--- /dev/null
+/*
+ * jcgimage - Create a JCG firmware image
+ *
+ * Copyright (C) 2015 Reinhard Max <reinhard@m4x.de>
+ *
+ * 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 (at your option) 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ */
+
+/*
+ * JCG firmware update images consist of a 512 byte header and a
+ * modified uImage (details below) as the payload.
+ *
+ * The payload is obfuscated by XORing it with a key that is generated
+ * from parts of the header. Fortunately only non-essential parts of
+ * the header are used for this and zeroing them results in a zero
+ * key, effectively disabling the obfuscation and allowing us to use
+ * clear text payloads.
+ *
+ * The mandatory parts of the header are:
+ *
+ * - A magic string of "YSZJ" at offset 0.
+ * - A value of 1 at offset 39 (header format version?)
+ * - A CRC32 checksum of the payload at offset 504.
+ * - A CRC32 checksum of the header at offset 508.
+ *
+ * An image constructed by these rules will be accepted by JCG's
+ * U-Boot in resuce mode via TFTP and the payload will be written to
+ * the flash starting at offset 0x00050000.
+ *
+ * JCG's U-Boot does check the content or size of the payload
+ * image. If it is too large, it wraps around and overwrites U-Boot,
+ * requiring JTAG to revive the board. To prevent such bricking from
+ * happening, this tool refuses to build such overlong images.
+ *
+ * Two more conditions have to be met for a JCG image to be accepted
+ * as a valid update by the web interface of the stock firware:
+ *
+ * - The bytes at offsets 109 and 111 in the header must be a binary
+ * representation of the first two components of the firmware
+ * version as displayed in the update web form, or it will be
+ * rejected as "incorrect product".
+ *
+ * - The payload must start with a valid uImage header whose data
+ * CRC checksum matches the whole rest of the update file rather
+ * than just the number of bytes specified in the size field of the
+ * header.
+ *
+ * This last condition is met by JCG's original firmware images,
+ * because they have both, kernel and rootfs inside the uImage and
+ * abuse the last four bytes of the name field to record the offset of
+ * the file system from the start of the uImage header. This tool
+ * produces such images when called with -k and -r, which are meant to
+ * repack the original firmware after modifying the file systen,
+ * e.g. to add debugging tools and enable shell access.
+ *
+ * In contrast, OpenWrt sysupgrade images consist of a uImage that
+ * only contains the kernel and has the rootfs appended to it. Hence,
+ * the CRC over kernel and file system does not match the one in the
+ * uImage header. Fixing this by adjusting the uImage header is not
+ * possible, because it makes the uImage unusable for booting. Instead
+ * we append four "patch" bytes to the end of the file system, that
+ * are calculated to force the checksum of kernel+fs to be the same as
+ * for the kernel alone.
+ *
+ */
+
+#include <zlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <libgen.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <err.h>
+#include <time.h>
+#include <sys/mman.h>
+#include <arpa/inet.h>
+#include <assert.h>
+
+/*
+ * JCG Firmware image header
+ */
+#define JH_MAGIC 0x59535a4a /* "YSZJ" */
+struct jcg_header {
+ uint32_t jh_magic;
+ uint8_t jh_version[32]; /* Firmware version string. Fill with
+ zeros to avoid encryption */
+ uint32_t jh_type; /* must be 1 */
+ uint8_t jh_info[64]; /* Firmware info string. Fill with
+ zeros to avoid encryption */
+ uint32_t jh_time; /* Image creation time in seconds since
+ * the Epoch. Does not seem to be used
+ * by the stock firmware. */
+ uint16_t jh_major; /* Major fimware version */
+ uint16_t jh_minor; /* Minor fimrmware version */
+ uint8_t jh_unknown[392]; /* Apparently unused and all zeros */
+ uint32_t jh_dcrc; /* CRC checksum of the payload */
+ uint32_t jh_hcrc; /* CRC checksum of the header */
+};
+
+/*
+ * JCG uses a modified uImage header that replaces the last four bytes
+ * of the image name with the length of the kernel in the image.
+ */
+#define IH_MAGIC 0x27051956 /* Image Magic Number */
+#define IH_NMLEN 28 /* Image Name Length */
+
+struct uimage_header {
+ uint32_t ih_magic; /* Image Header Magic Number */
+ uint32_t ih_hcrc; /* Image Header CRC Checksum */
+ uint32_t ih_time; /* Image Creation Timestamp */
+ uint32_t ih_size; /* Image Data Size */
+ uint32_t ih_load; /* Data Load Address */
+ uint32_t ih_ep; /* Entry Point Address */
+ uint32_t ih_dcrc; /* Image Data CRC Checksum */
+ uint8_t ih_os; /* Operating System */
+ uint8_t ih_arch; /* CPU architecture */
+ uint8_t ih_type; /* Image Type */
+ uint8_t ih_comp; /* Compression Type */
+ uint8_t ih_name[IH_NMLEN];/* Image Name */
+ uint32_t ih_fsoff; /* Offset of the file system partition */
+};
+
+/*
+ * Open the named file and return its size and file descriptor.
