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Julien Grall
b03074bb47
The list p2m->pages contain all the pages used by the P2M. On large
instance this can be quite large and the time spent to call
d->arch.paging.free_page() will take more than 1ms for a 80GB guest
on a Xen running in nested environment on a c5.metal.
By extrapolation, it would take > 100ms for a 8TB guest (what we
current security support). So add some preemption in p2m_teardown()
and propagate to the callers. Note there are 3 places where
the preemption is not enabled:
- hap_final_teardown()/shadow_final_teardown(): We are
preventing update the P2M once the domain is dying (so
no more pages could be allocated) and most of the P2M pages
will be freed in preemptive manneer when relinquishing the
resources. So this is fine to disable preemption.
- shadow_enable(): This is fine because it will undo the allocation
that may have been made by p2m_alloc_table() (so only the root
page table).
The preemption is arbitrarily checked every 1024 iterations.
We now need to include <xen/event.h> in p2m-basic in order to
import the definition for local_events_need_delivery() used by
general_preempt_check(). Ideally, the inclusion should happen in
xen/sched.h but it opened a can of worms.
Note that with the current approach, Xen doesn't keep track on whether
the alt/nested P2Ms have been cleared. So there are some redundant work.
However, this is not expected to incurr too much overhead (the P2M lock
shouldn't be contended during teardown). So this is optimization is
left outside of the security event.
This is part of CVE-2022-33746 / XSA-410.
Signed-off-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
master commit: 8a2111250b
master date: 2022-10-11 14:24:48 +0200
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https://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 (https://www.xen.org).
This file contains some quick-start instructions to install Xen on
your system. For more information see https://www.xen.org/ and
https://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
https://wiki.xenproject.org and in particular
https://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 32-bit:
- GCC 4.9 or later
- GNU Binutils 2.24 or later
- For ARM 64-bit:
- GCC 5.1 or later
- GNU Binutils 2.24 or later
* Development install of zlib (e.g., zlib-dev)
* Development install of Python 2.6 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)
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)
* pandoc, transfig, pod2{man,html,text} for rendering various pieces of
documentation into alternative formats
* 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
* Development install of libbz2, liblzma, liblzo2, and libzstd for DomU
kernel decompression.
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
https://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
https://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 https://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] https://wiki.xen.org/wiki/XenStore
[1] https://wiki.xen.org/wiki/XenStoreReference
[2] https://wiki.xen.org/wiki/Xenstored
Python Runtime Libraries
========================
Various tools, such as pygrub, have the following runtime dependencies:
* Python 2.6 or later.
URL: http://www.python.org/
Debian: python
Note that the build system expects `python` to be available. If your system
only has `python2` or `python3` but not `python` (as in Linux From Scratch),
you will need to create a symlink for it, or specify PYTHON= when invoking
make, like (note the position of PYTHON= matters):
# make PYTHON=/usr/bin/python3
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.