firmware-utils: zytrx: Add util for ZyXEL specific header

The ZyXEL NR7101 prepend an additional header to U-Boot images. This
header use the TRX magic 0x30524448 (HDR0), but is incompatible with
TRX images.

This code is reverse-engineered based on matching 32 bit numbers
found in the header with lengths and different checksum
calculations of the vendor images found on the device.  The result
was matched against the validation output produced by the
bootloader to name the associated header fields.

Example bootloader validation output:

 Zyxel TRX Image 1 --> Found!  Header Checksum OK
 ============ZyXEL header information==================
         chipId             : MT7621A
         boardId            : NR7101
         modelId            : 07 01 00 01
         kernel_len         : (14177560)
         kernelChksum       : (0x8DD31F69)
         swVersionInt       : 1.00(ABUV.0)D1
         swVersionExt       : 1.00(ABUV.0)D1

 Zyxel TRX Image 2 --> Found!  Header Checksum OK
 ============ZyXEL header information==================
         chipId             : MT7621A
         boardId            : NR7101
         modelId            : 07 01 00 01
         kernel_len         : (14176660)
         kernelChksum       : (0x951A7637)
         swVersionInt       : 1.00(ABUV.0)D0
         swVersionExt       : 1.00(ABUV.0)D0

 =================================================
 Check image validation:
 Image1 Header Magic Number --> OK
 Image2 Header Magic Number --> OK
 Image1 Header Checksum --> OK
 Image2 Header Checksum --> OK
 Image1 Data Checksum --> OK
 Image2 Data Checksum --> OK
 Image1 Stable Flag --> Stable
 Image1 Try Counter --> 0
 Image1: OK
 Image2: OK

The coverage and algorithm for the kernelChksum field is unknown.
This field is not validated by the bootloader or the OEM firmware
upgrade tool. It is therefore set to a static value for now.

The swVersion fields contain free form string values.  The OEM firmware
use ZyXEL structured version numbers as shown above.  The strings are
not interpreted or validated on boot, so they can be repurposed for
anything we want the bootloader to display to the user.  But the OEM
web GUI fails to flash images with freeform strings.

The purpose of the other strings in the header is not known.  The
values appear to be static.  We assume they are fixed for now, until
we have other examples.  One of these strings is the platform name,
which is taken as an input parameter for support other members of
the device family.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Tested-by: Bjørn Mork <bjorn@mork.no>
(cherry picked from commit 48cad07a55246317d66fee4ced25cb62a2bae3d3)

2 files changed, 227 insertions, 0 deletions

diff --git a/tools/firmware-utils/Makefile b/tools/firmware-utils/Makefile
index 28f8f0555a..cec8398a27 100644
--- a/tools/firmware-utils/Makefile
+++ b/tools/firmware-utils/Makefile
@@ -97,6 +97,7 @@ define Host/Compile
 	$(call cc,wrt400n cyg_crc32)
 	$(call cc,xorimage)
 	$(call cc,zyimage,-Wall)
+	$(call cc,zytrx,-Wall)
 	$(call cc,zyxbcm)
 endef
 