+ * Exit in case of errors.
+ */
+int
+opensize(char *name, size_t *size)
+{
+ struct stat s;
+ int fd = open(name, O_RDONLY);
+ if (fd < 0) {
+ err(1, "cannot open \"%s\"", name);
+ }
+ if (fstat(fd, &s) == -1) {
+ err(1, "cannot stat \"%s\"", name);
+ }
+ *size = s.st_size;
+ return fd;
+}
+
+/*
+ * Write the JCG header
+ */
+void
+mkjcgheader(struct jcg_header *h, size_t psize, char *version)
+{
+ uLong crc;
+ uint16_t major = 0, minor = 0;
+ void *payload = (void *)h + sizeof(*h);
+
+ if (version != NULL) {
+ if (sscanf(version, "%hu.%hu", &major, &minor) != 2) {
+ err(1, "cannot parse version \"%s\"", version);
+ }
+ }
+
+ memset(h, 0, sizeof(*h));
+ h->jh_magic = htonl(JH_MAGIC);
+ h->jh_type = htonl(1);
+ h->jh_time = htonl(time(NULL));
+ h->jh_major = htons(major);
+ h->jh_minor = htons(minor);
+
+ /* CRC over JCG payload (uImage) */
+ crc = crc32(0L, Z_NULL, 0);
+ crc = crc32(crc, payload, psize);
+ h->jh_dcrc = htonl(crc);
+
+ /* CRC over JCG header */
+ crc = crc32(0L, Z_NULL, 0);
+ crc = crc32(crc, (void *)h, sizeof(*h));
+ h->jh_hcrc = htonl(crc);
+}
+
+/*
+ * Write the uImage header
+ */
+void
+mkuheader(struct uimage_header *h, size_t ksize, size_t fsize)
+{
+ uLong crc;
+ void *payload = (void *)h + sizeof(*h);
+
+ // printf("mkuheader: %p, %zd, %zd\n", h, ksize, fsize);
+ memset(h, 0, sizeof(*h));
+ h->ih_magic = htonl(IH_MAGIC);
+ h->ih_time = htonl(time(NULL));
+ h->ih_size = htonl(ksize + fsize);
+ h->ih_load = htonl(0x80000000);
+ h->ih_ep = htonl(0x80292000);
+ h->ih_os = 0x05;
+ h->ih_arch = 0x05;
+ h->ih_type = 0x02;
+ h->ih_comp = 0x03;
+ h->ih_fsoff = htonl(sizeof(*h) + ksize);
+ strcpy((char *)h->ih_name, "Linux Kernel Image");
+
+ /* CRC over uImage payload (kernel and file system) */
+ crc = crc32(0L, Z_NULL, 0);
+ crc = crc32(crc, payload, ntohl(h->ih_size));
+ h->ih_dcrc = htonl(crc);
+ printf("CRC1: %08lx\n", crc);
+
+ /* CRC over uImage header */
+ crc = crc32(0L, Z_NULL, 0);
+ crc = crc32(crc, (void *)h, sizeof(*h));
+ h->ih_hcrc = htonl(crc);
+ printf("CRC2: %08lx\n", crc);
+}
+
+/*
+ * Calculate a "patch" value and write it into the last four bytes of
+ * buf, so that the CRC32 checksum of the whole buffer is dcrc.
+ *
+ * Based on: SAR-PR-2006-05: Reversing CRC – Theory and Practice.
+ * Martin Stigge, Henryk Plötz, Wolf Müller, Jens-Peter Redlich.
