[efi] Add "shim" command

Allow a shim to be used to facilitate booting a kernel using a script
such as:

    kernel /images/vmlinuz console=ttyS0,115200n8
    initrd /images/initrd.img
    shim /images/shimx64.efi
    boot

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/config.c

@@ -290,6 +290,9 @@ REQUIRE_OBJECT ( cert_cmd );
 #ifdef IMAGE_MEM_CMD
 REQUIRE_OBJECT ( image_mem_cmd );
 #endif
+#ifdef SHIM_CMD
+REQUIRE_OBJECT ( shim_cmd );
+#endif
 
 /*
  * Drag in miscellaneous objects

src/config/defaults/efi.h

@@ -47,6 +47,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define USB_BLOCK		/* USB block devices */
 
 #define	REBOOT_CMD		/* Reboot command */
+#define SHIM_CMD		/* EFI shim command */
 
 #if defined ( __i386__ ) || defined ( __x86_64__ )
 #define IOAPI_X86

src/config/general.h

@@ -160,6 +160,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 //#define CERT_CMD		/* Certificate management commands */
 //#define IMAGE_MEM_CMD		/* Read memory command */
 #define IMAGE_ARCHIVE_CMD	/* Archive image management commands */
+//#define SHIM_CMD		/* EFI shim command */
 
 /*
  * ROM-specific options

src/hci/commands/shim_cmd.c

@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2023 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <getopt.h>
+#include <ipxe/command.h>
+#include <ipxe/parseopt.h>
+#include <ipxe/efi/efi_image.h>
+#include <usr/imgmgmt.h>
+#include <usr/shimmgmt.h>
+
+/** @file
+ *
+ * EFI shim command
+ *
+ */
+
+/** "shim" options */
+struct shim_options {
+	/** Download timeout */
+	unsigned long timeout;
+	/** Require third party loader */
+	int require_loader;
+	/** Allow PXE base code protocol */
+	int allow_pxe;
+};
+
+/** "shim" option list */
+static struct option_descriptor shim_opts[] = {
+	OPTION_DESC ( "timeout", 't', required_argument,
+		      struct shim_options, timeout, parse_timeout ),
+	OPTION_DESC ( "require-loader", 'l', no_argument,
+		      struct shim_options, require_loader, parse_flag ),
+	OPTION_DESC ( "allow-pxe", 'p', no_argument,
+		      struct shim_options, allow_pxe, parse_flag ),
+};
+
+/** "shim" command descriptor */
+static struct command_descriptor shim_cmd =
+	COMMAND_DESC ( struct shim_options, shim_opts, 0, 1, NULL );
+
+/**
+ * The "shim" command
+ *
+ * @v argc		Argument count
+ * @v argv		Argument list
+ * @ret rc		Return status code
+ */
+static int shim_exec ( int argc, char **argv ) {
+	struct shim_options opts;
+	struct image *image = NULL;
+	struct image *kernel;
+	char *name_uri;
+	int download;
+	int rc;
+
+	/* Parse options */
+	if ( ( rc = parse_options ( argc, argv, &shim_cmd, &opts ) ) != 0 )
+		goto err_parse;
+
+	/* Decide whether or not to download images */
+	kernel = find_image_tag ( &selected_image );
+	download = ( ! ( kernel && efi_can_load ( kernel ) ) );
+
+	/* Parse name/URI string */
+	name_uri = argv[optind];
+
+	/* Acquire image, if applicable */
+	if ( download && name_uri &&
+	     ( ( rc = imgacquire ( name_uri, opts.timeout,
+				   &image ) ) != 0 ) ) {
+		goto err_image;
+	}
+
+	/* (Un)register as shim */
+	if ( ( rc = shim ( image, opts.require_loader, opts.allow_pxe ) ) != 0 )
+		goto err_shim;
+
+ err_shim:
+ err_image:
+ err_parse:
+	return rc;
+}
+
+/** Shim commands */
+struct command shim_commands[] __command = {
+	{
+		.name = "shim",
+		.exec = shim_exec,
+	},
+};