboot will be required to make the
change take effect.
[0] http://wiki.xen.org/wiki/XenStore
[1] http://wiki.xen.org/wiki/XenStoreReference
[2] http://wiki.xen.org/wiki/Xenstored
Python Runtime Libraries
========================
Various tools, such as pygrub, have the following runtime dependencies:
* Python 2.3 or later.
URL: http://www.python.org/
Debian: python
Intel(R) Trusted Execution Technology Support
=============================================
Intel's technology for safer computing, Intel(R) Trusted Execution Technology
(Intel(R) TXT), defines platform-level enhancements that provide the building
blocks for creating trusted platforms. For more information, see
http://www.intel.com/technology/security/.
Intel(R) TXT support is provided by the Trusted Boot (tboot) module in
conjunction with minimal logic in the Xen hypervisor.
Tboot is an open source, pre- kernel/VMM module that uses Intel(R) TXT to
perform a measured and verified launch of an OS kernel/VMM.
The Trusted Boot module is available from
http://sourceforge.net/projects/tboot. This project hosts the code in a
mercurial repo at http://tboot.sourceforge.net/hg/tboot.hg and contains
tarballs of the source. Instructions in the tboot README describe how
to modify grub.conf to use tboot to launch Xen.
There are optional targets as part of Xen's top-level makefile that will
download and build tboot: install-tboot, build-tboot, dist-tboot, clean-tboot.
These will download the latest tar file from the SourceForge site using wget,
then build/install/dist according to Xen's settings.