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Document all VNC authentication options, by Daniel P. Berrange.

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git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@3140 c046a42c-6fe2-441c-8c8c-71466251a162
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ths 2007-08-25 01:40:37 +00:00
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qemu-doc.texi
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@ -129,6 +129,7 @@ Download the experimental binary installer at
* pcsys_network:: Network emulation * pcsys_network:: Network emulation
* direct_linux_boot:: Direct Linux Boot * direct_linux_boot:: Direct Linux Boot
* pcsys_usb:: USB emulation * pcsys_usb:: USB emulation
* vnc_security:: VNC security
* gdb_usage:: GDB usage * gdb_usage:: GDB usage
* pcsys_os_specific:: Target OS specific information * pcsys_os_specific:: Target OS specific information
@end menu @end menu
@ -243,53 +244,6 @@ Set virtual RAM size to @var{megs} megabytes. Default is 128 MB.
Simulate an SMP system with @var{n} CPUs. On the PC target, up to 255 Simulate an SMP system with @var{n} CPUs. On the PC target, up to 255
CPUs are supported. CPUs are supported.
@item -nographic
Normally, QEMU uses SDL to display the VGA output. With this option,
you can totally disable graphical output so that QEMU is a simple
command line application. The emulated serial port is redirected on
the console. Therefore, you can still use QEMU to debug a Linux kernel
with a serial console.
@item -no-frame
Do not use decorations for SDL windows and start them using the whole
available screen space. This makes the using QEMU in a dedicated desktop
workspace more convenient.
@item -vnc display
Normally, QEMU uses SDL to display the VGA output. With this option,
you can have QEMU listen on VNC display @var{display} and redirect the VGA
display over the VNC session. It is very useful to enable the usb
tablet device when using this option (option @option{-usbdevice
tablet}). When using the VNC display, you must use the @option{-k}
option to set the keyboard layout if you are not using en-us.
@var{display} may be in the form @var{interface:d}, in which case connections
will only be allowed from @var{interface} on display @var{d}. Optionally,
@var{interface} can be omitted. @var{display} can also be in the form
@var{unix:path} where @var{path} is the location of a unix socket to listen for
connections on.
@item -k language
Use keyboard layout @var{language} (for example @code{fr} for
French). This option is only needed where it is not easy to get raw PC
keycodes (e.g. on Macs, with some X11 servers or with a VNC
display). You don't normally need to use it on PC/Linux or PC/Windows
hosts.
The available layouts are:
@example
ar de-ch es fo fr-ca hu ja mk no pt-br sv
da en-gb et fr fr-ch is lt nl pl ru th
de en-us fi fr-be hr it lv nl-be pt sl tr
@end example
The default is @code{en-us}.
@item -audio-help @item -audio-help
Will show the audio subsystem help: list of drivers, tunable Will show the audio subsystem help: list of drivers, tunable
@ -312,9 +266,6 @@ Set the real time clock to local time (the default is to UTC
time). This option is needed to have correct date in MS-DOS or time). This option is needed to have correct date in MS-DOS or
Windows. Windows.
@item -full-screen
Start in full screen.
@item -pidfile file @item -pidfile file
Store the QEMU process PID in @var{file}. It is useful if you launch QEMU Store the QEMU process PID in @var{file}. It is useful if you launch QEMU
from a script. from a script.
@ -340,6 +291,117 @@ caption. The name will also be used for the VNC server.
@end table @end table
Display options:
@table @option
@item -nographic
Normally, QEMU uses SDL to display the VGA output. With this option,
you can totally disable graphical output so that QEMU is a simple
command line application. The emulated serial port is redirected on
the console. Therefore, you can still use QEMU to debug a Linux kernel
with a serial console.
@item -no-frame
Do not use decorations for SDL windows and start them using the whole
available screen space. This makes the using QEMU in a dedicated desktop
workspace more convenient.
@item -full-screen
Start in full screen.
@item -vnc display[,option[,option[,...]]]
Normally, QEMU uses SDL to display the VGA output. With this option,
you can have QEMU listen on VNC display @var{display} and redirect the VGA
display over the VNC session. It is very useful to enable the usb
tablet device when using this option (option @option{-usbdevice
tablet}). When using the VNC display, you must use the @option{-k}
parameter to set the keyboard layout if you are not using en-us. Valid
syntax for the @var{display} is
@table @code
@item @var{interface:d}
TCP connections will only be allowed from @var{interface} on display @var{d}.
By convention the TCP port is 5900+@var{d}. Optionally, @var{interface} can
be omitted in which case the server will bind to all interfaces.
@item @var{unix:path}
Connections will be allowed over UNIX domain sockets where @var{path} is the
location of a unix socket to listen for connections on.
@item @var{none}
VNC is initialized by not started. The monitor @code{change} command can be used
to later start the VNC server.
@end table
Following the @var{display} value there may be one or more @var{option} flags
separated by commas. Valid options are
@table @code
@item @var{password}
Require that password based authentication is used for client connections.
