# Porting OpenWRT to a board with a supported SoC ## Intro Recently, some network devices caught my attention both on Aliexpress and Alibaba. Specifically, I found some interesting outdoor equipment for a very low price, ranging between 10-25$. * https://it.aliexpress.com/item/32964460654.html * https://it.aliexpress.com/item/4000091742124.html * https://www.alibaba.com/product-detail/AR9331-long-range-wifi-192-168_62106638650.html These are 2.4ghz AR9330 based boards, powered via POE (although on a non standard voltage), with two 10/100/1000 ethernet ports, an integrated antenna and a waterproof enclosure. I received the first one from Aliexpress but i plan to get some other to test as well. [There's a video on YouTube of someone unpacking and reviewing it](https://www.youtube.com/watch?v=i3WUmMOqit0). It also show the OEM web interface. ## Pictures ![Front](https://git.lsd.cat/g/openwrt-cpe46b/raw/master/images/front.jpg) ![Label](https://git.lsd.cat/g/openwrt-cpe46b/raw/master/images/label.jpg) ![Antenna](https://git.lsd.cat/g/openwrt-cpe46b/raw/master/images/antenna.jpg) ![PCB](https://git.lsd.cat/g/openwrt-cpe46b/raw/master/images/pcb.jpg) ## PCB From the PCB picture it is clear that the board has an easily accessible serial header and that it has a SOIC8 flash chip (Winbond 25Q64). Given this info, there are two possibilities to start learning about the board via hardware: connecting to the serial console and get whatever the oem firmware prints out and do a direct hardware image of the flash chip. ## Dumping firmware ### Dumping the original firmware without hardware Before even trying the SOIC clip or the serial port i wanted to check around the stock firmware. It looks like the device has no DHCP server but it has a fixed `192.168.0.1` ip address and default `admin:admin` credentials. By default, there's only the web intrace and a telnet server listening on the public interface. The credentials for the telnet interface are `root` without password. ``` CPE46B mips #1 Thu Sep 5 18:02:48 CST 2019 (none) CPE46B login: root Ziking logintalk start ................... Interactive mode > help help :Show this usage help art.sh :Run art server get_log :Download log from ap to remote. Usage: get_log [remote ip] ifconfig :Network configuration commands ip :Network configuration commands iwconfig :Wlan configuration commands iwpriv :Wlan configuration commands iwlist :Wlan configuration commands oem :Change/Show MAC address & sn; Usage: oem get/set ping :Command ping ps :Command ps route :Network configuration commands sendAT :Send AT command for lte device show_oem :Show OEM infomation show_ver :Show AP software version tc :Qos configuration commands top :Command top wlanconfig :Athreos wlan configuration commands T1 :Test 5G RF with 20M bandwidth T2 :Test 5G RF with 40M bandwidth T3 :Test 2.4G RF with 20M bandwidth T4 :Test 2.4G RF with 40M bandwidth T5 :Test upload.Usage: T5 [remote ip] T6 :Test download.Usage: T6 > ``` While upon collecting the user is dropped in a restriced pompt with few commands available, it is possible to inject commands in almost any of it via common shell separators `|;&`. With the command injection is easy to understand that the device is already running a heavily customized OpenWRT fork, running on `Linux 2.6.31`. ``` > iwconfig|uname -a lo no wireless extensions. eth0 no wireless extensions. eth1 no wireless extensions. wifi0 no wireless extensions. br0 no wireless extensions. Linux CPE46B 2.6.31--LSDK-9.2.0_U9.915 #1 Thu Sep 5 18:02:48 CST 2019 mips GNU/Linux ``` Catting `/proc/mtd` gives more info about flash layout. ``` > iwconfig|cat /proc/mtd dev: size erasesize name mtd0: 00010000 00010000 "u-boot" mtd1: 00010000 