tools: add fdt_add_pubkey

Having to use the -K option to mkimage to populate U-Boot's .dtb with the
public key while signing the kernel FIT image is often a little
awkward. In particular, when using a meta-build system such as
bitbake/Yocto, having the tasks of the kernel and U-Boot recipes
intertwined, modifying deployed artifacts and rebuilding U-Boot with
an updated .dtb is quite cumbersome. Also, in some scenarios one may
wish to build U-Boot complete with the public key(s) embedded in the
.dtb without the corresponding private keys being present on the same
build host.

So this adds a simple tool that allows one to disentangle the kernel
and U-Boot builds, by simply copy-pasting just enough of the mkimage
code to allow one to add a public key to a .dtb. When using mkimage,
some of the information is taken from the .its used to build the
kernel (algorithm and key name), so that of course needs to be
supplied on the command line.

Signed-off-by: Roman Kopytin <Roman.Kopytin@kaspersky.com>
Signed-off-by: Ivan Mikhaylov <fr0st61te@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

3 files changed, 142 insertions, 0 deletions

diff --git a/tools/.gitignore b/tools/.gitignore
index 788ea260a0..cda3ea628c 100644
--- a/tools/.gitignore
+++ b/tools/.gitignore
@@ -6,6 +6,7 @@
 /dumpimage
 /easylogo/easylogo
 /envcrc
+/fdt_add_pubkey
 /fdtgrep
 /file2include
 /fit_check_sign
diff --git a/tools/Makefile b/tools/Makefile
index e13effbb66..38699b069d 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -65,6 +65,7 @@ mkenvimage-objs := mkenvimage.o os_support.o lib/crc32.o
 
 hostprogs-y += dumpimage mkimage
 hostprogs-$(CONFIG_TOOLS_LIBCRYPTO) += fit_info fit_check_sign
+hostprogs-$(CONFIG_TOOLS_LIBCRYPTO) += fdt_add_pubkey
 
 ifneq ($(CONFIG_CMD_BOOTEFI_SELFTEST)$(CONFIG_FWU_MDATA_GPT_BLK),)
 hostprogs-y += file2include
@@ -150,6 +151,7 @@ dumpimage-objs := $(dumpimage-mkimage-objs) dumpimage.o
 mkimage-objs   := $(dumpimage-mkimage-objs) mkimage.o
 fit_info-objs   := $(dumpimage-mkimage-objs) fit_info.o
 fit_check_sign-objs   := $(dumpimage-mkimage-objs) fit_check_sign.o
+fdt_add_pubkey-objs   := $(dumpimage-mkimage-objs) fdt_add_pubkey.o
 file2include-objs := file2include.o
 
 ifneq ($(CONFIG_MX23)$(CONFIG_MX28)$(CONFIG_TOOLS_LIBCRYPTO),)
@@ -187,6 +189,7 @@ HOSTCFLAGS_fit_image.o += -DMKIMAGE_DTC=\"$(CONFIG_MKIMAGE_DTC_PATH)\"
 HOSTLDLIBS_dumpimage := $(HOSTLDLIBS_mkimage)
 HOSTLDLIBS_fit_info := $(HOSTLDLIBS_mkimage)
 HOSTLDLIBS_fit_check_sign := $(HOSTLDLIBS_mkimage)
+HOSTLDLIBS_fdt_add_pubkey := $(HOSTLDLIBS_mkimage)
 
