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

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).

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

Example of use to dump the cipher suites:

  $ qemu-system-x86_64 -S \
    -object tls-cipher-suites,id=mysuite,priority=@SYSTEM \
    -trace qcrypto\*
  1590664444.197123:qcrypto_tls_cipher_suite_priority priority: @SYSTEM
  1590664444.197219:qcrypto_tls_cipher_suite_info data=[0x13,0x02] version=TLS1.3 name=TLS_AES_256_GCM_SHA384
  1590664444.197228:qcrypto_tls_cipher_suite_info data=[0x13,0x03] version=TLS1.3 name=TLS_CHACHA20_POLY1305_SHA256
  1590664444.197233:qcrypto_tls_cipher_suite_info data=[0x13,0x01] version=TLS1.3 name=TLS_AES_128_GCM_SHA256
  1590664444.197236:qcrypto_tls_cipher_suite_info data=[0x13,0x04] version=TLS1.3 name=TLS_AES_128_CCM_SHA256
  1590664444.197240:qcrypto_tls_cipher_suite_info data=[0xc0,0x30] version=TLS1.2 name=TLS_ECDHE_RSA_AES_256_GCM_SHA384
  1590664444.197245:qcrypto_tls_cipher_suite_info data=[0xcc,0xa8] version=TLS1.2 name=TLS_ECDHE_RSA_CHACHA20_POLY1305
  1590664444.197250:qcrypto_tls_cipher_suite_info data=[0xc0,0x14] version=TLS1.0 name=TLS_ECDHE_RSA_AES_256_CBC_SHA1
  1590664444.197254:qcrypto_tls_cipher_suite_info data=[0xc0,0x2f] version=TLS1.2 name=TLS_ECDHE_RSA_AES_128_GCM_SHA256
  1590664444.197258:qcrypto_tls_cipher_suite_info data=[0xc0,0x13] version=TLS1.0 name=TLS_ECDHE_RSA_AES_128_CBC_SHA1
  1590664444.197261:qcrypto_tls_cipher_suite_info data=[0xc0,0x2c] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_256_GCM_SHA384
  1590664444.197266:qcrypto_tls_cipher_suite_info data=[0xcc,0xa9] version=TLS1.2 name=TLS_ECDHE_ECDSA_CHACHA20_POLY1305
  1590664444.197270:qcrypto_tls_cipher_suite_info data=[0xc0,0xad] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_256_CCM
  1590664444.197274:qcrypto_tls_cipher_suite_info data=[0xc0,0x0a] version=TLS1.0 name=TLS_ECDHE_ECDSA_AES_256_CBC_SHA1
  1590664444.197278:qcrypto_tls_cipher_suite_info data=[0xc0,0x2b] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_128_GCM_SHA256
  1590664444.197283:qcrypto_tls_cipher_suite_info data=[0xc0,0xac] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_128_CCM
  1590664444.197287:qcrypto_tls_cipher_suite_info data=[0xc0,0x09] version=TLS1.0 name=TLS_ECDHE_ECDSA_AES_128_CBC_SHA1
  1590664444.197291:qcrypto_tls_cipher_suite_info data=[0x00,0x9d] version=TLS1.2 name=TLS_RSA_AES_256_GCM_SHA384
  1590664444.197296:qcrypto_tls_cipher_suite_info data=[0xc0,0x9d] version=TLS1.2 name=TLS_RSA_AES_256_CCM
  1590664444.197300:qcrypto_tls_cipher_suite_info data=[0x00,0x35] version=TLS1.0 name=TLS_RSA_AES_256_CBC_SHA1
  1590664444.197304:qcrypto_tls_cipher_suite_info data=[0x00,0x9c] version=TLS1.2 name=TLS_RSA_AES_128_GCM_SHA256
  1590664444.197308:qcrypto_tls_cipher_suite_info data=[0xc0,0x9c] version=TLS1.2 name=TLS_RSA_AES_128_CCM
  1590664444.197312:qcrypto_tls_cipher_suite_info data=[0x00,0x2f] version=TLS1.0 name=TLS_RSA_AES_128_CBC_SHA1
  1590664444.197316:qcrypto_tls_cipher_suite_info data=[0x00,0x9f] version=TLS1.2 name=TLS_DHE_RSA_AES_256_GCM_SHA384
  1590664444.197320:qcrypto_tls_cipher_suite_info data=[0xcc,0xaa] version=TLS1.2 name=TLS_DHE_RSA_CHACHA20_POLY1305
  1590664444.197325:qcrypto_tls_cipher_suite_info data=[0xc0,0x9f] version=TLS1.2 name=TLS_DHE_RSA_AES_256_CCM
  1590664444.197329:qcrypto_tls_cipher_suite_info data=[0x00,0x39] version=TLS1.0 name=TLS_DHE_RSA_AES_256_CBC_SHA1
  1590664444.197333:qcrypto_tls_cipher_suite_info data=[0x00,0x9e] version=TLS1.2 name=TLS_DHE_RSA_AES_128_GCM_SHA256
  1590664444.197337:qcrypto_tls_cipher_suite_info data=[0xc0,0x9e] version=TLS1.2 name=TLS_DHE_RSA_AES_128_CCM
  1590664444.197341:qcrypto_tls_cipher_suite_info data=[0x00,0x33] version=TLS1.0 name=TLS_DHE_RSA_AES_128_CBC_SHA1
  1590664444.197345:qcrypto_tls_cipher_suite_count count: 29