00010000 "u-boot-env" mtd2: 00360000 00010000 "rootfs" mtd3: 00100000 00010000 "uImage" mtd4: 00360000 00010000 "rootfs1" mtd5: 00010000 00010000 "NVRAM" mtd6: 00010000 00010000 "ART" ``` And `/proc/cpuinfo` about the SoC and the CPU. ``` > iwconfig|cat /proc/cpuinfo system type : Atheros AR9330 (Hornet) processor : 0 cpu model : MIPS 24Kc V7.4 BogoMIPS : 266.24 wait instruction : yes microsecond timers : yes tlb_entries : 16 extra interrupt vector : yes hardware watchpoint : yes, count: 4, address/irw mask: [0x0000, 0x0020, 0x0020, 0x0588] ASEs implemented : mips16 shadow register sets : 1 core : 0 VCED exceptions : not available VCEI exceptions : not available ``` By knowing the size of each mtd partition, we get to know that it has a 8M flash chip. This makes sense given that the chip has written on it `25Q64`, where `64` is the size in Megabits. Using `dd` it is possible to dump each partition, download it and even reasseble the full firmware image simply with `cat` afterwards. for X in 0..6 ``` > iwconfig|dd if=/dev/mtd0 of=/var/tmp/web/mtdX ``` for X in 0..6 ``` # wget http://192.168.0.1/mtdX ``` ``` # cat mtd0 mtd1 mtd2 mtd3 mtd4 mtd5 mtd6 > flash.bin ``` ``` # ls -lart flash.bin -rwxrwxrwx 1 user user 8388608 Apr 12 12:40 flash.bin ``` Where `8388608/1024=8192K`. When the device boots up, a lot of custom scripts and services will run. The most custom part of the firmware, which means the web interface and their custom binaries are somehow encrypted or more simply obfuscated and loaded at runtime in ram. At rest, the obfuscated files are called `/usr/web.bin`, `/usr/sbin.bin`, `/usr/apps.bin`. The executable responsabile for decrypting them to more simpler `tgz` archives is called `ap_monitor`. Ghidra sucessfully decompile this binary and the obfuscation mechanism is not very complicated and could reversed with not too much effort but there's proably no reason to do so. Since I was unable to find the manufacturer both on the package or anywhere else, i'll refer to it as `ZiKing` as it seems that's the name stated in their own proprietary config file. On Aliexpress, the same device is also often said to be made by `ANDDEAR`. Both do not seem to have any presence on the English internet. ``` FID="OEM" FLASH_ID="SPI" PCB="v1.0" PN="CPE46B" PT="AP" VER="4.3.7" VER1="4.3.7" RF_MODE="1T1R" WAN="0" EXT_PA="1" TRSW="1" SERVER_DOMAIN="www.ziking.net" DHCPD_EVER="0" IANA="37260" MAXNUM=4 ####language CSS_STYLE="SHX46B" LANG="en" SUPPORT_LANG="en,zh" COUNTRYCODE="76" SUPPORT_COUNTRYCODE="76,156,276,392" ####radio & vaps MAX_VAPS="8" MAX_RFS="1" #0: auto, 1:2.4G, 2-5.8G RF0_SUPPORT_FREQ="1" #RF1_SUPPORT_FREQ="0" SUPPORT_AUTO_ACTIVE="0" #### product Type ###0: FIT AP mode ###1: WIFI CPE mode ###2: LTE/3G CPE mode ###3: Route mode ####for UPNP MANUFACTURER="XIAN ZIKING NETWORK COMMUNICATIONS CO.,LTD." MANUFACTURERURL="http://www.ziking.net" MODELDESCRIPTION="Wireless Broadband Access Point / CPE" #### PRODUCT_TYPE="1" SUPPORT_PRODUCT_TYPE="2,3" SUPPORT_WAN_MODE="251" SUPPORT_AUTH_MODE="63" SUPPORT_WLAN_MODE="7" SUPPORT_MAC_MAP="0" PRODUCT_ID="0" APSYSNEID="SYSNEIDatleast16chars1234567890123456" AP_NASID="NASIDatleast16chars1234567890123456" APSYSHOSTNAME="APNAMEatleast40chars1234567890123456789012345678901234567890" AP_LOCATION="shenzhen" AP_COVERAGETYPE="2" AP_DESCRIPRION="Customer Premise Equipment" AP_SOFT_VERDOR="ZiKing" AP_ORIG_VENDOR="ZiKing" AP_CPU="ar9331" CPU_SPEED="400000000" #it must be xxMB(type) AP_MEMORY="64MB(S29GL064M)" AP_FLASH="8MB(HY57V561620TP-H)" #max power, dbm AP_MAX_POWER="15" PCB0="SX933146B" BUS="AHB" SUPPORT_AC_CURL_MGR="0" AP_SERIALNUMBER=001122334455 ``` Note that the `64M` RAM value written there is wrong. This one has `32M` but