Merge remote-tracking branch 'remotes/berrange/tags/qcrypto-next-pull-request' into staging

# gpg: Signature made Fri 06 Apr 2018 14:29:10 BST
# gpg:                using RSA key BE86EBB415104FDF
# gpg: Good signature from "Daniel P. Berrange <dan@berrange.com>"
# gpg:                 aka "Daniel P. Berrange <berrange@redhat.com>"
# Primary key fingerprint: DAF3 A6FD B26B 6291 2D0E  8E3F BE86 EBB4 1510 4FDF

* remotes/berrange/tags/qcrypto-next-pull-request:
  crypto: ensure we use a predictable TLS priority setting
  docs: Document -object tls-creds-x509 priority=xxx
  docs: update information for TLS certificate management
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

qemu-doc.texi

@@ -140,6 +140,7 @@ accelerator is required to use more than one host CPU for emulation.
 * direct_linux_boot::  Direct Linux Boot
 * pcsys_usb::          USB emulation
 * vnc_security::       VNC security
+* network_tls::        TLS setup for network services
 * gdb_usage::          GDB usage
 * pcsys_os_specific::  Target OS specific information
 @end menu
@@ -1041,7 +1042,6 @@ considerations depending on the deployment scenarios.
 * vnc_sec_certificate_pw::
 * vnc_sec_sasl::
 * vnc_sec_certificate_sasl::
-* vnc_generate_cert::
 * vnc_setup_sasl::
 @end menu
 @node vnc_sec_none
@@ -1161,25 +1161,105 @@ with the aforementioned TLS + x509 options:
 qemu-system-i386 [...OPTIONS...] -vnc :1,tls,x509,sasl -monitor stdio
 @end example
 
+@node vnc_setup_sasl
 
-@node vnc_generate_cert
-@subsection Generating certificates for VNC
+@subsection Configuring SASL mechanisms
 