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
v8: addressed Laszlo's comments
- updated trace events format to match other crypto ones
- inserted Daniel/Laszlo commit description
- describe object in qemu-options.hx
---
 include/crypto/tls-cipher-suites.h |  38 +++++++++
 crypto/tls-cipher-suites.c         | 127 +++++++++++++++++++++++++++++
 crypto/Makefile.objs               |   1 +
 crypto/trace-events                |   5 ++
 qemu-options.hx                    |  19 +++++
 5 files changed, 190 insertions(+)
 create mode 100644 include/crypto/tls-cipher-suites.h
 create mode 100644 crypto/tls-cipher-suites.c

diff --git a/include/crypto/tls-cipher-suites.h b/include/crypto/tls-cipher-suites.h
new file mode 100644
index 0000000000..3848393a20
--- /dev/null
+++ b/include/crypto/tls-cipher-suites.h
@@ -0,0 +1,38 @@
+/*
+ * QEMU TLS Cipher Suites Registry (RFC8447)
+ *
+ * Copyright (c) 2019 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)
+
+/*
+ * 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;
+
+typedef struct QCryptoTLSCipherSuites {
+    /* <private> */
+    QCryptoTLSCreds parent_obj;
+
+    /* <public> */
+    IANA_TLS_CIPHER *cipher_list;
+    unsigned cipher_count;
+} QCryptoTLSCipherSuites;
+
+#endif /* QCRYPTO_TLSCIPHERSUITES_H */
diff --git a/crypto/tls-cipher-suites.c b/crypto/tls-cipher-suites.c
new file mode 100644
index 0000000000..f02a041f9a
--- /dev/null
+++ b/crypto/tls-cipher-suites.c
@@ -0,0 +1,127 @@
+/*
+ * QEMU TLS Cipher Suites
+ *
+ * Copyright (c) 2019 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 "qemu/error-report.h"
+#include "crypto/tlscreds.h"
+#include "crypto/tls-cipher-suites.h"
+#include "trace.h"
+
+static void parse_cipher_suites(QCryptoTLSCipherSuites *s,
+                                const char *priority_name, Error **errp)
+{
+    int ret;
+    const char *err;
+    gnutls_priority_t pcache;
+    enum { M_ENUMERATE, M_GENERATE, M_DONE } mode;
+
+    assert(priority_name);
+    trace_qcrypto_tls_cipher_suite_priority(priority_name);
+    ret = gnutls_priority_init(&pcache, priority_name, &err);
+    if (ret < 0) {
+        error_setg(errp, "Syntax error using priority '%s': %s",
+                   priority_name, gnutls_strerror(ret));
+        return;
+    }
+
+    for (mode = M_ENUMERATE; mode < M_DONE; mode++) {
+        size_t i;
+
+        for (i = 0;; i++) {
+            int ret;
+            unsigned idx;
+            const char *name;
+            IANA_TLS_CIPHER cipher;
+            gnutls_protocol_t protocol;
+
+            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;
+            }
+
+            if (mode == M_GENERATE) {
+                const char *version;
+
+                version = gnutls_protocol_get_name(protocol);
+                trace_qcrypto_tls_cipher_suite_info(cipher.data[0],
+                                                    cipher.data[1],
+                                                    version, name);
+                s->cipher_list[s->cipher_count] = cipher;
+            }
+            s->cipher_count++;
+        }
+
+        if (mode == M_ENUMERATE) {
+            if (s->cipher_count == 0) {
+                break;
+            }
+            s->cipher_list = g_new(IANA_TLS_CIPHER, s->cipher_count);
+            s->cipher_count = 0;
+        }
+    }
+    trace_qcrypto_tls_cipher_suite_count(s->cipher_count);
+    gnutls_priority_deinit(pcache);
+}
+
+static void qcrypto_tls_cipher_suites_complete(UserCreatable *uc, Error **errp)
+{
+    QCryptoTLSCreds *s = QCRYPTO_TLS_CREDS(uc);
+
+    if (!s->priority) {
+        error_setg(errp, "'priority' property is not set");
+        return;
+    }
+    parse_cipher_suites(QCRYPTO_TLS_CIPHER_SUITES(s), s->priority, errp);
+}
+
+static void qcrypto_tls_cipher_suites_finalize(Object *obj)
+{
+    QCryptoTLSCipherSuites *s = QCRYPTO_TLS_CIPHER_SUITES(obj);
+
+    g_free(s->cipher_list);
+}
+
+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(QCryptoTLSCipherSuites),
+    .instance_finalize = qcrypto_tls_cipher_suites_finalize,
+    .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);
diff --git a/crypto/Makefile.objs b/crypto/Makefile.objs
index c2a371b0b4..1c1b5e21ff 100644
--- a/crypto/Makefile.objs
+++ b/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
diff --git a/crypto/trace-events b/crypto/trace-events
index 9e594d30e8..798b6067ab 100644
--- a/crypto/trace-events
+++ b/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"
diff --git a/qemu-options.hx b/qemu-options.hx
index 93bde2bbc8..c74366d7cc 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4566,6 +4566,25 @@ 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 backends 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
-- 
2.21.3