diff --git a/tools/firmware-utils/src/zytrx.c b/tools/firmware-utils/src/zytrx.c
new file mode 100644
index 0000000000..302efc6010
--- /dev/null
+++ b/tools/firmware-utils/src/zytrx.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * zytrx - add header to images for ZyXEL NR7101
+ *
+ * Based on add_header.c - partially based on OpenWrt's
+ * motorola-bin.c
+ *
+ * Copyright (C) 2008 Imre Kaloz  <kaloz@openwrt.org>
+ *                    Gabor Juhos <juhosg@openwrt.org>
+ * Copyright (C) 2021 Bjørn Mork <bjorn@mork.no>
+
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License,
+ * version 2 as published by the Free Software Foundation.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <string.h>
+#include <netinet/in.h>
+#include <inttypes.h>
+
+#define BPB 8 /* bits/byte */
+
+static uint32_t crc32[1<<BPB];
+
+static void init_crc32(void)
+{
+	const uint32_t poly = ntohl(0x2083b8ed);
+	int n;
+
+	for (n = 0; n < 1<<BPB; n++) {
+		uint32_t crc = n;
+		int bit;
+
+		for (bit = 0; bit < BPB; bit++)
+			crc = (crc & 1) ? (poly ^ (crc >> 1)) : (crc >> 1);
+		crc32[n] = crc;
+	}
+}
+
+static uint32_t crc32buf(const unsigned char *buf, size_t len)
+{
+	uint32_t crc = 0xFFFFFFFF;
+
+	for (; len; len--, buf++)
+		crc = crc32[(uint8_t)crc ^ *buf] ^ (crc >> BPB);
+	return ~crc;
+}
+
+/* HDR0 reversed, to be stored as BE */
+#define MAGIC		0x30524448  /* HDR0 reversed, to be stored as BE */
+
+/* All numbers are stored as BE */
+struct zytrx_t {
+	uint32_t magic;
+	uint32_t len_h;		/* Length of this header */
+	uint32_t len_t;		/* Total length of file  */
+	uint32_t crc32_p;	/* Bit inverted 32-bit CRC of image payload */
+	uint8_t  verInt[32];	/* String "5.0.0.0\n" zero padded */
+	uint8_t  verExt[32];	/* String "\n" zero padded */
+	uint32_t len_p;		/* Length of image payload */
+	uint8_t  pad1[12];	/* zero padding(?) */
+	uint8_t  code[164];	/* string "3 6035 122 0\n" zero padded */
+	uint8_t  chipid[8];	/* string "MT7621A" zero padded */
+	uint8_t  boardid[16];	/* string "NR7101" zero padded */
+	uint32_t modelid;	/* modelid as 4 BCD digits: 0x07010001 */
+	uint8_t  pad2[8];	/* zero padding(?) */
+	uint8_t  swVersionInt[32];	/* ZyXEL version string: "1.00(ABUV.0)D0" zero padded */
+	uint8_t  swVersionExt[32];	/* identical to swVersionInt  */
+	uint8_t  pad4[4];	/* zero padding(?) */
+	uint32_t kernelChksum;	/* no idea how this is computed - reported but not validated */
+	uint8_t  pad5[4];	/* zero padding(?) */
+	uint32_t crc32_h;	/* Bit inverted 32-bit CRC of this header payload */
+	uint8_t  pad6[4];	/* zero padding(?) */
+};
+
+/* static?() field values of unknown meaning - maybe ove to board
+ * table when we know the significance
+ */
+#define VER_INT		"5.0.0.0\n"
+#define VER_EXT		"\n"
+#define CODE		"3 6035 122 0\n"
+#define KERNELCHKSUM	0x12345678
+
+/* table of supported devices using this header format */
+static struct board_t {
+	uint8_t  chipid[8];
+	uint8_t  boardid[16];
+	uint32_t modelid;
+} boards[] = {
+	{ "MT7621A", "NR7101", 0x07010001 },
+	{}
+};
+
+static int find_board(struct zytrx_t *h, char *board)
+{
+	struct board_t *p;
+
+	for (p = boards; p->modelid; p++) {
+		if (strncmp((const char *)p->boardid, board, sizeof(p->boardid)))
+			continue;
+		memcpy(h->chipid, p->chipid, sizeof(h->chipid));
+		memcpy(h->boardid, p->boardid, sizeof(h->boardid));
+		h->modelid = htonl(p->modelid);
+		return 0;
+	}
+	return -1;
+}
+
+static void usage(const char *name)
+{
+	struct board_t *p;
+
+	fprintf(stderr, "Usage:\n");
+	fprintf(stderr, " %s -B <board> -v <versionstr> -i <file> [-o <outputfile>]\n\n", name);
+	fprintf(stderr, "Supported <board> values:\n");
+	for (p = boards; p->modelid; p++)
+		fprintf(stderr, "\t%-12s\n", p->boardid);
+	fprintf(stderr, "\nExample:\n");
+	fprintf(stderr, " %s -B %s -v foobar-1.0 -i my.img -o out.img\n\n", name,
+		boards[0].boardid);
+	exit(EXIT_FAILURE);
+}
+
+static void errexit(const char *msg)
+{
+	fprintf(stderr, "ERR: %s: %s\n", msg, errno ? strerror(errno) : "unknown");
+	exit(EXIT_FAILURE);
+}
+
+static void *map_input(const char *name, size_t *len)
+{
+	struct stat stat;
+	void *mapped;
+	int fd;
+
+	fd = open(name, O_RDONLY);
+	if (fd < 0)
+		return NULL;
+	if (fstat(fd, &stat) < 0) {
+		close(fd);
+		return NULL;
+	}
+	*len = stat.st_size;
+	mapped = mmap(NULL, stat.st_size, PROT_READ, MAP_SHARED, fd, 0);
+	if (close(fd) < 0)
+		return NULL;
+	return mapped;
+}
+
+int main(int argc, char **argv)
+{
+	int c, fdout = STDOUT_FILENO;
+	void *input_file = NULL;
+	size_t file_len, len;
+	uint32_t crc;
+	struct zytrx_t h = {
+		.magic		= htonl(MAGIC),
+		.len_h		= htonl(sizeof(h)),
+		.verInt		= VER_INT,
+		.verExt		= VER_EXT,
+		.code		= CODE,
+		.kernelChksum	= htonl(KERNELCHKSUM),
+	};
+
+	while ((c = getopt(argc, argv, "B:v:i:o:")) != -1) {
+		switch (c) {
+		case 'B':
+			if (find_board(&h, optarg) < 0)
+				errexit("unsupported board");
+			break;
+		case 'v':
+			len = strlen(optarg);
+			if (len > sizeof(h.swVersionInt))
+				errexit("version string too long");
+			memcpy(h.swVersionInt, optarg, len);
+			memcpy(h.swVersionExt, optarg, len);
+			break;
+		case 'i':
+			input_file = map_input(optarg, &file_len);
+			if (!input_file)
+				errexit(optarg);
+			break;
+		case 'o':
+			fdout = open(optarg, O_WRONLY | O_CREAT, 0644);
+			if (fdout < 0)
+				errexit(optarg);
+			break;
+		default:
+			usage(argv[0]);
+		}
+	}
+
+	/* required paremeters */
+	if (!input_file || !h.modelid || !h.swVersionInt[0])
+		usage(argv[0]);
+
+	/* length fields */
+	h.len_t = htonl(sizeof(h) + file_len);
+	h.len_p = htonl(file_len);
+
+	/* crc fields */
+	init_crc32();
+	crc = crc32buf(input_file, file_len);
+	h.crc32_p = htonl(~crc);
+	crc = crc32buf((unsigned char *)&h, sizeof(h));
+	h.crc32_h = htonl(~crc);
+
+	/* dump new image */
+	write(fdout, &h, sizeof(h));
+	write(fdout, input_file, file_len);
+
+	/* close files */
+	munmap(input_file, file_len);
+	if (fdout != STDOUT_FILENO)
+		close(fdout);
+
+	return EXIT_SUCCESS;
+}