+++ /dev/null
-Linux is now one of the most widespread operating system for embedded devices due
-to its openess as well as the wide variety of platforms it can run on. Many
-manufacturer actually use it in firmware you can find on many devices: DVB-T
-decoders, routers, print servers, DVD players ... Most of the time the stock
-firmware is not really open to the consumer, even if it uses open source software.
-
-You might be interested in running a Linux based firmware for your router for
-various reasons: extending the use of a network protocol (such as IPv6), having
-new features, new piece of software inside, or for security reasons. A fully
-open-source firmware is de-facto needed for such applications, since you want to
-be free to use this or that version of a particular reason, be able to correct a
-particular bug. Few manufacturers do ship their routers with a Sample Development Kit,
-that would allow you to create your own and custom firmware and most of the time,
-when they do, you will most likely not be able to complete the firmware creation process.
-
-This is one of the reasons why OpenWrt and other firmware exists: providing a
-version independent, and tools independent firmware, that can be run on various
-platforms, known to be running Linux originally.
-
-\subsection{Which Operating System does this device run?}
-
-There is a lot of methods to ensure your device is running Linux. Some of them do
-need your router to be unscrewed and open, some can be done by probing the device
-using its external network interfaces.
-
-\subsubsection{Operating System fingerprinting and port scanning}
-
-A large bunch of tools over the Internet exists in order to let you do OS
-fingerprinting, we will show here an example using \textbf{nmap}:
-
-\begin{Verbatim}
-nmap -P0 -O <IP address>
-Starting Nmap 4.20 ( http://insecure.org ) at 2007-01-08 11:05 CET
-Interesting ports on 192.168.2.1:
-Not shown: 1693 closed ports
-PORT STATE SERVICE
-22/tcp open ssh
-23/tcp open telnet
-53/tcp open domain
-80/tcp open http
-MAC Address: 00:13:xx:xx:xx:xx (Cisco-Linksys)
-Device type: broadband router
-Running: Linksys embedded
-OS details: Linksys WRT54GS v4 running OpenWrt w/Linux kernel 2.4.30
-Network Distance: 1 hop
-\end{Verbatim}
-
-nmap is able to report whether your device uses a Linux TCP/IP stack, and if so,
-will show you which Linux kernel version is probably runs. This report is quite
-reliable and it can make the distinction between BSD and Linux TCP/IP stacks and others.
-
-Using the same tool, you can also do port scanning and service version discovery.
-For instance, the following command will report which IP-based services are running
-on the device, and which version of the service is being used:
-
-\begin{verbatim}
-nmap -P0 -sV <IP address>
-Starting Nmap 4.20 ( http://insecure.org ) at 2007-01-08 11:06 CET
-Interesting ports on 192.168.2.1:
-Not shown: 1693 closed ports
-PORT STATE SERVICE VERSION
-22/tcp open ssh Dropbear sshd 0.48 (protocol 2.0)
-23/tcp open telnet Busybox telnetd
-53/tcp open domain ISC Bind dnsmasq-2.35
-80/tcp open http OpenWrt BusyBox httpd
-MAC Address: 00:13:xx:xx:xx:xx (Cisco-Linksys)
-Service Info: Device: WAP
-\end{verbatim}
-
-The web server version, if identified, can be determining in knowing the Operating
-System. For instance, the \textbf{BOA} web server is typical from devices running
-an open-source Unix or Unix-like.
-
-\subsubsection{Wireless Communications Fingerprinting}
-
-Although this method is not really known and widespread, using a wireless scanner
-to discover which OS your router or Access Point run can be used. We do not have
-a clear example of how this could be achieved, but you will have to monitor raw
-802.11 frames and compare them to a very similar device running a Linux based firmware.
-
-\subsubsection{Web server security exploits}
-
-The Linksys WRT54G was originally hacked by using a "ping bug" discovered in the
-web interface. This tip has not been fixed for months by Linksys, allowing people
-to enable the "boot\_wait" helper process via the web interface. Many web servers
-used in firmwares are open source web server, thus allowing the code to be audited
-to find an exploit. Once you know the web server version that runs on your device,
-by using \textbf{nmap -sV} or so, you might be interested in using exploits to reach
-shell access on your device.
