igvm: add command line parameter support

Add a "cmdline" property to the igvm-cfg object and a handler for the
IGVM_VHT_COMMAND_LINE directive, which copies the string into the
parameter area the directive points at.

The command line is passed to whatever software the IGVM file loads,
such as an SVSM. For example, SVSM can use it to select the serial port
it logs to.

Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-ID: <20261019-igvm_command_line-v3-1-29aeacbd6cd7@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

backends/igvm-cfg.c

@@ -34,6 +34,19 @@ static void set_igvm(Object *obj, const char *value, Error **errp)
     igvm->filename = g_strdup(value);
 }
 
+static char *get_cmdline(Object *obj, Error **errp)
+{
+    IgvmCfg *igvm = IGVM_CFG(obj);
+    return g_strdup(igvm->cmdline);
+}
+
+static void set_cmdline(Object *obj, const char *value, Error **errp)
+{
+    IgvmCfg *igvm = IGVM_CFG(obj);
+    g_free(igvm->cmdline);
+    igvm->cmdline = g_strdup(value);
+}
+
 static ResettableState *igvm_reset_state(Object *obj)
 {
     IgvmCfg *igvm = IGVM_CFG(obj);
@@ -85,6 +98,13 @@ static void igvm_cfg_class_init(ObjectClass *oc, const void *data)
     object_class_property_set_description(oc, "file",
                                           "Set the IGVM filename to use");
 
+    object_class_property_add_str(oc, "cmdline", get_cmdline, set_cmdline);
+    object_class_property_set_description(oc, "cmdline",
+                                          "Set the command line for the "
+                                          "software loaded from the IGVM "
+                                          "file (copied verbatim, not "
+                                          "parsed by QEMU)");
+
     igvmc->process = qigvm_process_file;
 
     rc->get_state = igvm_reset_state;
@@ -112,4 +132,5 @@ static void igvm_cfg_finalize(Object *obj)
         igvm_free(igvm->file);
     }
     g_free(igvm->filename);
+    g_free(igvm->cmdline);
 }

backends/igvm.c

@@ -161,6 +161,8 @@ static int qigvm_directive_snp_id_block(QIgvm *ctx, const uint8_t *header_data,
 static int qigvm_initialization_guest_policy(QIgvm *ctx,
                                        const uint8_t *header_data,
                                        Error **errp);
+static int qigvm_directive_command_line(QIgvm *ctx, const uint8_t *header_data,
+                                        Error **errp);
 #ifdef CONFIG_FDT
 static int qigvm_directive_device_tree(QIgvm *ctx, const uint8_t *header_data,
                                        Error **errp);
@@ -195,6 +197,8 @@ static struct QIGVMHandler handlers[] = {
       qigvm_initialization_guest_policy },
     { IGVM_VHT_MADT, IGVM_HEADER_SECTION_DIRECTIVE,
       qigvm_directive_madt },
+    { IGVM_VHT_COMMAND_LINE, IGVM_HEADER_SECTION_DIRECTIVE,
+      qigvm_directive_command_line },
 #ifdef CONFIG_FDT
     { IGVM_VHT_DEVICE_TREE, IGVM_HEADER_SECTION_DIRECTIVE,
       qigvm_directive_device_tree },
@@ -869,6 +873,33 @@ static int qigvm_directive_snp_id_block(QIgvm *ctx, const uint8_t *header_data,
     return 0;
 }
 
+static int qigvm_directive_command_line(QIgvm *ctx, const uint8_t *header_data,
+                                        Error **errp)
+{
+    const IGVM_VHS_PARAMETER *param = (const IGVM_VHS_PARAMETER *)header_data;
+    const char *cmdline = ctx->cfg->cmdline ? ctx->cfg->cmdline : "";
+    uint8_t *param_data;
+    uint32_t param_size;
+    size_t cmdline_size = strlen(cmdline) + 1;
+
+    param_data = qigvm_get_param_data(ctx, param, &param_size, errp);
+    if (!param_data) {
+        return -1;
+    }
+
+    if (cmdline_size > param_size) {
+        error_setg(errp,
+                   "IGVM: command line size %zu exceeds the %u byte "
+                   "parameter area defined in IGVM file",
+                   cmdline_size, param_size);
+        return -1;
+    }
+
+    memcpy(param_data, cmdline, cmdline_size);
+
+    return 0;
+}
+
 #ifdef CONFIG_FDT
 static int qigvm_directive_device_tree(QIgvm *ctx, const uint8_t *header_data,
                                        Error **errp)

include/system/igvm-internal.h

@@ -32,6 +32,11 @@ struct IgvmCfg {
      *           format.
      */
     char *filename;
+    /*
+     * cmdline: Command line for the software loaded from the IGVM file,
+     *          if it asks for one.
+     */
+    char *cmdline;
     IgvmHandle file;
     ResettableState reset_state;
     QTAILQ_HEAD(, IgvmMemoryRegion) memory_regions;

qapi/qom.json

@@ -977,11 +977,16 @@
 #
 # @file: IGVM file to use to configure guest
 #
+# @cmdline: command line for the software loaded from the IGVM file.
+#     Its format is specific to that software.  Passed verbatim: QEMU
+#     does not parse it.
+#     Ignored if the IGVM file does not ask for one.  (since 11.2)
+#
 # Since: 10.1
 ##
 { 'struct': 'IgvmCfgProperties',
   'if': 'CONFIG_IGVM',
-  'data': { 'file': 'str' } }
+  'data': { 'file': 'str', '*cmdline': 'str' } }
 
 ##
 # @SevCommonProperties:

qemu-options.hx

@@ -6496,7 +6496,7 @@ SRST
                  -machine ...,confidential-guest-support=tdx \\
                  ......
 
-    ``-object igvm-cfg,file=file``
+    ``-object igvm-cfg,file=file[,cmdline=string]``
         Create an IGVM configuration object that defines the initial state
         of the guest using a file in that conforms to the Independent Guest
         Virtual Machine (IGVM) file format.
@@ -6509,6 +6509,10 @@ SRST
         memory of the virtual machine and, depending on the platform, can
         define the initial processor state, memory map and parameters.
 
+        The optional ``cmdline`` parameter is a command line passed
+        verbatim to the software loaded from the IGVM file, if the file
+        requests one. Its format is specific to that software.
+
         The IGVM file is expected to contain the firmware for the virtual
         machine, therefore an ``igvm-cfg`` object cannot be provided along
         with other ways of specifying firmware, such as the ``-bios``