The password must be set separately using the @code{change} command in the
@ref{pcsys_monitor}
@item @var{tls}
Require that client use TLS when communicating with the VNC server. This
uses anonymous TLS credentials so is susceptible to a man-in-the-middle
attack. It is recommended that this option be combined with either the
@var{x509} or @var{x509verify} options.
@item @var{x509=/path/to/certificate/dir}
Valid if @var{tls} is specified. Require that x509 credentials are used
for negotiating the TLS session. The server will send its x509 certificate
to the client. It is recommended that a password be set on the VNC server
to provide authentication of the client when this is used. The path following
this option specifies where the x509 certificates are to be loaded from.
See the @ref{vnc_security} section for details on generating certificates.
@item @var{x509verify=/path/to/certificate/dir}
Valid if @var{tls} is specified. Require that x509 credentials are used
for negotiating the TLS session. The server will send its x509 certificate
to the client, and request that the client send its own x509 certificate.
The server will validate the client's certificate against the CA certificate,
and reject clients when validation fails. If the certificate authority is
trusted, this is a sufficient authentication mechanism. You may still wish
to set a password on the VNC server as a second authentication layer. The
path following this option specifies where the x509 certificates are to
be loaded from. See the @ref{vnc_security} section for details on generating
certificates.
@end table
@item -k language
Use keyboard layout @var{language} (for example @code{fr} for
French). This option is only needed where it is not easy to get raw PC
keycodes (e.g. on Macs, with some X11 servers or with a VNC
display). You don't normally need to use it on PC/Linux or PC/Windows
hosts.
The available layouts are:
@example
ar de-ch es fo fr-ca hu ja mk no pt-br sv
da en-gb et fr fr-ch is lt nl pl ru th
de en-us fi fr-be hr it lv nl-be pt sl tr
@end example
The default is @code{en-us}.
@end table
USB options: USB options:
@table @option @table @option
@ -862,8 +924,38 @@ Quit the emulator.
@item eject [-f] device @item eject [-f] device
Eject a removable medium (use -f to force it). Eject a removable medium (use -f to force it).
@item change device filename @item change device setting
Change a removable medium.
Change the configuration of a device
@table @option
@item change @var{diskdevice} @var{filename}
Change the medium for a removable disk device to point to @var{filename}. eg
@example
(qemu) change cdrom /path/to/some.iso
@end example
@item change vnc @var{display,options}
Change the configuration of the VNC server. The valid syntax for @var{display}
and @var{options} are described at @ref{sec_invocation}. eg
@example
(qemu) change vnc localhost:1
@end example
@item change vnc password
Change the password associated with the VNC server. The monitor will prompt for
the new password to be entered. VNC passwords are only significant upto 8 letters.
eg.
@example
(qemu) change vnc password
Password: ********
@end example
@end table
@item screendump filename @item screendump filename
Save screen into PPM image @var{filename}. Save screen into PPM image @var{filename}.
@ -1421,6 +1513,213 @@ plugged. You can use the option @option{-usbdevice} to do the same.
When relaunching QEMU, you may have to unplug and plug again the USB When relaunching QEMU, you may have to unplug and plug again the USB
device to make it work again (this is a bug). device to make it work again (this is a bug).
@node vnc_security
@section VNC security
The VNC server capability provides access to the graphical console
of the guest VM across the network. This has a number of security
considerations depending on the deployment scenarios.
@menu
* vnc_sec_none::
* vnc_sec_password::
* vnc_sec_certificate::
* vnc_sec_certificate_verify::
* vnc_sec_certificate_pw::
* vnc_generate_cert::
@end menu
@node vnc_sec_none
@subsection Without passwords
The simplest VNC server setup does not include any form of authentication.
For this setup it is recommended to restrict it to listen on a UNIX domain
socket only. For example
@example
qemu [...OPTIONS...] -vnc unix:/home/joebloggs/.qemu-myvm-vnc
@end example
This ensures that only users on local box with read/write access to that
path can access the VNC server. To securely access the VNC server from a
remote machine, a combination of netcat+ssh can be used to provide a secure
tunnel.
@node vnc_sec_password
@subsection With passwords
The VNC protocol has limited support for password based authentication. Since
the protocol limits passwords to 8 characters it should not be considered
to provide high security. The password can be fairly easily brute-forced by
a client making repeat connections. For this reason, a VNC server using password
authentication should be restricted to only listen on the loopback interface
or UNIX domain sockets. Password ayuthentication is requested with the @code{password}
option, and then once QEMU is running the password is set with the monitor. Until
the monitor is used to set the password all clients will be rejected.
@example
qemu [...OPTIONS...] -vnc :1,password -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)
@end example
@node vnc_sec_certificate
@subsection With x509 certificates
The QEMU VNC server also implements the VeNCrypt extension allowing use of
TLS for encryption of the session, and x509 certificates for authentication.