 hostprogs-$(CONFIG_EXYNOS5250) += mkexynosspl
 hostprogs-$(CONFIG_EXYNOS5420) += mkexynosspl
diff --git a/tools/fdt_add_pubkey.c b/tools/fdt_add_pubkey.c
new file mode 100644
index 0000000000..999f5a7e83
--- /dev/null
+++ b/tools/fdt_add_pubkey.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0+
+#include <image.h>
+#include "fit_common.h"
+
+static const char *cmdname;
+
+static const char *algo_name = "sha1,rsa2048"; /* -a <algo> */
+static const char *keydir = "."; /* -k <keydir> */
+static const char *keyname = "key"; /* -n <keyname> */
+static const char *require_keys; /* -r <conf|image> */
+static const char *keydest; /* argv[n] */
+
+static void print_usage(const char *msg)
+{
+	fprintf(stderr, "Error: %s\n", msg);
+	fprintf(stderr, "Usage: %s [-a <algo>] [-k <keydir>] [-n <keyname>] [-r <conf|image>]"
+			" <fdt blob>\n", cmdname);
+	fprintf(stderr, "Help information: %s [-h]\n", cmdname);
+	exit(EXIT_FAILURE);
+}
+
+static void print_help(void)
+{
+	fprintf(stderr, "Options:\n"
+		"\t-a <algo>       Cryptographic algorithm. Optional parameter, default value: sha1,rsa2048\n"
+		"\t-k <keydir>     Directory with public key. Optional parameter, default value: .\n"
+		"\t-n <keyname>    Public key name. Optional parameter, default value: key\n"
+		"\t-r <conf|image> Required: If present this indicates that the key must be verified for the image / configuration to be considered valid.\n"
+		"\t<fdt blob>      FDT blob file for adding of the public key. Required parameter.\n");
+	exit(EXIT_FAILURE);
+}
+
+static void process_args(int argc, char *argv[])
+{
+	int opt;
+
+	while ((opt = getopt(argc, argv, "a:k:n:r:h")) != -1) {
+		switch (opt) {
+		case 'k':
+			keydir = optarg;
+			break;
+		case 'a':
+			algo_name = optarg;
+			break;
+		case 'n':
+			keyname = optarg;
+			break;
+		case 'r':
+			require_keys = optarg;
+			break;
+		case 'h':
+			print_help();
+		default:
+			print_usage("Invalid option");
+		}
+	}
+	/* The last parameter is expected to be the .dtb to add the public key to */
+	if (optind < argc)
+		keydest = argv[optind];
+
+	if (!keydest)
+		print_usage("Missing dtb file to update");
+}
+
+static void reset_info(struct image_sign_info *info)
+{
+	if (!info)
+		fprintf(stderr, "Error: info is NULL in %s\n", __func__);
+
+	memset(info, 0, sizeof(struct image_sign_info));
+
+	info->keydir = keydir;
+	info->keyname = keyname;
+	info->name = algo_name;
+	info->require_keys = require_keys;
+	info->crypto = image_get_crypto_algo(algo_name);
+
+	if (!info->crypto) {
+		fprintf(stderr, "Unsupported signature algorithm '%s'\n",
+			algo_name);
+		exit(EXIT_FAILURE);
+	}
+}
+
+static int add_pubkey(struct image_sign_info *info)
+{
+	int destfd = -1, ret;
+	void *dest_blob = NULL;
+	struct stat dest_sbuf;
+	size_t size_inc = 0;
+
+	if (!info)
+		fprintf(stderr, "Error: info is NULL in %s\n", __func__);
+
+	do {
+		if (destfd >= 0) {
+			munmap(dest_blob, dest_sbuf.st_size);
+			close(destfd);
+
+			fprintf(stderr, ".dtb too small, increasing size by 1024 bytes\n");
+			size_inc = 1024;
+		}
+
+		destfd = mmap_fdt(cmdname, keydest, size_inc, &dest_blob,
+				  &dest_sbuf, false, false);
+		if (destfd < 0)
+			exit(EXIT_FAILURE);
+
+		ret = info->crypto->add_verify_data(info, dest_blob);
+		if (ret == -ENOSPC)
+			continue;
+		else if (ret < 0)
+			break;
+	} while (ret == -ENOSPC);
+
+	return ret;
+}
+
+int main(int argc, char *argv[])
+{
+	struct image_sign_info info;
+	int ret;
+
+	cmdname = argv[0];
+
+	process_args(argc, argv);
+	reset_info(&info);
+	ret = add_pubkey(&info);
+
+	if (ret < 0) {
+		fprintf(stderr, "%s: Cannot add public key to FIT blob: %s\n",
+			cmdname, strerror(ret));
+		exit(EXIT_FAILURE);
+	}
+
+	exit(EXIT_SUCCESS);
+}
+