On 06/09/20 19:07, Philippe Mathieu-Daudé wrote:
> 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 IANA_TLS_CIPHER objects. The firmware uses the IANA_TLS_CIPHER
> array for configuring guest-side TLS, for example in UEFI HTTPS
> Boot.
> 
> 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).
> 
> [Description from Daniel P. Berrangé, edited by Laszlo Ersek.]
> 
> Example of use to dump the cipher suites:
> 
>   $ qemu-system-x86_64 -S \
>     -object tls-cipher-suites,id=mysuite,priority=@SYSTEM \
>     -trace qcrypto\*
>   1590664444.197123:qcrypto_tls_cipher_suite_priority priority: @SYSTEM
>   1590664444.197219:qcrypto_tls_cipher_suite_info data=[0x13,0x02] version=TLS1.3 name=TLS_AES_256_GCM_SHA384
>   1590664444.197228:qcrypto_tls_cipher_suite_info data=[0x13,0x03] version=TLS1.3 name=TLS_CHACHA20_POLY1305_SHA256
>   1590664444.197233:qcrypto_tls_cipher_suite_info data=[0x13,0x01] version=TLS1.3 name=TLS_AES_128_GCM_SHA256
>   1590664444.197236:qcrypto_tls_cipher_suite_info data=[0x13,0x04] version=TLS1.3 name=TLS_AES_128_CCM_SHA256
>   1590664444.197240:qcrypto_tls_cipher_suite_info data=[0xc0,0x30] version=TLS1.2 name=TLS_ECDHE_RSA_AES_256_GCM_SHA384
>   1590664444.197245:qcrypto_tls_cipher_suite_info data=[0xcc,0xa8] version=TLS1.2 name=TLS_ECDHE_RSA_CHACHA20_POLY1305
>   1590664444.197250:qcrypto_tls_cipher_suite_info data=[0xc0,0x14] version=TLS1.0 name=TLS_ECDHE_RSA_AES_256_CBC_SHA1
>   1590664444.197254:qcrypto_tls_cipher_suite_info data=[0xc0,0x2f] version=TLS1.2 name=TLS_ECDHE_RSA_AES_128_GCM_SHA256
>   1590664444.197258:qcrypto_tls_cipher_suite_info data=[0xc0,0x13] version=TLS1.0 name=TLS_ECDHE_RSA_AES_128_CBC_SHA1
>   1590664444.197261:qcrypto_tls_cipher_suite_info data=[0xc0,0x2c] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_256_GCM_SHA384
>   1590664444.197266:qcrypto_tls_cipher_suite_info data=[0xcc,0xa9] version=TLS1.2 name=TLS_ECDHE_ECDSA_CHACHA20_POLY1305
>   1590664444.197270:qcrypto_tls_cipher_suite_info data=[0xc0,0xad] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_256_CCM
>   1590664444.197274:qcrypto_tls_cipher_suite_info data=[0xc0,0x0a] version=TLS1.0 name=TLS_ECDHE_ECDSA_AES_256_CBC_SHA1
>   1590664444.197278:qcrypto_tls_cipher_suite_info data=[0xc0,0x2b] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_128_GCM_SHA256
>   1590664444.197283:qcrypto_tls_cipher_suite_info data=[0xc0,0xac] version=TLS1.2 name=TLS_ECDHE_ECDSA_AES_128_CCM
>   1590664444.197287:qcrypto_tls_cipher_suite_info data=[0xc0,0x09] version=TLS1.0 name=TLS_ECDHE_ECDSA_AES_128_CBC_SHA1
>   1590664444.197291:qcrypto_tls_cipher_suite_info data=[0x00,0x9d] version=TLS1.2 name=TLS_RSA_AES_256_GCM_SHA384
>   1590664444.197296:qcrypto_tls_cipher_suite_info data=[0xc0,0x9d] version=TLS1.2 name=TLS_RSA_AES_256_CCM
>   1590664444.197300:qcrypto_tls_cipher_suite_info data=[0x00,0x35] version=TLS1.0 name=TLS_RSA_AES_256_CBC_SHA1
>   1590664444.197304:qcrypto_tls_cipher_suite_info data=[0x00,0x9c] version=TLS1.2 name=TLS_RSA_AES_128_GCM_SHA256
>   1590664444.197308:qcrypto_tls_cipher_suite_info data=[0xc0,0x9c] version=TLS1.2 name=TLS_RSA_AES_128_CCM
>   1590664444.197312:qcrypto_tls_cipher_suite_info data=[0x00,0x2f] version=TLS1.0 name=TLS_RSA_AES_128_CBC_SHA1
