crypto: Add tls-cipher-suites object

On the host OS, various aspects of TLS operation are configurable.
In particular it is possible for the sysadmin to control the TLS
cipher/protocol algorithms that applications are permitted to use.

* Any given crypto library has a built-in default priority list
  defined by the distro maintainer of the library package (or by
  upstream).

* The "crypto-policies" RPM (or equivalent host OS package)
  provides a config file such as "/etc/crypto-policies/config",
  where the sysadmin can set a high level (library-independent)
  policy.

  The "update-crypto-policies --set" command (or equivalent) is
  used to translate the global policy to individual library
  representations, producing files such as
  "/etc/crypto-policies/back-ends/*.config". The generated files,
  if present, are loaded by the various crypto libraries to
  override their own built-in defaults.

  For example, the GNUTLS library may read
  "/etc/crypto-policies/back-ends/gnutls.config".

* A management application (or the QEMU user) may overide the
  system-wide crypto-policies config via their own config, if
  they need to diverge from the former.

Thus the priority order is "QEMU user config" > "crypto-policies
system config" > "library built-in config".

Introduce the "tls-cipher-suites" object for exposing the ordered
list of permitted TLS cipher suites from the host side to the
guest firmware, via fw_cfg. The list is represented as an array
of bytes.

The priority at which the host-side policy is retrieved is given
by the "priority" property of the new object type. For example,
"priority=@SYSTEM" may be used to refer to
"/etc/crypto-policies/back-ends/gnutls.config" (given that QEMU
uses GNUTLS).

The firmware uses the IANA_TLS_CIPHER array for configuring
guest-side TLS, for example in UEFI HTTPS Boot.

[Description from Daniel P. Berrangé, edited by Laszlo Ersek.]

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200623172726.21040-2-philmd@redhat.com>

crypto/Makefile.objs

@@ -13,6 +13,7 @@ crypto-obj-y += cipher.o
 crypto-obj-$(CONFIG_AF_ALG) += afalg.o
 crypto-obj-$(CONFIG_AF_ALG) += cipher-afalg.o
 crypto-obj-$(CONFIG_AF_ALG) += hash-afalg.o
+crypto-obj-$(CONFIG_GNUTLS) += tls-cipher-suites.o
 crypto-obj-y += tlscreds.o
 crypto-obj-y += tlscredsanon.o
 crypto-obj-y += tlscredspsk.o

crypto/tls-cipher-suites.c

@@ -0,0 +1,115 @@
+/*
+ * QEMU TLS Cipher Suites
+ *
+ * Copyright (c) 2018-2020 Red Hat, Inc.
+ *
+ * Author: Philippe Mathieu-Daudé <philmd@redhat.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qom/object_interfaces.h"
+#include "crypto/tlscreds.h"
+#include "crypto/tls-cipher-suites.h"
+#include "trace.h"
+
+/*
+ * IANA registered TLS ciphers:
+ * https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-4
+ */
+typedef struct {
+    uint8_t data[2];
+} QEMU_PACKED IANA_TLS_CIPHER;
+
+GByteArray *qcrypto_tls_cipher_suites_get_data(QCryptoTLSCipherSuites *obj,
+                                               Error **errp)
+{
+    QCryptoTLSCreds *creds = QCRYPTO_TLS_CREDS(obj);
+    gnutls_priority_t pcache;
+    GByteArray *byte_array;
+    const char *err;
+    size_t i;
+    int ret;
+
+    trace_qcrypto_tls_cipher_suite_priority(creds->priority);
+    ret = gnutls_priority_init(&pcache, creds->priority, &err);
+    if (ret < 0) {
+        error_setg(errp, "Syntax error using priority '%s': %s",
+                   creds->priority, gnutls_strerror(ret));
+        return NULL;
+    }
+
+    byte_array = g_byte_array_new();
+
+    for (i = 0;; i++) {
+        int ret;
+        unsigned idx;
+        const char *name;
+        IANA_TLS_CIPHER cipher;
+        gnutls_protocol_t protocol;
+        const char *version;
+
+        ret = gnutls_priority_get_cipher_suite_index(pcache, i, &idx);
+        if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
+            break;
+        }
+        if (ret == GNUTLS_E_UNKNOWN_CIPHER_SUITE) {
+            continue;
+        }
+
+        name = gnutls_cipher_suite_info(idx, (unsigned char *)&cipher,
+                                        NULL, NULL, NULL, &protocol);
+        if (name == NULL) {
+            continue;
+        }
+
+        version = gnutls_protocol_get_name(protocol);
+        g_byte_array_append(byte_array, cipher.data, 2);
+        trace_qcrypto_tls_cipher_suite_info(cipher.data[0],
+                                            cipher.data[1],
+                                            version, name);
+    }
+    trace_qcrypto_tls_cipher_suite_count(byte_array->len);
+    gnutls_priority_deinit(pcache);
+
+    return byte_array;
+}
+
+static void qcrypto_tls_cipher_suites_complete(UserCreatable *uc,
+                                               Error **errp)
+{
+    QCryptoTLSCreds *creds = QCRYPTO_TLS_CREDS(uc);
+
+    if (!creds->priority) {
+        error_setg(errp, "'priority' property is not set");
+        return;
+    }
+}
+
+static void qcrypto_tls_cipher_suites_class_init(ObjectClass *oc, void *data)
+{
+    UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+
+    ucc->complete = qcrypto_tls_cipher_suites_complete;
+}
+
+static const TypeInfo qcrypto_tls_cipher_suites_info = {
+    .parent = TYPE_QCRYPTO_TLS_CREDS,
+    .name = TYPE_QCRYPTO_TLS_CIPHER_SUITES,
+    .instance_size = sizeof(QCryptoTLSCreds),
+    .class_size = sizeof(QCryptoTLSCredsClass),
+    .class_init = qcrypto_tls_cipher_suites_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_USER_CREATABLE },
+        { }
+    }
+};
+
+static void qcrypto_tls_cipher_suites_register_types(void)
+{
+    type_register_static(&qcrypto_tls_cipher_suites_info);
+}
+
+type_init(qcrypto_tls_cipher_suites_register_types);