-
-\subsubsection{Native Telnet/SSH access}
-
-Some firmwares might have restricted or unrestricted Telnet/SSH access, if so,
-try to log in with the web interface login/password and see if you can type in
-some commands. This is actually the case for some Broadcom BCM963xx based firmwares
-such as the one in Neuf/Cegetel ISP routers, Club-Internet ISP CI-Box and many
-others. Some commands, like \textbf{cat} might be left here and be used to
-determine the Linux kernel version.
-
-\subsubsection{Analysing a binary firmware image}
-
-You are very likely to find a firmware binary image on the manufacturer website,
-even if your device runs a proprietary operating system. If so, you can download
-it and use an hexadecimal editor to find printable words such as \textbf{vmlinux},
-\textbf{linux}, \textbf{ramdisk}, \textbf{mtd} and others.
-
-Some Unix tools like \textbf{hexdump} or \textbf{strings} can be used to analyse
-the firmware. Below there is an example with a binary firmware found other the Internet:
-
-\begin{verbatim}
-hexdump -C <binary image.extension> | less (more)
-00000000 46 49 52 45 32 2e 35 2e 30 00 00 00 00 00 00 00 |FIRE2.5.0.......|
-00000010 00 00 00 00 31 2e 30 2e 30 00 00 00 00 00 00 00 |....1.0.0.......|
-00000020 00 00 00 00 00 00 00 38 00 43 36 29 00 0a e6 dc |.......8.C6)..??|
-00000030 54 49 44 45 92 89 54 66 1f 8b 08 08 f8 10 68 42 |TIDE..Tf....?.hB|
-00000040 02 03 72 61 6d 64 69 73 6b 00 ec 7d 09 bc d5 d3 |..ramdisk.?}.???|
-00000050 da ff f3 9b f7 39 7b ef 73 f6 19 3b 53 67 ea 44 |???.?9{?s?.;Sg?D|
-\end{verbatim}
-
-Scroll over the firmware to find printable words that can be significant.
-
-\subsubsection{Amount of flash memory}
-
-Linux can hardly fit in a 2MB flash device, once you have opened the device and
-located the flash chip, try to find its characteristics on the Internet. If
-your flash chip is a 2MB or less device, your device is most likely to run a
-proprietary OS such as WindRiver VxWorks, or a custom manufacturer OS like Zyxel ZynOS.
-
-OpenWrt does not currently run on devices which have 2MB or less of flash memory.
-This limitation will probably not be worked around since those devices are most
-of the time micro-routers, or Wireless Access Points, which are not the main
-OpenWrt target.
-
-\subsubsection{Pluging a serial port}
-
-By using a serial port and a level shifter, you may reach the console that is being shown by the device
-for debugging or flashing purposes. By analysing the output of this device, you can
-easily notice if the device uses a Linux kernel or something different.
-
-\subsection{Finding and using the manufacturer SDK}
-
-Once you are sure your device run a Linux based firmware, you will be able to start
-hacking on it. If the manufacturer respected the GPL, it will have released a Sample
-Development Kit with the device.
-
-\subsubsection{GPL violations}
-
-Some manufacturers do release a Linux based binary firmware, with no sources at all.
-The first step before doing anything is to read the license coming with your device,
-then write them about this lack of Open Source code. If the manufacturer answers
-you they do not have to release a SDK containing Open Source software, then we
-recommend you get in touch with the gpl-violations.org community.
-
-You will find below a sample letter that can be sent to the manufacturer:
-
-\begin{verse}
-Miss, Mister,
-
-I am using a <device name>, and I cannot find neither on your website nor on the
-CD-ROM the open source software used to build or modify the firmware.
-
-In conformance to the GPL license, you have to release the following sources:
-
-\begin{itemize}
-\item complete toolchain that made the kernel and applications be compiled (gcc, binutils, libc)
-\item tools to build a custom firmware (mksquashfs, mkcramfs ...)
-\item kernel sources with patches to make it run on this specific hardware, this does not include binary drivers
-\end{itemize}
-
-Thank you very much in advance for your answer.
