[v10,5/5] crypto/tls-cipher-suites: Produce fw_cfg consumable blob
diff mbox series

Message ID 20200623172726.21040-6-philmd@redhat.com
State New
Headers show
Series
  • fw_cfg: Add FW_CFG_DATA_GENERATOR; crypto: Add tls-cipher-suites
Related show

Commit Message

Philippe Mathieu-Daudé June 23, 2020, 5:27 p.m. UTC
Since our format is consumable by the fw_cfg device,
we can implement the FW_CFG_DATA_GENERATOR interface.

Example of use to dump the cipher suites (if tracing enabled):

  $ qemu-system-x86_64 -S \
    -object tls-cipher-suites,id=mysuite1,priority=@SYSTEM \
    -fw_cfg name=etc/path/to/ciphers,gen_id=mysuite1 \
    -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>
---
v10: Removed Laszlo Acked-by due to logical changes
---
 crypto/tls-cipher-suites.c | 11 +++++++++++
 qemu-options.hx            | 18 ++++++++++++++++++
 2 files changed, 29 insertions(+)

Comments

Daniel P. Berrangé June 25, 2020, 11:15 a.m. UTC | #1
On Tue, Jun 23, 2020 at 07:27:26PM +0200, Philippe Mathieu-Daudé wrote:
> Since our format is consumable by the fw_cfg device,
> we can implement the FW_CFG_DATA_GENERATOR interface.
> 
> Example of use to dump the cipher suites (if tracing enabled):
> 
>   $ qemu-system-x86_64 -S \
>     -object tls-cipher-suites,id=mysuite1,priority=@SYSTEM \
>     -fw_cfg name=etc/path/to/ciphers,gen_id=mysuite1 \
>     -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>
> ---
> v10: Removed Laszlo Acked-by due to logical changes
> ---
>  crypto/tls-cipher-suites.c | 11 +++++++++++
>  qemu-options.hx            | 18 ++++++++++++++++++
>  2 files changed, 29 insertions(+)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


Regards,
Daniel
Laszlo Ersek July 2, 2020, 10:58 a.m. UTC | #2
On 06/23/20 19:27, Philippe Mathieu-Daudé wrote:
> Since our format is consumable by the fw_cfg device,
> we can implement the FW_CFG_DATA_GENERATOR interface.
> 
> Example of use to dump the cipher suites (if tracing enabled):
> 
>   $ qemu-system-x86_64 -S \
>     -object tls-cipher-suites,id=mysuite1,priority=@SYSTEM \
>     -fw_cfg name=etc/path/to/ciphers,gen_id=mysuite1 \
>     -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>
> ---
> v10: Removed Laszlo Acked-by due to logical changes
> ---
>  crypto/tls-cipher-suites.c | 11 +++++++++++
>  qemu-options.hx            | 18 ++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/crypto/tls-cipher-suites.c b/crypto/tls-cipher-suites.c
> index 5b403f86c9..b3dba00010 100644
> --- a/crypto/tls-cipher-suites.c
> +++ b/crypto/tls-cipher-suites.c
> @@ -13,6 +13,7 @@
>  #include "qom/object_interfaces.h"
>  #include "crypto/tlscreds.h"
>  #include "crypto/tls-cipher-suites.h"
> +#include "hw/nvram/fw_cfg.h"
>  #include "trace.h"
>  
>  /*
> @@ -88,11 +89,20 @@ static void qcrypto_tls_cipher_suites_complete(UserCreatable *uc,
>      }
>  }
>  
> +static GByteArray *qcrypto_tls_cipher_suites_fw_cfg_gen_data(Object *obj,
> +                                                             Error **errp)
> +{
> +    return qcrypto_tls_cipher_suites_get_data(QCRYPTO_TLS_CIPHER_SUITES(obj),
> +                                              errp);
> +}
> +
>  static void qcrypto_tls_cipher_suites_class_init(ObjectClass *oc, void *data)
>  {
>      UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
> +    FWCfgDataGeneratorClass *fwgc = FW_CFG_DATA_GENERATOR_CLASS(oc);
>  
>      ucc->complete = qcrypto_tls_cipher_suites_complete;
> +    fwgc->get_data = qcrypto_tls_cipher_suites_fw_cfg_gen_data;
>  }
>  
>  static const TypeInfo qcrypto_tls_cipher_suites_info = {
> @@ -103,6 +113,7 @@ static const TypeInfo qcrypto_tls_cipher_suites_info = {
>      .class_init = qcrypto_tls_cipher_suites_class_init,
>      .interfaces = (InterfaceInfo[]) {
>          { TYPE_USER_CREATABLE },
> +        { TYPE_FW_CFG_DATA_GENERATOR_INTERFACE },
>          { }
>      }
>  };
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 4f519f35fd..ce54c7359c 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4585,6 +4585,24 @@ SRST
>          string as described at
>          https://gnutls.org/manual/html_node/Priority-Strings.html.
>  
> +        An example of use of this object is to control UEFI HTTPS Boot.
> +        The tls-cipher-suites object exposes 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.
> +
> +        In the following example, the priority at which the host-side policy
> +        is retrieved is given by the ``priority`` property.
> +        Given that QEMU uses GNUTLS, ``priority=@SYSTEM`` may be used to
> +        refer to /etc/crypto-policies/back-ends/gnutls.config.
> +
> +        .. parsed-literal::
> +
> +             # |qemu_system| \
> +                 -object tls-cipher-suites,id=mysuite0,priority=@SYSTEM \
> +                 -fw_cfg name=etc/edk2/https/ciphers,gen_id=mysuite0
> +
>      ``-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
> 