it probably depends on the production batch. The only thing actually existing, given that as of now the website shows a default page, is [their IANA assignment number](https://oidref.com/1.3.6.1.4.1.37260). ### Raspberry PI GPIO with a SOIC8 CLIP ![Soic](https://git.lsd.cat/g/openwrt-cpe46b/raw/master/images/soic.jpg) [The following istruction are recycled from this other guide](https://git.lsd.cat/g/thinkpad-coreboot-qubes/src/master/README.md). ``` ______ 1--| O |--8 2--| |--7 3--| |--6 4--|______|--5 ``` Remeber to research your chip model and manufacturer and double check the pin layout using the official datasheet. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | Flash pin number | |----|----|-----|-----|----|-----|-------|-----|------------------| | CS | DO | /WP | GND | DI | CLK | /HOLD | VCC | Pin name | | 24 | 21 | GND | 25 | 19 | 23 | GND | 17 | Rpi GPIO number | Please refer to the multiple flashing guides available * https://www.flashrom.org/RaspberryPi * https://libreboot.org/docs/install/rpi_setup.html * https://karlcordes.com/coreboot-x220/ * https://tylercipriani.com/blog/2016/11/13/coreboot-on-the-thinkpad-x220-with-a-raspberry-pi/ * https://github.com/bibanon/Coreboot-ThinkPads/wiki/Hardware-Flashing-with-Raspberry-Pi From a root prompt on the Rpi ``` # flashrom -p linux_spi:dev=/dev/spidev0.0,spispeed=1000 -r flash1.bin # flashrom -p linux_spi:dev=/dev/spidev0.0,spispeed=1000 -r flash2.bin # flashrom -p linux_spi:dev=/dev/spidev0.0,spispeed=1000 -r flash3.bin # sha1sum flash*.bin ``` Check that all the checksums do match. In case they don't there's probably something wrong in the clip position or in the wiring. Remember that no pin should left floating even if it's not useful for the operation. /WP and /HOLD should be always connected to something like GND or VCC. ### Serial interface ![Serial](https://git.lsd.cat/g/openwrt-cpe46b/raw/master/images/serial.jpg) The serial header is easy to work with and has clearly written the pinout on it. Any cheap usb adapter will probably work. In my case the baudrate is 115200, however, a script like [baudare.py](https://github.com/somu1795/baudrate) should do the trick. Common softwares for serial communication are `minicom` and `screen`. ``` # screen /dev/ttyUSB0 115200 ``` ## Porting ### Partition layout The info learnet from `proc/mtd` are extremely useful. * `mtd0 u-boot` is a 64K partition which contains the u-boot bootloader * `mtd1 u-boot-env` is a 64K partition containing the u-boot configuration * `mtd2 rootfs` is a jffs2 partition containing the actual image * `mtd3 uImage` is a squashfs kernel image * `mtd4 rootfs1` is a jffs2 partition containing a secondary image, probably used for recovery * `mtd5 NVRAM` is a 64K partition which contains a `tgz` for OEM system configuration files * `mtd6 ART` is a 64K partition [that contains calibration data for the radio chip](https://github.com/pepe2k/ar9300_eeprom) The total size is of course 8192K. The partitions are not partitions in an EXT or NTFS sense. The data is just contiguos on the flash but the bootloader and the kernel are responsible for considering the different regions separate. That's the reason because `cat` works and it is so simple to work with them. Since for vanilla OpenWRT a custom partition for configuration is not needed, and two rootfs aren't useful and everything can be packed in a single partition with more space for packages and user data our target could be: * `mtd0 u-boot` oeiginal image * `mtd1 u-boot-env` some values here needs to be modified * `mtd2 firmware` 8000K OpenWRT partition (`firmware` is the standard OpenWRT naming) * `mtd3 ART` original image On some other devices this is not needed because