-
-Best regards, <your name>
-\end{verse}
-
-\subsubsection{Using the SDK}
-
-Once the SDK is available, you are most likely not to be able to build a complete
-or functional firmware using it, but parts of it, like only the kernel, or only
-the root filesystem. Most manufacturers do not really care releasing a tool that
-do work every time you uncompress and use it.
-
-You should anyway be able to use the following components:
-
-\begin{itemize}
-\item kernel sources with more or less functional patches for your hardware
-\item binary drivers linked or to be linked with the shipped kernel version
-\item packages of the toolchain used to compile the whole firmware: gcc, binutils, libc or uClibc
-\item binary tools to create a valid firmware image
-\end{itemize}
-
-Your work can be divided into the following tasks:
-
-\begin{itemize}
-\item create a clean patch of the hardware specific part of the linux kernel
-\item spot potential kernel GPL violations especially on netfilter and USB stack stuff
-\item make the binary drivers work, until there are open source drivers
-\item use standard a GNU toolchain to make working executables
-\item understand and write open source tools to generate a valid firmware image
-\end{itemize}
-
-\subsubsection{Creating a hardware specific kernel patch}
-
-Most of the time, the kernel source that comes along with the SDK is not really
-clean, and is not a standard Linux version, it also has architecture specific
-fixes backported from the \textbf{CVS} or the \textbf{git} repository of the
-kernel development trees. Anyway, some parts can be easily isolated and used as
-a good start to make a vanilla kernel work your hardware.
-
-Some directories are very likely to have local modifications needed to make your
-hardware be recognized and used under Linux. First of all, you need to find out
-the linux kernel version that is used by your hardware, this can be found by
-editing the \textbf{linux/Makefile} file.
-
-\begin{verbatim}
-head -5 linux-2.x.x/Makefile
-VERSION = 2
-PATCHLEVEL = x
-SUBLEVEL = y
-EXTRAVERSION = z
-NAME=A fancy name
-\end{verbatim}
-
-So now, you know that you have to download a standard kernel tarball at
-\textbf{kernel.org} that matches the version being used by your hardware.
-
-Then you can create a \textbf{diff} file between the two trees, especially for the
-following directories:
-
-\begin{verbatim}
-diff -urN linux-2.x.x/arch/<sub architecture> linux-2.x.x-modified/arch/<sub architecture> > 01-architecture.patch
-diff -urN linux-2.x.x/include/ linux-2.x.x-modified/include > 02-includes.patch
-diff -urN linux-2.x.x/drivers/ linux-2.x.x-modified/drivers > 03-drivers.patch
-\end{verbatim}
-
-This will constitute a basic set of three patches that are very likely to contain
-any needed modifications that has been made to the stock Linux kernel to run on
-your specific device. Of course, the content produced by the \textbf{diff -urN}
-may not always be relevant, so that you have to clean up those patches to only
-let the "must have" code into them.
-
-The first patch will contain all the code that is needed by the board to be
-initialized at startup, as well as processor detection and other boot time
-specific fixes.
-
-The second patch will contain all useful definitions for that board: addresses,
-kernel granularity, redefinitions, processor family and features ...
-
-The third patch may contain drivers for: serial console, ethernet NIC, wireless
-NIC, USB NIC ... Most of the time this patch contains nothing else than "glue"
-code that has been added to make the binary driver work with the Linux kernel.
-This code might not be useful if you plan on writing drivers from scratch for
-this hardware.
-
-\subsubsection{Using the device bootloader}
-
-The bootloader is the first program that is started right after your device has
-been powered on. This program, can be more or less sophisticated, some do let you
-do network booting, USB mass storage booting ... The bootloader is device and
-architecture specific, some bootloaders were designed to be universal such as
-RedBoot or U-Boot so that you can meet those loaders on totally different
-platforms and expect them to behave the same way.
-
-If your device runs a proprietary operating system, you are very likely to deal
-with a proprietary boot loader as well. This may not always be a limitation,
-some proprietary bootloaders can even have source code available (i.e : Broadcom CFE).