The use of x509 certificates is strongly recommended, because TLS on its
own is susceptible to man-in-the-middle attacks. Basic x509 certificate
support provides a secure session, but no authentication. This allows any
client to connect, and provides an encrypted session.
@example
qemu [...OPTIONS...] -vnc :1,tls,x509=/etc/pki/qemu -monitor stdio
@end example
In the above example @code{/etc/pki/qemu} should contain at least three files,
@code{ca-cert.pem}, @code{server-cert.pem} and @code{server-key.pem}. Unprivileged
users will want to use a private directory, for example @code{$HOME/.pki/qemu}.
NB the @code{server-key.pem} file should be protected with file mode 0600 to
only be readable by the user owning it.
@node vnc_sec_certificate_verify
@subsection With x509 certificates and client verification
Certificates can also provide a means to authenticate the client connecting.
The server will request that the client provide a certificate, which it will
then validate against the CA certificate. This is a good choice if deploying
in an environment with a private internal certificate authority.
@example
qemu [...OPTIONS...] -vnc :1,tls,x509verify=/etc/pki/qemu -monitor stdio
@end example
@node vnc_sec_certificate_pw
@subsection With x509 certificates, client verification and passwords
Finally, the previous method can be combined with VNC password authentication
to provide two layers of authentication for clients.
@example
qemu [...OPTIONS...] -vnc :1,password,tls,x509verify=/etc/pki/qemu -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)
@end example
@node vnc_generate_cert
@subsection Generating certificates for VNC
The GNU TLS packages provides a command called @code{certtool} which can
be used to generate certificates and keys in PEM format. At a minimum it
is neccessary to setup a certificate authority, and issue certificates to
each server. If using certificates for authentication, then each client
will also need to be issued a certificate. The recommendation is for the
server to keep its certificates in either @code{/etc/pki/qemu} or for
unprivileged users in @code{$HOME/.pki/qemu}.
@menu
* vnc_generate_ca::
* vnc_generate_server::
* vnc_generate_client::
@end menu
@node vnc_generate_ca
@subsubsection Setup the Certificate Authority
This step only needs to be performed once per organization / organizational
unit. First the CA needs a private key. This key must be kept VERY secret
and secure. If this key is compromised the entire trust chain of the certificates
issued with it is lost.
@example
# certtool --generate-privkey > ca-key.pem
@end example
A CA needs to have a public certificate. For simplicity it can be a self-signed
certificate, or one issue by a commercial certificate issuing authority. To
generate a self-signed certificate requires one core piece of information, the
name of the organization.
@example
# cat > ca.info <<EOF
cn = Name of your organization
ca
cert_signing_key
EOF
# certtool --generate-self-signed \
--load-privkey ca-key.pem
--template ca.info \
--outfile ca-cert.pem
@end example
The @code{ca-cert.pem} file should be copied to all servers and clients wishing to utilize
TLS support in the VNC server. The @code{ca-key.pem} must not be disclosed/copied at all.
@node vnc_generate_server
@subsubsection Issuing server certificates
Each server (or host) needs to be issued with a key and certificate. When connecting
the certificate is sent to the client which validates it against the CA certificate.
The core piece of information for a server certificate is the hostname. This should
be the fully qualified hostname that the client will connect with, since the client
will typically also verify the hostname in the certificate. On the host holding the
secure CA private key:
@example
# cat > server.info <<EOF
organization = Name of your organization
cn = server.foo.example.com
tls_www_server
encryption_key
signing_key
EOF
# certtool --generate-privkey > server-key.pem
# certtool --generate-certificate \
--load-ca-certificate ca-cert.pem \
--load-ca-privkey ca-key.pem \
--load-privkey server server-key.pem \
--template server.info \
--outfile server-cert.pem
@end example
The @code{server-key.pem} and @code{server-cert.pem} files should now be securely copied
to the server for which they were generated. The @code{server-key.pem} is security
sensitive and should be kept protected with file mode 0600 to prevent disclosure.
@node vnc_generate_client
@subsubsection Issuing client certificates
If the QEMU VNC server is to use the @code{x509verify} option to validate client
certificates as its authentication mechanism, each client also needs to be issued
a certificate. The client certificate contains enough metadata to uniquely identify
the client, typically organization, state, city, building, etc. On the host holding
the secure CA private key:
@example
# cat > client.info <<EOF
country = GB
state = London
locality = London
organiazation = Name of your organization
cn = client.foo.example.com
tls_www_client
encryption_key
signing_key
EOF
# certtool --generate-privkey > client-key.pem
# certtool --generate-certificate \
--load-ca-certificate ca-cert.pem \
--load-ca-privkey ca-key.pem \
--load-privkey client-key.pem \
--template client.info \
--outfile client-cert.pem
@end example
The @code{client-key.pem} and @code{client-cert.pem} files should now be securely
copied to the client for which they were generated.
@node gdb_usage @node gdb_usage
@section GDB usage @section GDB usage