[PATCH] tools: add fdt_add_pubkey

[Roman Kopytin <Roman.Kopytin@kaspersky.com>]

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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>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

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From f4dd0edaec5fdac5d355eb5bef3f917b35d6c091 Mon Sep 17 00:00:00 2001
From: Roman Kopytin <Roman.Kopytin@kaspersky.com>
Date: Tue, 3 Aug 2021 12:48:15 +0300
Subject: [PATCH] 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>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
---
 tools/.gitignore       |  1 +
 tools/Makefile         |  3 ++
 tools/fdt_add_pubkey.c | 97 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 101 insertions(+)
 create mode 100755 tools/fdt_add_pubkey.c

diff --git a/tools/.gitignore b/tools/.gitignore
index a88453f64d..f312b760e4 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 4a86321f64..44f25dda18 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -73,6 +73,7 @@ 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
 
 hostprogs-$(CONFIG_CMD_BOOTEFI_SELFTEST) += file2include
 
@@ -153,6 +154,7 @@ 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)$(CONFIG_TOOLS_LIBCRYPTO),)
@@ -190,6 +192,7 @@ HOSTCFLAGS_fit_image.o += -DMKIMAGE_DTC=\"$(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 100755
index 0000000000..9306ecedd1
--- /dev/null
+++ b/tools/fdt_add_pubkey.c
@@ -0,0 +1,97 @@
+#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 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);
+	exit(EXIT_FAILURE);
+}
+
+static void process_args(int argc, char *argv[])
+{
+	int opt;
+
+	while((opt = getopt(argc, argv, "a:k:n:r:")) != -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;
+		default:
+			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)
+		usage("Missing dtb file to update");
+}
+
+int main(int argc, char *argv[])
+{
+	struct image_sign_info info;
+	int destfd, ret;
+	void *dest_blob = NULL;
+	struct stat dest_sbuf;
+	size_t size_inc = 0;
+
+	cmdname = argv[0];
+
+	process_args(argc, argv);
+
+	memset(&info, 0, sizeof(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);
+	}
+
+	while (1) {
+		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);
+
+		munmap(dest_blob, dest_sbuf.st_size);
+		close(destfd);
+		if (!ret || ret != -ENOSPC)
+			break;
+		fprintf(stderr, ".dtb too small, increasing size by 1024 bytes\n");
+		size_inc = 1024;
+	}
+
+	if (ret) {
+		fprintf(stderr, "%s: Cannot add public key to FIT blob: %s\n",
+			cmdname, strerror(-ret));
+		exit(EXIT_FAILURE);
+	}
+
+	exit(EXIT_SUCCESS);
+}
+
-- 
2.25.1