-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 necessary 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}.
+The following documentation assumes use of the Cyrus SASL implementation on a
+Linux host, but the principles should apply to any other SASL implementation
+or host. When SASL is enabled, the mechanism configuration will be loaded from
+system default SASL service config /etc/sasl2/qemu.conf. If running QEMU as an
+unprivileged user, an environment variable SASL_CONF_PATH can be used to make
+it search alternate locations for the service config file.
+
+If the TLS option is enabled for VNC, then it will provide session encryption,
+otherwise the SASL mechanism will have to provide encryption. In the latter
+case the list of possible plugins that can be used is drastically reduced. In
+fact only the GSSAPI SASL mechanism provides an acceptable level of security
+by modern standards. Previous versions of QEMU referred to the DIGEST-MD5
+mechanism, however, it has multiple serious flaws described in detail in
+RFC 6331 and thus should never be used any more. The SCRAM-SHA-1 mechanism
+provides a simple username/password auth facility similar to DIGEST-MD5, but
+does not support session encryption, so can only be used in combination with
+TLS.
+
+When not using TLS the recommended configuration is
+
+@example
+mech_list: gssapi
+keytab: /etc/qemu/krb5.tab
+@end example
+
+This says to use the 'GSSAPI' mechanism with the Kerberos v5 protocol, with
+the server principal stored in /etc/qemu/krb5.tab. For this to work the
+administrator of your KDC must generate a Kerberos principal for the server,
+with a name of 'qemu/somehost.example.com@@EXAMPLE.COM' replacing
+'somehost.example.com' with the fully qualified host name of the machine
+running QEMU, and 'EXAMPLE.COM' with the Kerberos Realm.
+
+When using TLS, if username+password authentication is desired, then a
+reasonable configuration is
+
+@example
+mech_list: scram-sha-1
+sasldb_path: /etc/qemu/passwd.db
+@end example
+
+The @code{saslpasswd2} program can be used to populate the @code{passwd.db}
+file with accounts.
+
+Other SASL configurations will be left as an exercise for the reader. Note that
+all mechanisms, except GSSAPI, should be combined with use of TLS to ensure a
+secure data channel.
+
+
+@node network_tls
+@section TLS setup for network services
+
+Almost all network services in QEMU have the ability to use TLS for
+session data encryption, along with x509 certificates for simple
+client authentication. What follows is a description of how to
+generate certificates suitable for usage with QEMU, and applies to
+the VNC server, character devices with the TCP backend, NBD server
+and client, and migration server and client.
+
+At a high level, QEMU requires certificates and private keys to be
+provided in PEM format. Aside from the core fields, the certificates
+should include various extension data sets, including v3 basic
+constraints data, key purpose, key usage and subject alt name.
+
+The GnuTLS package includes a command called @code{certtool} which can
+be used to easily generate certificates and keys in the required format
+with expected data present. Alternatively a certificate management
+service may be used.
+
+At a minimum it is necessary to setup a certificate authority, and
+issue certificates to each server. If using x509 certificates for
+authentication, then each client will also need to be issued a
+certificate.
+
+Assuming that the QEMU network services will only ever be exposed to
+clients on a private intranet, there is no need to use a commercial
+certificate authority to create certificates. A self-signed CA is
+sufficient, and in fact likely to be more secure since it removes
+the ability of malicious 3rd parties to trick the CA into mis-issuing
+certs for impersonating your services. The only likely exception
+where a commercial CA might be desirable is if enabling the VNC
+websockets server and exposing it directly to remote browser clients.
+In such a case it might be useful to use a commercial CA to avoid
+needing to install custom CA certs in the web browsers.
+
+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::
+* tls_generate_ca::
+* tls_generate_server::
+* tls_generate_client::
+* tls_creds_setup::
 @end menu
-@node vnc_generate_ca
-@subsubsection Setup the Certificate Authority
+@node tls_generate_ca
+@subsection 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
@@ -1190,11 +1270,10 @@ issued with it is lost.
 # 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.
-
+To generate a self-signed certificate requires one core piece of information,
+the name of the organization. A template file @code{ca.info} should be
+populated with the desired data to avoid having to deal with interactive
+prompts from certtool:
 @example
 # cat > ca.info <<EOF
 cn = Name of your organization
@@ -1207,123 +1286,224 @@ EOF
            --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.
+The @code{ca} keyword in the template sets the v3 basic constraints extension
+to indicate this certificate is for a CA, while @code{cert_signing_key} sets
+the key usage extension to indicate this will be used for signing other keys.
+The generated @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 anywhere except the host responsible for issuing
+certificates.
 
-@node vnc_generate_server
-@subsubsection Issuing server certificates
+@node tls_generate_server
+@subsection 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
+The core pieces of information for a server certificate are the hostnames and/or IP
+addresses that will be used by clients when connecting. The hostname / IP address
+that the client specifies when connecting will be validated against the hostname(s)
+and IP address(es) recorded in the server certificate, and if no match is found
+the client will close the connection.
+
+Thus it is recommended that the server certificate include both the fully qualified
+and unqualified hostnames. If the server will have permanently assigned IP address(es),
+and clients are likely to use them when connecting, they may also be included in the
+certificate. Both IPv4 and IPv6 addresses are supported. Historically certificates
+only included 1 hostname in the @code{CN} field, however, usage of this field for
+validation is now deprecated. Instead modern TLS clients will validate against the
+Subject Alt Name extension data, which allows for multiple entries. In the future
+usage of the @code{CN} field may be discontinued entirely, so providing SAN
+extension data is strongly recommended.
+
+On the host holding the CA, create template files containing the information
+for each server, and use it to issue server certificates.
+
+@example
+# cat > server-hostNNN.info <<EOF
 organization = Name  of your organization
-cn = server.foo.example.com
+cn = hostNNN.foo.example.com
+dns_name = hostNNN
+dns_name = hostNNN.foo.example.com
+ip_address = 10.0.1.87
+ip_address = 192.8.0.92
+ip_address = 2620:0:cafe::87
+ip_address = 2001:24::92
 tls_www_server
 encryption_key
 signing_key
 EOF
-# certtool --generate-privkey > server-key.pem
+# certtool --generate-privkey > server-hostNNN-key.pem
 # certtool --generate-certificate \
            --load-ca-certificate ca-cert.pem \
            --load-ca-privkey ca-key.pem \
-           --load-privkey server-key.pem \
-           --template server.info \
-           --outfile server-cert.pem
+           --load-privkey server-hostNNN-key.pem \
+           --template server-hostNNN.info \
+           --outfile server-hostNNN-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.
+The @code{dns_name} and @code{ip_address} fields in the template are setting
+the subject alt name extension data. The @code{tls_www_server} keyword is the
+key purpose extension to indicate this certificate is intended for usage in
+a web server. Although QEMU network services are not in fact HTTP servers
+(except for VNC websockets), setting this key purpose is still recommended.
+The @code{encryption_key} and @code{signing_key} keyword is the key usage
+extension to indicate this certificate is intended for usage in the data
+session.
 