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

Patch
diff mbox series

diff --git a/crypto/tls-cipher-suites.c b/crypto/tls-cipher-suites.c
index 5b403f86c9..b3dba00010 100644
--- a/crypto/tls-cipher-suites.c
+++ b/crypto/tls-cipher-suites.c
@@ -13,6 +13,7 @@ 
 #include "qom/object_interfaces.h"
 #include "crypto/tlscreds.h"
 #include "crypto/tls-cipher-suites.h"
+#include "hw/nvram/fw_cfg.h"
 #include "trace.h"
 
 /*
@@ -88,11 +89,20 @@  static void qcrypto_tls_cipher_suites_complete(UserCreatable *uc,
     }
 }
 
+static GByteArray *qcrypto_tls_cipher_suites_fw_cfg_gen_data(Object *obj,
+                                                             Error **errp)
+{
+    return qcrypto_tls_cipher_suites_get_data(QCRYPTO_TLS_CIPHER_SUITES(obj),
+                                              errp);
+}
+
 static void qcrypto_tls_cipher_suites_class_init(ObjectClass *oc, void *data)
 {
     UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+    FWCfgDataGeneratorClass *fwgc = FW_CFG_DATA_GENERATOR_CLASS(oc);
 
     ucc->complete = qcrypto_tls_cipher_suites_complete;
+    fwgc->get_data = qcrypto_tls_cipher_suites_fw_cfg_gen_data;
 }
 
 static const TypeInfo qcrypto_tls_cipher_suites_info = {
@@ -103,6 +113,7 @@  static const TypeInfo qcrypto_tls_cipher_suites_info = {
     .class_init = qcrypto_tls_cipher_suites_class_init,
     .interfaces = (InterfaceInfo[]) {
         { TYPE_USER_CREATABLE },
+        { TYPE_FW_CFG_DATA_GENERATOR_INTERFACE },
         { }
     }
 };
diff --git a/qemu-options.hx b/qemu-options.hx
index 4f519f35fd..ce54c7359c 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4585,6 +4585,24 @@  SRST
         string as described at
         https://gnutls.org/manual/html_node/Priority-Strings.html.
 
+        An example of use of this object is to control UEFI HTTPS Boot.
+        The tls-cipher-suites object exposes 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.
+
+        In the following example, the priority at which the host-side policy
+        is retrieved is given by the ``priority`` property.
+        Given that QEMU uses GNUTLS, ``priority=@SYSTEM`` may be used to
+        refer to /etc/crypto-policies/back-ends/gnutls.config.
+
+        .. parsed-literal::
+
+             # |qemu_system| \
+                 -object tls-cipher-suites,id=mysuite0,priority=@SYSTEM \
+                 -fw_cfg name=etc/edk2/https/ciphers,gen_id=mysuite0
+
     ``-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