>   1590664444.197316:qcrypto_tls_cipher_suite_info data=[0x00,0x9f] version=TLS1.2 name=TLS_DHE_RSA_AES_256_GCM_SHA384
>   1590664444.197320:qcrypto_tls_cipher_suite_info data=[0xcc,0xaa] version=TLS1.2 name=TLS_DHE_RSA_CHACHA20_POLY1305
>   1590664444.197325:qcrypto_tls_cipher_suite_info data=[0xc0,0x9f] version=TLS1.2 name=TLS_DHE_RSA_AES_256_CCM
>   1590664444.197329:qcrypto_tls_cipher_suite_info data=[0x00,0x39] version=TLS1.0 name=TLS_DHE_RSA_AES_256_CBC_SHA1
>   1590664444.197333:qcrypto_tls_cipher_suite_info data=[0x00,0x9e] version=TLS1.2 name=TLS_DHE_RSA_AES_128_GCM_SHA256
>   1590664444.197337:qcrypto_tls_cipher_suite_info data=[0xc0,0x9e] version=TLS1.2 name=TLS_DHE_RSA_AES_128_CCM
>   1590664444.197341:qcrypto_tls_cipher_suite_info data=[0x00,0x33] version=TLS1.0 name=TLS_DHE_RSA_AES_128_CBC_SHA1
>   1590664444.197345:qcrypto_tls_cipher_suite_count count: 29
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> v8: addressed Laszlo's comments
> - updated trace events format to match other crypto ones
> - inserted Daniel/Laszlo commit description
> - describe object in qemu-options.hx
> ---
>  include/crypto/tls-cipher-suites.h |  38 +++++++++
>  crypto/tls-cipher-suites.c         | 127 +++++++++++++++++++++++++++++
>  crypto/Makefile.objs               |   1 +
>  crypto/trace-events                |   5 ++
>  qemu-options.hx                    |  19 +++++
>  5 files changed, 190 insertions(+)
>  create mode 100644 include/crypto/tls-cipher-suites.h
>  create mode 100644 crypto/tls-cipher-suites.c
> 
> diff --git a/include/crypto/tls-cipher-suites.h b/include/crypto/tls-cipher-suites.h
> new file mode 100644
> index 0000000000..3848393a20
> --- /dev/null
> +++ b/include/crypto/tls-cipher-suites.h
> @@ -0,0 +1,38 @@
> +/*
> + * QEMU TLS Cipher Suites Registry (RFC8447)
> + *
> + * Copyright (c) 2019 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)
> +
> +/*
> + * 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;
> +
> +typedef struct QCryptoTLSCipherSuites {
> +    /* <private> */
> +    QCryptoTLSCreds parent_obj;
> +
> +    /* <public> */
> +    IANA_TLS_CIPHER *cipher_list;
> +    unsigned cipher_count;
> +} QCryptoTLSCipherSuites;
> +
> +#endif /* QCRYPTO_TLSCIPHERSUITES_H */
> diff --git a/crypto/tls-cipher-suites.c b/crypto/tls-cipher-suites.c
> new file mode 100644
> index 0000000000..f02a041f9a
> --- /dev/null
> +++ b/crypto/tls-cipher-suites.c
> @@ -0,0 +1,127 @@
> +/*
> + * QEMU TLS Cipher Suites
> + *
> + * Copyright (c) 2019 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 "qemu/error-report.h"
> +#include "crypto/tlscreds.h"
> +#include "crypto/tls-cipher-suites.h"
> +#include "trace.h"
> +
> +static void parse_cipher_suites(QCryptoTLSCipherSuites *s,
> +                                const char *priority_name, Error **errp)
> +{
> +    int ret;
> +    const char *err;
> +    gnutls_priority_t pcache;
> +    enum { M_ENUMERATE, M_GENERATE, M_DONE } mode;
> +
> +    assert(priority_name);
> +    trace_qcrypto_tls_cipher_suite_priority(priority_name);
> +    ret = gnutls_priority_init(&pcache, priority_name, &err);
> +    if (ret < 0) {
> +        error_setg(errp, "Syntax error using priority '%s': %s",