-@node vnc_generate_client
-@subsubsection Issuing client certificates
+The @code{server-hostNNN-key.pem} and @code{server-hostNNN-cert.pem} files
+should now be securely copied to the server for which they were generated,
+and renamed to @code{server-key.pem} and @code{server-cert.pem} when added
+to the @code{/etc/pki/qemu} directory on the target host. The @code{server-key.pem}
+file is security sensitive and should be kept protected with file mode 0600
+to prevent disclosure.
+
+@node tls_generate_client
+@subsection Issuing client certificates
+
+The QEMU x509 TLS credential setup defaults to enabling client verification
+using certificates, providing a simple authentication mechanism. If this
+default is used, each client also needs to be issued a certificate. The client
+certificate contains enough metadata to uniquely identify the client with the
+scope of the certificate authority. The client certificate would typically
+include fields for organization, state, city, building, etc.
+
+Once again on the host holding the CA, create template files containing the
+information for each client, and use it to issue 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
+# cat > client-hostNNN.info <<EOF
 country = GB
 state = London
-locality = London
+locality = City Of London
 organization = Name of your organization
-cn = client.foo.example.com
+cn = hostNNN.foo.example.com
 tls_www_client
 encryption_key
 signing_key
 EOF
-# certtool --generate-privkey > client-key.pem
+# certtool --generate-privkey > client-hostNNN-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
+           --load-privkey client-hostNNN-key.pem \
+           --template client-hostNNN.info \
+           --outfile client-hostNNN-cert.pem
+@end example
+
+The subject alt name extension data is not required for clients, so the
+the @code{dns_name} and @code{ip_address} fields are not included.
+The @code{tls_www_client} keyword is the key purpose extension to indicate
+this certificate is intended for usage in a web client. Although QEMU
+network clients are not in fact HTTP clients, setting this key purpose is
+still recommended. The @code{encryption_key} and @code{signing_key} keyword
+is the key usage extension to indicate this certificate is intended for
+usage in the data session.
+
+The @code{client-hostNNN-key.pem} and @code{client-hostNNN-cert.pem} files
+should now be securely copied to the client for which they were generated,
+and renamed to @code{client-key.pem} and @code{client-cert.pem} when added
+to the @code{/etc/pki/qemu} directory on the target host. The @code{client-key.pem}
+file is security sensitive and should be kept protected with file mode 0600
+to prevent disclosure.
+
+If a single host is going to be using TLS in both a client and server
+role, it is possible to create a single certificate to cover both roles.
+This would be quite common for the migration and NBD services, where a
+QEMU process will be started by accepting a TLS protected incoming migration,
+and later itself be migrated out to another host. To generate a single
+certificate, simply include the template data from both the client and server
+instructions in one.
+
+@example
+# cat > both-hostNNN.info <<EOF
+country = GB
+state = London
+locality = City Of London
+organization = Name of your organization
+cn = hostNNN.foo.example.com
+dns_name = hostNNN
+dns_name = hostNNN.foo.example.com
+ip_address = 10.0.1.87
+ip_address = 192.8.0.92
+ip_address = 2620:0:cafe::87
+ip_address = 2001:24::92
+tls_www_server
+tls_www_client
+encryption_key
+signing_key
+EOF
+# certtool --generate-privkey > both-hostNNN-key.pem
+# certtool --generate-certificate \
+           --load-ca-certificate ca-cert.pem \
+           --load-ca-privkey ca-key.pem \
+           --load-privkey both-hostNNN-key.pem \
+           --template both-hostNNN.info \
+           --outfile both-hostNNN-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.
+When copying the PEM files to the target host, save them twice,
+once as @code{server-cert.pem} and @code{server-key.pem}, and
+again as @code{client-cert.pem} and @code{client-key.pem}.
 
