[PXEXT] Add PXENV_FILE_EXEC call to PXE extensions API.

This allows pxelinux to execute arbitrary gPXE commands.  This is
remarkably unsafe (not least because some of the commands will assume
full ownership of memory and do nasty things like edit the e820 map
underneath the calling pxelinux), but it does allow access to the
"sanboot" command.

src/arch/i386/interface/pxe/pxe_call.c

 	PXENV_EXIT_t ( * file_select ) ( struct s_PXENV_FILE_SELECT * );
 	PXENV_EXIT_t ( * file_read ) ( struct s_PXENV_FILE_READ * );
 	PXENV_EXIT_t ( * get_file_size ) ( struct s_PXENV_GET_FILE_SIZE * );
+	PXENV_EXIT_t ( * file_exec ) ( struct s_PXENV_FILE_EXEC * );
 };
 
 /**
 		pxenv_call.get_file_size = pxenv_get_file_size;
 		param_len = sizeof ( pxenv_any.get_file_size );
 		break;
+	case PXENV_FILE_EXEC:
+		pxenv_call.file_exec = pxenv_file_exec;
+		param_len = sizeof ( pxenv_any.file_exec );
+		break;
 	default:
 		DBG ( "PXENV_UNKNOWN_%hx", opcode );
 		pxenv_call.unknown = pxenv_unknown;

src/include/pxe.h

 	struct s_PXENV_FILE_SELECT		file_select;
 	struct s_PXENV_FILE_READ		file_read;
 	struct s_PXENV_GET_FILE_SIZE		get_file_size;
+	struct s_PXENV_FILE_EXEC		file_exec;
 };
 
 typedef union u_PXENV_ANY PXENV_ANY_t;

src/include/pxe_api.h

 
 /** @} */ /* pxenv_get_file_size */
 
+/** @defgroup pxenv_file_exec PXENV_FILE_EXEC
+ *
+ * FILE EXEC
+ *
+ * @{
+ */
+
+/** PXE API function code for pxenv_file_exec() */
+#define PXENV_FILE_EXEC			0x00e5
+
+/** Parameter block for pxenv_file_exec() */
+struct s_PXENV_FILE_EXEC {
+	PXENV_STATUS_t Status;		/**< PXE status code */
+	SEGOFF16_t Command;		/**< Command to execute */
+} PACKED;
+
+typedef struct s_PXENV_FILE_EXEC PXENV_FILE_EXEC_t;
+
+extern PXENV_EXIT_t pxenv_file_exec ( struct s_PXENV_FILE_EXEC *file_exec );
+
+/** @} */ /* pxenv_file_exec */
+
 /** @} */ /* pxe_file_api */
 
 /** @defgroup pxe_loader_api PXE Loader API

src/interface/pxe/pxe_file.c

  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
-FEATURE ( FEATURE_MISC, "PXEXT", DHCP_EB_FEATURE_PXE_EXT, 1 );
+FEATURE ( FEATURE_MISC, "PXEXT", DHCP_EB_FEATURE_PXE_EXT, 2 );
 
 /**
  * FILE OPEN
 	get_file_size->Status = PXENV_STATUS_SUCCESS;
 	return PXENV_EXIT_SUCCESS;
 }
+
+/**
+ * FILE EXEC
+ *
+ * @v file_exec				Pointer to a struct s_PXENV_FILE_EXEC
+ * @v s_PXENV_FILE_EXEC::Command	Command to execute
+ * @ret #PXENV_EXIT_SUCCESS		Command was executed successfully
+ * @ret #PXENV_EXIT_FAILURE		Command was not executed successfully
+ * @ret s_PXENV_FILE_EXEC::Status	PXE status code
+ *
+ */
+PXENV_EXIT_t pxenv_file_exec ( struct s_PXENV_FILE_EXEC *file_exec ) {
+	userptr_t command;
+	size_t command_len;
+	int rc;
+
+	DBG ( "PXENV_FILE_EXEC" );
+
+	/* Copy name from external program, and exec it */
+	command = real_to_user ( file_exec->Command.segment,
+				 file_exec->Command.offset );
+	command_len = strlen_user ( command, 0 );
+	{
+		char command_string[ command_len + 1 ];
+
+		copy_from_user ( command_string, command, 0,
+				 sizeof ( command_string ) );
+		DBG ( " %s", command_string );
+
+		if ( ( rc = system ( command_string ) ) != 0 ) {
+			file_exec->Status = PXENV_STATUS ( rc );
+			return PXENV_EXIT_FAILURE;
+		}
+	}
+
+	file_exec->Status = PXENV_STATUS_SUCCESS;
+	return PXENV_EXIT_SUCCESS;
+}