-
-According to the bootloader features, hacking on the device will be more or less
-easier. It is very probable that the bootloader, even exotic and rare, has a
-documentation somewhere over the Internet. In order to know what will be possible
-with your bootloader and the way you are going to hack the device, look over the
-following features :
-
-\begin{itemize}
-\item does the bootloader allow net booting via bootp/DHCP/NFS or tftp
-\item does the bootloader accept loading ELF binaries ?
-\item does the bootloader have a kernel/firmware size limitation ?
-\item does the bootloader expect a firmware format to be loaded with ?
-\item are the loaded files executed from RAM or flash ?
-\end{itemize}
-
-Net booting is something very convenient, because you will only have to set up network
-booting servers on your development station, and keep the original firmware on the device
-till you are sure you can replace it. This also prevents your device from being flashed,
-and potentially bricked every time you want to test a modification on the kernel/filesystem.
-
-If your device needs to be flashed every time you load a firmware, the bootlader might
-only accept a specific firmware format to be loaded, so that you will have to
-understand the firmware format as well.
-
-\subsubsection{Making binary drivers work}
-
-As we have explained before, manufacturers do release binary drivers in their GPL
-tarball. When those drivers are statically linked into the kernel, they become GPL
-as well, fortunately or unfortunately, most of the drivers are not statically linked.
-This anyway lets you a chance to dynamically link the driver with the current kernel
-version, and try to make them work together.
-
-This is one of the most tricky and grey part of the fully open source projects.
-Some drivers require few modifications to be working with your custom kernel,
-because they worked with an earlier kernel, and few modifications have been made
-to the kernel in-between those versions. This is for instance the case with the
-binary driver of the Broadcom BCM43xx Wireless Chipsets, where only few differences
-were made to the network interface structures.
-
-Some general principles can be applied no matter which kernel version is used in
-order to make binary drivers work with your custom kernel:
-
-\begin{itemize}
-\item turn on kernel debugging features such as:
-\begin{itemize}
-\item CONFIG\_DEBUG\_KERNEL
-\item CONFIG\_DETECT\_SOFTLOCKUP
-\item CONFIG\_DEBUG\_KOBJECT
-\item CONFIG\_KALLSYMS
-\item CONFIG\_KALLSYMS\_ALL
-\end{itemize}
-\item link binary drivers when possible to the current kernel version
-\item try to load those binary drivers
-\item catch the lockups and understand them
-\end{itemize}
-
-Most of the time, loading binary drivers will fail, and generate a kernel oops.
-You can know the last symbol the binary drivers attempted to use, and see in the
-kernel headers file, if you do not have to move some structures field before or
-after that symbol in order to keep compatibily with both the binary driver and
-the stock kernel drivers.
-
-\subsubsection{Understanding the firmware format}
-
-You might want to understand the firmware format, even if you are not yet capable
-of running a custom firmware on your device, because this is sometimes a blocking
-part of the flashing process.
-
-A firmware format is most of the time composed of the following fields:
-
-\begin{itemize}
-\item header, containing a firmware version and additional fields: Vendor, Hardware version ...
-\item CRC32 checksum on either the whole file or just part of it
-\item Binary and/or compressed kernel image
-\item Binary and/or compressed root filesystem image
-\item potential garbage
-\end{itemize}
-
-Once you have figured out how the firmware format is partitioned, you will have
-to write your own tool that produces valid firmware binaries. One thing to be very
-careful here is the endianness of either the machine that produces the binary
-firmware and the device that will be flashed using this binary firmware.
-
-\subsubsection{Writing a flash map driver}
-
-The flash map driver has an important role in making your custom firmware work
-because it is responsible of mapping the correct flash regions and associated
-rights to specific parts of the system such as: bootloader, kernel, user filesystem.
-
-Writing your own flash map driver is not really a hard task once you know how your
-firmware image and flash is structured. You will find below a commented example
-that covers the case of the device where the bootloader can pass to the kernel its partition plan.
-
-First of all, you need to make your flash map driver be visible in the kernel
-configuration options, this can be done by editing the file \
-\textbf{linux/drivers/mtd/maps/Kconfig}:
-
-\begin{verbatim}
-config MTD_DEVICE_FLASH
- tristate "Device Flash device"
- depends on ARCHITECTURE && DEVICE
- help
- Flash memory access on DEVICE boards. Currently only works with
- Bootloader Foo and Bootloader Bar.