> +                   priority_name, gnutls_strerror(ret));
> +        return;
> +    }
> +
> +    for (mode = M_ENUMERATE; mode < M_DONE; mode++) {
> +        size_t i;
> +
> +        for (i = 0;; i++) {
> +            int ret;
> +            unsigned idx;
> +            const char *name;
> +            IANA_TLS_CIPHER cipher;
> +            gnutls_protocol_t protocol;
> +
> +            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;
> +            }
> +
> +            if (mode == M_GENERATE) {
> +                const char *version;
> +
> +                version = gnutls_protocol_get_name(protocol);
> +                trace_qcrypto_tls_cipher_suite_info(cipher.data[0],
> +                                                    cipher.data[1],
> +                                                    version, name);
> +                s->cipher_list[s->cipher_count] = cipher;
> +            }
> +            s->cipher_count++;
> +        }
> +
> +        if (mode == M_ENUMERATE) {
> +            if (s->cipher_count == 0) {
> +                break;
> +            }
> +            s->cipher_list = g_new(IANA_TLS_CIPHER, s->cipher_count);
> +            s->cipher_count = 0;
> +        }
> +    }
> +    trace_qcrypto_tls_cipher_suite_count(s->cipher_count);
> +    gnutls_priority_deinit(pcache);
> +}
> +
> +static void qcrypto_tls_cipher_suites_complete(UserCreatable *uc, Error **errp)
> +{
> +    QCryptoTLSCreds *s = QCRYPTO_TLS_CREDS(uc);
> +
> +    if (!s->priority) {
> +        error_setg(errp, "'priority' property is not set");
> +        return;
> +    }
> +    parse_cipher_suites(QCRYPTO_TLS_CIPHER_SUITES(s), s->priority, errp);
> +}
> +
> +static void qcrypto_tls_cipher_suites_finalize(Object *obj)
> +{
> +    QCryptoTLSCipherSuites *s = QCRYPTO_TLS_CIPHER_SUITES(obj);
> +
> +    g_free(s->cipher_list);
> +}
> +
> +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(QCryptoTLSCipherSuites),
> +    .instance_finalize = qcrypto_tls_cipher_suites_finalize,
> +    .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);
> diff --git a/crypto/Makefile.objs b/crypto/Makefile.objs
> index c2a371b0b4..1c1b5e21ff 100644
> --- a/crypto/Makefile.objs
> +++ b/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
> diff --git a/crypto/trace-events b/crypto/trace-events
> index 9e594d30e8..798b6067ab 100644
> --- a/crypto/trace-events
> +++ b/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"
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 93bde2bbc8..c74366d7cc 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4566,6 +4566,25 @@ 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 backends will use to

(1) I think the word "backends" should be replaced by "frontends".

The "id" property is generally used with backends. And then frontends
refer to backend identifiers with properties that are usually *not*
called "id" (but "bus", "chardev", "drive", "netdev" etc). In this case,
"tls-cipher-suites" is the back-end, and fw_cfg is the front-end.

(If I'm wrong about this, please ignore the above.)

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo

> +        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
>