+@node tls_creds_setup
+@subsection TLS x509 credential configuration
 
-@node vnc_setup_sasl
+QEMU has a standard mechanism for loading x509 credentials that will be
+used for network services and clients. It requires specifying the
+@code{tls-creds-x509} class name to the @code{--object} command line
+argument for the system emulators.  Each set of credentials loaded should
+be given a unique string identifier via the @code{id} parameter. A single
+set of TLS credentials can be used for multiple network backends, so VNC,
+migration, NBD, character devices can all share the same credentials. Note,
+however, that credentials for use in a client endpoint must be loaded
+separately from those used in a server endpoint.
 
-@subsection Configuring SASL mechanisms
+When specifying the object, the @code{dir} parameters specifies which
+directory contains the credential files. This directory is expected to
+contain files with the names mentioned previously, @code{ca-cert.pem},
+@code{server-key.pem}, @code{server-cert.pem}, @code{client-key.pem}
+and @code{client-cert.pem} as appropriate. It is also possible to
+include a set of pre-generated Diffie-Hellman (DH) parameters in a file
+@code{dh-params.pem}, which can be created using the
+@code{certtool --generate-dh-params} command. If omitted, QEMU will
+dynamically generate DH parameters when loading the credentials.
 
-The following documentation assumes use of the Cyrus SASL implementation on a
-Linux host, but the principals should apply to any other SASL impl. When SASL
-is enabled, the mechanism configuration will be loaded from system default
-SASL service config /etc/sasl2/qemu.conf. If running QEMU as an
-unprivileged user, an environment variable SASL_CONF_PATH can be used
-to make it search alternate locations for the service config.
+The @code{endpoint} parameter indicates whether the credentials will
+be used for a network client or server, and determines which PEM
+files are loaded.
 
-If the TLS option is enabled for VNC, then it will provide session encryption,
-otherwise the SASL mechanism will have to provide encryption. In the latter
-case the list of possible plugins that can be used is drastically reduced. In
-fact only the GSSAPI SASL mechanism provides an acceptable level of security
-by modern standards. Previous versions of QEMU referred to the DIGEST-MD5
-mechanism, however, it has multiple serious flaws described in detail in
-RFC 6331 and thus should never be used any more. The SCRAM-SHA-1 mechanism
-provides a simple username/password auth facility similar to DIGEST-MD5, but
-does not support session encryption, so can only be used in combination with
-TLS.
+The @code{verify} parameter determines whether x509 certificate
+validation should be performed. This defaults to enabled, meaning
+clients will always validate the server hostname against the
+certificate subject alt name fields and/or CN field. It also
+means that servers will request that clients provide a certificate
+and validate them. Verification should never be turned off for
+client endpoints, however, it may be turned off for server endpoints
+if an alternative mechanism is used to authenticate clients. For
+example, the VNC server can use SASL to authenticate clients
+instead.
 
