hostnamed: expose DMI board_asset_tag as BoardAssetTag

Exposes /sys/class/dmi/id/board_asset_tag via hostnamed's D-Bus,
Varlink and hostnamectl interfaces, mirroring the ChassisAssetTag
support added in PR systemd#36487.

This is useful for attestation on AWS EC2, where the EC2 instance ID
is exposed as board_asset_tag [1]. The instance ID can then be used
to fetch the instance's Endorsement Key via the EC2 API [2]. 
I am planning to use this in SPIRE's TPM attestation plugin [3].

[1] https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/identify_ec2_instances.html
[2] https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/retrieve-ekpub.html
[3] spiffe/spire-tpm-plugin#35

Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: arianvp

hwdb.d/20-dmi-id.hwdb

@@ -63,6 +63,16 @@ dmi:*:catToBeFilledByO.E.M.:*
 dmi:*:catTo Be Filled By O.E.M.:*
  ID_CHASSIS_ASSET_TAG_IS_RUBBISH=1
 
+dmi:*:ratDefaultstring:*
+dmi:*:ratDefault string:*
+dmi:*:ratN/A:*
+dmi:*:ratO.E.M.:*
+dmi:*:ratOEM:*
+dmi:*:ratTobefilledbyO.E.M.:*
+dmi:*:ratToBeFilledByO.E.M.:*
+dmi:*:ratTo Be Filled By O.E.M.:*
+ ID_BOARD_ASSET_TAG_IS_RUBBISH=1
+
 # Fix "Lenovo" capitalization in /sys/class/dmi/id/sys_vendor
 dmi:bvnLENOVO*
  ID_SYSFS_ATTRIBUTE_MODEL=product_version

man/org.freedesktop.hostname1.xml

@@ -115,6 +115,8 @@ node /org/freedesktop/hostname1 {
       readonly u VSockCID = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly s ChassisAssetTag = '...';
+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+      readonly s BoardAssetTag = '...';
   };
   interface org.freedesktop.DBus.Peer { ... };
   interface org.freedesktop.DBus.Introspectable { ... };
@@ -210,6 +212,8 @@ node /org/freedesktop/hostname1 {
 
     <variablelist class="dbus-property" generated="True" extra-ref="ChassisAssetTag"/>
 
+    <variablelist class="dbus-property" generated="True" extra-ref="BoardAssetTag"/>
+
     <!--End of Autogenerated section-->
 
     <para>Whenever the hostname or other metadata is changed via the daemon,
@@ -342,6 +346,9 @@ node /org/freedesktop/hostname1 {
     <para><varname>ChassisAssetTag</varname> exposes an unique identifier of the system chassis. If this
     information is not known this property is set to an empty string.</para>
 
+    <para><varname>BoardAssetTag</varname> exposes an unique identifier of the system board. If this
+    information is not known this property is set to an empty string.</para>
+
     <refsect2>
       <title>Methods</title>
 
@@ -505,6 +512,7 @@ node /org/freedesktop/hostname1 {
       <varname>OperatingSystemImageVersion</varname>, <varname>HardwareSKU</varname>, and
       <varname>HardwareVersion</varname> were added in version 258.</para>
       <para><varname>OperatingSystemFancyName</varname> was added in version 260.</para>
+      <para><varname>BoardAssetTag</varname> was added in version 261.</para>
       <para><function>GetMachineInfo()</function> was added in version 261.</para>
     </refsect2>
   </refsect1>

rules.d/60-dmi-id.rules

@@ -23,6 +23,10 @@ ENV{ID_HARDWARE_VERSION}=="", ENV{ID_BOARD_VERSION_IS_RUBBISH}!="1", ENV{ID_HARD
 ENV{MODALIAS}!="", ATTR{chassis_asset_tag}!="", IMPORT{builtin}="hwdb '$attr{modalias}cat$attr{chassis_asset_tag}:'"
 ENV{ID_CHASSIS_ASSET_TAG_IS_RUBBISH}!="1", ENV{ID_CHASSIS_ASSET_TAG}="$attr{chassis_asset_tag}"
 
+# Board asset tag
+ENV{MODALIAS}!="", ATTR{board_asset_tag}!="", IMPORT{builtin}="hwdb '$attr{modalias}rat$attr{board_asset_tag}:'"
+ENV{ID_BOARD_ASSET_TAG_IS_RUBBISH}!="1", ENV{ID_BOARD_ASSET_TAG}="$attr{board_asset_tag}"
+
 # Allow units to be ordered after the DMI device
 TAG+="systemd"
 

src/hostname/hostnamectl.c

@@ -47,6 +47,7 @@ typedef struct StatusInfo {
         const char *icon_name;
         const char *chassis;
         const char *chassis_asset_tag;
+        const char *board_asset_tag;
         const char *deployment;
         const char *location;
         const char *kernel_name;
@@ -180,6 +181,14 @@ static int print_status_info(StatusInfo *i) {
                         return table_log_add_error(r);
         }
 