+ * http://sar.informatik.hu-berlin.de/research/publications/#SAR-PR-2006-05
+ */
+void
+craftcrc(uint32_t dcrc, uint8_t *buf, size_t len)
+{
+ int i;
+ uint32_t a;
+ uint32_t patch = 0;
+ uint32_t crc = crc32(0L, Z_NULL, 0);
+
+ a = ~dcrc;
+ for (i = 0; i < 32; i++) {
+ if (patch & 1) {
+ patch = (patch >> 1) ^ 0xedb88320L;
+ } else {
+ patch >>= 1;
+ }
+ if (a & 1) {
+ patch ^= 0x5b358fd3L;
+ }
+ a >>= 1;
+ }
+ patch ^= ~crc32(crc, buf, len - 4);
+ for (i = 0; i < 4; i++) {
+ buf[len - 4 + i] = patch & 0xff;
+ patch >>= 8;
+ }
+ /* Verify that we actually get the desired result */
+ crc = crc32(0L, Z_NULL, 0);
+ crc = crc32(crc, buf, len);
+ if (crc != dcrc) {
+ errx(1, "CRC patching is broken: wanted %08x, but got %08x.", dcrc, crc);
+ }
+}
+
+void
+usage() {
+ fprintf(stderr, "Usage:\n"
+ " jcgimage -o outputfile -u uImage [-v version]\n"
+ " jcgimage -o outputfile -k kernel -f rootfs [-v version]\n");
+ exit(1);
+}
+
+#define MODE_UNKNOWN 0
+#define MODE_UIMAGE 1
+#define MODE_KR 2
+
+/* The output image must not be larger than 4MiB - 5*64kiB */
+#define MAXSIZE (size_t)(4 * 1024 * 1024 - 5 * 64 * 1024)
+
+int
+main(int argc, char **argv)
+{
+ struct jcg_header *jh;
+ struct uimage_header *uh;
+ int c;
+ char *imagefile = NULL;
+ char *file1 = NULL;
+ char *file2 = NULL;
+ char *version = NULL;
+ int mode = MODE_UNKNOWN;
+ int fdo, fd1, fd2;
+ size_t size1, size2, sizeu, sizeo, off1, off2;
+ void *map;
+
+ /* Make sure the headers have the right size */
+ assert(sizeof(struct jcg_header) == 512);
+ assert(sizeof(struct uimage_header) == 64);
+
+ while ((c = getopt(argc, argv, "o:k:f:u:v:h")) != -1) {
+ switch (c) {
+ case 'o':
+ imagefile = optarg;
+ break;
+ case 'k':
+ if (mode == MODE_UIMAGE)
+ errx(1,"-k cannot be combined with -u");
+ mode = MODE_KR;
+ file1 = optarg;
+ break;
+ case 'f':
+ if (mode == MODE_UIMAGE)
+ errx(1,"-f cannot be combined with -u");
+ mode = MODE_KR;
+ file2 = optarg;
+ break;
+ case 'u':
+ if (mode == MODE_KR)
+ errx(1,"-u cannot be combined with -k and -r");
+ mode = MODE_UIMAGE;
+ file1 = optarg;
+ break;
+ case 'v':
+ version = optarg;
+ break;
+ case 'h':
+ default:
+ usage();
+ }
+ }
+ if (optind != argc) {
+ errx(1, "illegal arg \"%s\"", argv[optind]);
+ }
+ if (imagefile == NULL) {
+ errx(1, "no output file specified");
+ }
+ if (mode == MODE_UNKNOWN)
+ errx(1, "specify either -u or -k and -r");
+ if (mode == MODE_KR) {
+ if (file1 == NULL || file2 == NULL)
+ errx(1,"need -k and -r");
+ fd2 = opensize(file2, &size2);
+ }
+ fd1 = opensize(file1, &size1);
+ if (mode == MODE_UIMAGE) {
+ off1 = sizeof(*jh);
+ sizeu = size1 + 4;
+ sizeo = sizeof(*jh) + sizeu;
+ } else {
+ off1 = sizeof(*jh) + sizeof(*uh);
+ off2 = sizeof(*jh) + sizeof(*uh) + size1;
+ sizeu = sizeof(*uh) + size1 + size2;
+ sizeo = sizeof(*jh) + sizeu;
+ }
+
+ if (sizeo > MAXSIZE)
+ errx(1,"payload too large: %zd > %zd\n", sizeo, MAXSIZE);
+
+ fdo = open(imagefile, O_RDWR | O_CREAT | O_TRUNC, 00644);
+ if (fdo < 0)
+ err(1, "cannot open \"%s\"", imagefile);
+
+ if (ftruncate(fdo, sizeo) == -1) {
+ err(1, "cannot grow \"%s\" to %zd bytes", imagefile, sizeo);
+ }
+ map = mmap(NULL, sizeo, PROT_READ|PROT_WRITE, MAP_SHARED, fdo, 0);
+ uh = map + sizeof(*jh);
+ if (map == MAP_FAILED) {
+ err(1, "cannot mmap \"%s\"", imagefile);
+ }
+
+ if (read(fd1, map + off1, size1) != size1)
+ err(1, "cannot copy %s", file1);
+
+ if (mode == MODE_KR) {
+ if (read(fd2, map+off2, size2) != size2)
+ err(1, "cannot copy %s", file2);
+ mkuheader(uh, size1, size2);
+ } else if (mode == MODE_UIMAGE) {
+ craftcrc(ntohl(uh->ih_dcrc), (void*)uh + sizeof(*uh),
+ sizeu - sizeof(*uh));
+ }
+ mkjcgheader(map, sizeu, version);
+ munmap(map, sizeo);
+ close(fdo);
+ return 0;
+}
+
projects / openwrt.git / commitdiff