-When not using TLS the recommended configuration is
+To load server credentials with client certificate validation
+enabled
 
 @example
-mech_list: gssapi
-keytab: /etc/qemu/krb5.tab
+$QEMU -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server
 @end example
 
-This says to use the 'GSSAPI' mechanism with the Kerberos v5 protocol, with
-the server principal stored in /etc/qemu/krb5.tab. For this to work the
-administrator of your KDC must generate a Kerberos principal for the server,
-with a name of 'qemu/somehost.example.com@@EXAMPLE.COM' replacing
-'somehost.example.com' with the fully qualified host name of the machine
-running QEMU, and 'EXAMPLE.COM' with the Kerberos Realm.
-
-When using TLS, if username+password authentication is desired, then a
-reasonable configuration is
+while to load client credentials use
 
 @example
-mech_list: scram-sha-1
-sasldb_path: /etc/qemu/passwd.db
+$QEMU -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=client
 @end example
 
-The saslpasswd2 program can be used to populate the passwd.db file with
-accounts.
+Network services which support TLS will all have a @code{tls-creds}
+parameter which expects the ID of the TLS credentials object. For
+example with VNC:
 
-Other SASL configurations will be left as an exercise for the reader. Note that
-all mechanisms except GSSAPI, should be combined with use of TLS to ensure a
-secure data channel.
+@example
+$QEMU -vnc 0.0.0.0:0,tls-creds=tls0
+@end example
 
 @node gdb_usage
 @section GDB usage

qemu-options.hx

@@ -4112,7 +4112,7 @@ expensive operation that consumes random pool entropy, so it is
 recommended that a persistent set of parameters be generated
 upfront and saved.
 
-@item -object tls-creds-x509,id=@var{id},endpoint=@var{endpoint},dir=@var{/path/to/cred/dir},verify-peer=@var{on|off},passwordid=@var{id}
+@item -object tls-creds-x509,id=@var{id},endpoint=@var{endpoint},dir=@var{/path/to/cred/dir},priority=@var{priority},verify-peer=@var{on|off},passwordid=@var{id}
 
 Creates a TLS anonymous credentials object, which can be used to provide
 TLS support on network backends. The @option{id} parameter is a unique
@@ -4145,6 +4145,15 @@ version by providing the @var{passwordid} parameter. This provides
 the ID of a previously created @code{secret} object containing the
 password for decryption.
 
+The @var{priority} parameter allows to override the global default
+priority used by gnutls. This can be useful if the system administrator
+needs to use a weaker set of crypto priorities for QEMU without
+potentially forcing the weakness onto all applications. Or conversely
+if one wants wants a stronger default for QEMU than for all other
+applications, they can do this through this parameter. Its format is
+a gnutls priority string as described at
+@url{https://gnutls.org/manual/html_node/Priority-Strings.html}.
+
 @item -object filter-buffer,id=@var{id},netdev=@var{netdevid},interval=@var{t}[,queue=@var{all|rx|tx}][,status=@var{on|off}]
 
 Interval @var{t} can't be 0, this filter batches the packet delivery: all

tests/test-crypto-tlssession.c

@@ -75,6 +75,7 @@ static QCryptoTLSCreds *test_tls_creds_create(QCryptoTLSCredsEndpoint endpoint,
                      "server" : "client"),
         "dir", certdir,
         "verify-peer", "yes",
+        "priority", "NORMAL",
         /* We skip initial sanity checks here because we
          * want to make sure that problems are being
          * detected at the TLS session validation stage,

tests/test-io-channel-tls.c

@@ -78,6 +78,7 @@ static QCryptoTLSCreds *test_tls_creds_create(QCryptoTLSCredsEndpoint endpoint,
                      "server" : "client"),
         "dir", certdir,
         "verify-peer", "yes",
+        "priority", "NORMAL",
         /* We skip initial sanity checks here because we
          * want to make sure that problems are being
          * detected at the TLS session validation stage,