+        if (!isempty(i->board_asset_tag)) {
+                r = table_add_many(table,
+                                   TABLE_FIELD, "Board Asset Tag",
+                                   TABLE_STRING, i->board_asset_tag);
+                if (r < 0)
+                        return table_log_add_error(r);
+        }
+
         if (!isempty(i->deployment)) {
                 r = table_add_many(table,
                                    TABLE_FIELD, "Deployment",
@@ -425,6 +434,7 @@ static int show_all_names(sd_bus *bus) {
                 { "IconName",                    "s",  NULL,          offsetof(StatusInfo, icon_name)        },
                 { "Chassis",                     "s",  NULL,          offsetof(StatusInfo, chassis)          },
                 { "ChassisAssetTag",             "s",  NULL,          offsetof(StatusInfo, chassis_asset_tag)},
+                { "BoardAssetTag",               "s",  NULL,          offsetof(StatusInfo, board_asset_tag)  },
                 { "Deployment",                  "s",  NULL,          offsetof(StatusInfo, deployment)       },
                 { "Location",                    "s",  NULL,          offsetof(StatusInfo, location)         },
                 { "KernelName",                  "s",  NULL,          offsetof(StatusInfo, kernel_name)      },

src/hostname/hostnamed.c

@@ -386,6 +386,10 @@ static int get_chassis_asset_tag(Context *c, char **ret) {
         return get_dmi_property(c, "ID_CHASSIS_ASSET_TAG", ret);
 }
 
+static int get_board_asset_tag(Context *c, char **ret) {
+        return get_dmi_property(c, "ID_BOARD_ASSET_TAG", ret);
+}
+
 static int get_hardware_vendor(Context *c, char **ret) {
         return get_dmi_properties(c, STRV_MAKE_CONST("ID_VENDOR_FROM_DATABASE", "ID_VENDOR"), ret);
 }
@@ -1049,6 +1053,23 @@ static int property_get_chassis_asset_tag(
         return sd_bus_message_append(reply, "s", chassis_asset_tag);
 }
 
+static int property_get_board_asset_tag(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        _cleanup_free_ char *board_asset_tag = NULL;
+        Context *c = ASSERT_PTR(userdata);
+
+        (void) get_board_asset_tag(c, &board_asset_tag);
+
+        return sd_bus_message_append(reply, "s", board_asset_tag);
+}
+
 static int property_get_hostname(
                 sd_bus *bus,
                 const char *path,
@@ -1720,7 +1741,8 @@ static int method_get_machine_info(sd_bus_message *m, void *userdata, sd_bus_err
 static int build_describe_response(Context *c, bool privileged, sd_json_variant **ret) {
         _cleanup_free_ char *hn = NULL, *dhn = NULL, *in = NULL,
                 *chassis = NULL, *vendor = NULL, *model = NULL, *serial = NULL, *firmware_version = NULL,
-                *firmware_vendor = NULL, *chassis_asset_tag = NULL, *sku = NULL, *hardware_version = NULL;
+                *firmware_vendor = NULL, *chassis_asset_tag = NULL, *board_asset_tag = NULL,
+                *sku = NULL, *hardware_version = NULL;
         _cleanup_strv_free_ char **os_release_pairs = NULL, **machine_info_pairs = NULL;
         usec_t firmware_date = USEC_INFINITY, eol = USEC_INFINITY;
         _cleanup_(sd_json_variant_unrefp) sd_json_variant *v = NULL;
@@ -1770,6 +1792,7 @@ static int build_describe_response(Context *c, bool privileged, sd_json_variant
         (void) get_firmware_vendor(c, &firmware_vendor);
         (void) get_firmware_date(c, &firmware_date);
         (void) get_chassis_asset_tag(c, &chassis_asset_tag);
+        (void) get_board_asset_tag(c, &board_asset_tag);
 
         if (c->data[PROP_OS_SUPPORT_END])
                 (void) os_release_support_ended(c->data[PROP_OS_SUPPORT_END], /* quiet= */ false, &eol);
@@ -1797,6 +1820,7 @@ static int build_describe_response(Context *c, bool privileged, sd_json_variant
                         SD_JSON_BUILD_PAIR_STRING("IconName", in ?: c->data[PROP_ICON_NAME]),
                         SD_JSON_BUILD_PAIR_STRING("Chassis", chassis),
                         SD_JSON_BUILD_PAIR_STRING("ChassisAssetTag", chassis_asset_tag),
+                        SD_JSON_BUILD_PAIR_STRING("BoardAssetTag", board_asset_tag),
                         SD_JSON_BUILD_PAIR_STRING("Deployment", c->data[PROP_DEPLOYMENT]),
                         SD_JSON_BUILD_PAIR_STRING("Location", c->data[PROP_LOCATION]),
                         SD_JSON_BUILD_PAIR_STRING("KernelName", u.sysname),
@@ -1897,6 +1921,7 @@ static const sd_bus_vtable hostname_vtable[] = {
         SD_BUS_PROPERTY("BootID", "ay", property_get_boot_id, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("VSockCID", "u", property_get_vsock_cid, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("ChassisAssetTag", "s", property_get_chassis_asset_tag, 0, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("BoardAssetTag", "s", property_get_board_asset_tag, 0, SD_BUS_VTABLE_PROPERTY_CONST),
 
         SD_BUS_METHOD_WITH_ARGS("SetHostname",
                                 SD_BUS_ARGS("s", hostname, "b", interactive),

src/shared/varlink-io.systemd.Hostname.c

@@ -15,6 +15,8 @@ static SD_VARLINK_DEFINE_METHOD(
                 SD_VARLINK_DEFINE_OUTPUT(Chassis, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("An unique identifier of the system chassis."),
                 SD_VARLINK_DEFINE_OUTPUT(ChassisAssetTag, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_FIELD_COMMENT("An unique identifier of the system board."),
+                SD_VARLINK_DEFINE_OUTPUT(BoardAssetTag, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_DEFINE_OUTPUT(Deployment, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_DEFINE_OUTPUT(Location, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_DEFINE_OUTPUT(KernelName, SD_VARLINK_STRING, 0),