crypto/trace-events

@@ -21,3 +21,8 @@ qcrypto_tls_creds_x509_load_cert_list(void *creds, const char *file) "TLS creds
 # tlssession.c
 qcrypto_tls_session_new(void *session, void *creds, const char *hostname, const char *authzid, int endpoint) "TLS session new session=%p creds=%p hostname=%s authzid=%s endpoint=%d"
 qcrypto_tls_session_check_creds(void *session, const char *status) "TLS session check creds session=%p status=%s"
+
+# tls-cipher-suites.c
+qcrypto_tls_cipher_suite_priority(const char *name) "priority: %s"
+qcrypto_tls_cipher_suite_info(uint8_t data0, uint8_t data1, const char *version, const char *name) "data=[0x%02x,0x%02x] version=%s name=%s"
+qcrypto_tls_cipher_suite_count(unsigned count) "count: %u"

include/crypto/tls-cipher-suites.h

@@ -0,0 +1,39 @@
+/*
+ * QEMU TLS Cipher Suites Registry (RFC8447)
+ *
+ * Copyright (c) 2018-2020 Red Hat, Inc.
+ *
+ * Author: Philippe Mathieu-Daudé <philmd@redhat.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef QCRYPTO_TLSCIPHERSUITES_H
+#define QCRYPTO_TLSCIPHERSUITES_H
+
+#include "qom/object.h"
+#include "crypto/tlscreds.h"
+
+#define TYPE_QCRYPTO_TLS_CIPHER_SUITES "tls-cipher-suites"
+#define QCRYPTO_TLS_CIPHER_SUITES(obj) \
+    OBJECT_CHECK(QCryptoTLSCipherSuites, (obj), TYPE_QCRYPTO_TLS_CIPHER_SUITES)
+
+typedef struct QCryptoTLSCipherSuites {
+    /* <private> */
+    QCryptoTLSCreds parent_obj;
+    /* <public> */
+} QCryptoTLSCipherSuites;
+
+/**
+  * qcrypto_tls_cipher_suites_get_data:
+  * @obj: pointer to a TLS cipher suites object
+  * @errp: pointer to a NULL-initialized error object
+  *
+  * Returns: reference to a byte array containing the data.
+  * The caller should release the reference when no longer
+  * required.
+  */
+GByteArray *qcrypto_tls_cipher_suites_get_data(QCryptoTLSCipherSuites *obj,
+                                               Error **errp);
+
+#endif /* QCRYPTO_TLSCIPHERSUITES_H */

qemu-options.hx

@@ -4567,6 +4567,25 @@ SRST
         string as described at
         https://gnutls.org/manual/html_node/Priority-Strings.html.
 
+    ``-object tls-cipher-suites,id=id,priority=priority``
+        Creates a TLS cipher suites object, which can be used to control
+        the TLS cipher/protocol algorithms that applications are permitted
+        to use.
+
+        The ``id`` parameter is a unique ID which frontends will use to
+        access the ordered list of permitted TLS cipher suites from the
+        host.
+
+        The ``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
+        https://gnutls.org/manual/html_node/Priority-Strings.html.
+
     ``-object filter-buffer,id=id,netdev=netdevid,interval=t[,queue=all|rx|tx][,status=on|off][,position=head|tail|id=<id>][,insert=behind|before]``
         Interval t can't be 0, this filter batches the packet delivery:
         all packets arriving in a given interval on netdev netdevid are