maybe the partition layout already makes sense: ie there's already a single partition with kernel and data. They are a bit easier to play with because in that case there's probably no need to manipulate the boot environment. Furthermore, in this case, building an image for flashing trough the OEM web interface might be not possible. ### U-Boot U-boot is an Open Source Bootloader mainly for embedded devices. While it is actively developed, the actual version depends on the SDK a vendor provides for its SoC. Atheros, for `ar9330` seems to have used 1.4 as base, which is almost a decade old. Here's the u-boot log from the serial interface: ``` U-Boot 1.1.413 (Aug 29 2012 - 10:36:47) AP121-2MB (ar9330) U-boot DRAM: 32 MB flash size 8388608, sector count = 128 Flash: 8 MB In: serial Out: serial Err: serial Net: eth0: c8:ee:a6:3f:62:ad eth0 up eth1: 00:0a:0b:0c:0d:0e eth1 up eth0, eth1 Hit any key to stop autoboot: 0 ## Booting image at 9f380000 ... Image Name: Linux Kernel Image Created: 2019-09-05 10:02:56 UTC Image Type: MIPS Linux Kernel Image (lzma compressed) Data Size: 864262 Bytes = 844 kB Load Address: 80002000 Entry Point: 801d0de0 Verifying Checksum at 0x9f380040 ...OK Uncompressing Kernel Image ... OK No initrd ## Transferring control to Linux (at address 801d0de0) ... ## Giving linux memsize in bytes, 33554432 Starting kernel ... Booting AR9330(Hornet)... init started: BusyBox v1.15.0 (2019-09-05 18:04:35 CST) starting pid 19, tty '': '/etc/rc.d/rcS' Isking Copyright 2016.... Not support pin simple config Not found /etc/rc.d/rc.getethdev Not found /etc/rc.d/rc.fs load driver adf loaded sucessfully asf loaded sucessfully ath_hal loaded sucessfully ath_rate_atheros loaded sucessfully ath_dev loaded sucessfully umac loaded sucessfully 2 starting pid 301, tty '': '/bin/getty ttyS0 115200' CPE46B mips #1 Thu Sep 5 18:02:48 CST 2019 (none) CPE46B login: ``` This confirms most of what we have got to know from the OEM firmware, 8M flash, 32M RAM, AR9330 SoC. Hornet is the codename for a [specific ALFA board](https://openwrt.org/toh/alfa_network/hornet-ub), and probably its target has been recycled for this U-Boot build. U-Boot has the possibility to drop the user to an interactive command prompt if a key is hit on the early boot phase: ``` U-Boot 1.1.413 (Aug 29 2012 - 10:36:47) AP121-2MB (ar9330) U-boot DRAM: 32 MB flash size 8388608, sector count = 128 Flash: 8 MB In: serial Out: serial Err: serial Net: eth0: c8:ee:a6:3f:62:ad eth0 up eth1: 00:0a:0b:0c:0d:0e eth1 up eth0, eth1 Hit any key to stop autoboot: 0 ar7240> help padfix - fixed uboot bug ? - alias for 'help' bdinfo - print Board Info structure boot - boot default, i.e., run 'bootcmd' bootd - boot default, i.e., run 'bootcmd' bootm - boot application image from memory cp - memory copy erase - erase FLASH memory help - print online help loadb - load binary file over serial line (kermit mode) loads - load S-Record file over serial line loady - load binary file over serial line (ymodem mode) md - memory display mm - memory modify (auto-incrementing) mw - memory write (fill) ping - send ICMP ECHO_REQUEST to network host printenv- print environment variables progmac - Set ethernet MAC addresses protect - enable or disable FLASH write protection reset - Perform RESET of the CPU run - run commands in an environment variable saveenv - save environment variables to persistent storage setenv - set environment variables tftpboot- boot image via network using TFTP protocol version - print monitor version wd - check and set watchdog ar7240> ``` _Note: `ar7240>` is probably there just because someone forgot to edit the prompt to the correct chipset name. It's just a static name and it is irrelevant.