-\end{verbatim}
-
-Then add your source file to the \textbf{linux/drivers/mtd/maps/Makefile}, so
-that it will be compiled along with the kernel.
-
-\begin{verbatim}
-obj-\$(CONFIG_MTD_DEVICE_FLASH) += device-flash.o
-\end{verbatim}
-
-You can then write the kernel driver itself, by creating a
-\textbf{linux/drivers/mtd/maps/device-flash.c} C source file.
-
-\begin{verbatim}
-// Includes that are required for the flash map driver to know of the prototypes:
-#include <asm/io.h>
-#include <linux/init.h>
-#include <linux/kernel.h>
-#include <linux/mtd/map.h>
-#include <linux/mtd/mtd.h>
-#include <linux/mtd/partitions.h>
-#include <linux/vmalloc.h>
-
-// Put some flash map definitions here:
-#define WINDOW_ADDR 0x1FC00000 /* Real address of the flash */
-#define WINDOW_SIZE 0x400000 /* Size of flash */
-#define BUSWIDTH 2 /* Buswidth */
-
-static void __exit device_mtd_cleanup(void);
-
-static struct mtd_info *device_mtd_info;
-
-static struct map_info devicd_map = {
- .name = "device",
- .size = WINDOW_SIZE,
- .bankwidth = BUSWIDTH,
- .phys = WINDOW_ADDR,
-};
-
-static int __init device_mtd_init(void)
-{
- // Display that we found a flash map device
- printk("device: 0x\%08x at 0x\%08x\n", WINDOW_SIZE, WINDOW_ADDR);
- // Remap the device address to a kernel address
- device_map.virt = ioremap(WINDOW_ADDR, WINDOW_SIZE);
-
- // If impossible to remap, exit with the EIO error
- if (!device_map.virt) {
- printk("device: Failed to ioremap\n");
- return -EIO;
- }
-
- // Initialize the device map
- simple_map_init(&device_map);
-
- /* MTD informations are closely linked to the flash map device
- you might also use "jedec_probe" "amd_probe" or "intel_probe" */
- device_mtd_info = do_map_probe("cfi_probe", &device_map);
-
- if (device_mtd_info) {
- device_mtd_info->owner = THIS_MODULE;
-
- int parsed_nr_parts = 0;
-
- // We try here to use the partition schema provided by the bootloader specific code
- if (parsed_nr_parts == 0) {
- int ret = parse_bootloader_partitions(device_mtd_info, &parsed_parts, 0);
- if (ret > 0) {
- part_type = "BootLoader";
- parsed_nr_parts = ret;
- }
- }
-
- add_mtd_partitions(devicd_mtd_info, parsed_parts, parsed_nr_parts);
-
- return 0;
- }
- iounmap(device_map.virt);
-
- return -ENXIO;
-}
-
-// This function will make the driver clean up the MTD device mapping
-static void __exit device_mtd_cleanup(void)
-{
- // If we found a MTD device before
- if (device_mtd_info) {
- // Delete every partitions
- del_mtd_partitions(device_mtd_info);
- // Delete the associated map
- map_destroy(device_mtd_info);
- }
-
- // If the virtual address is already in use
- if (device_map.virt) {
- // Unmap the physical address to a kernel space address
- iounmap(device_map.virt);
- // Reset the structure field
- device_map.virt = 0;
- }
-}
-
-
-// Macros that indicate which function is called on loading/unloading the module
-module_init(device_mtd_init);
-module_exit(device_mtd_cleanup);
-
-
-// Macros defining license and author, parameters can be defined here too.
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Me, myself and I <memyselfandi@domain.tld");
-\end{verbatim}
-
-\subsection{Adding your target in OpenWrt}
-
-Once you spotted the key changes that were made to the Linux kernel
-to support your target, you will want to create a target in OpenWrt
-for your hardware. This can be useful to benefit from the toolchain
-that OpenWrt builds as well as the resulting user-space and kernel
-configuration options.
-
-Provided that your target is already known to OpenWrt, it will be
-as simple as creating a \texttt{target/linux/board} directory
-where you will be creating the following directories and files.
-
-Here for example, is a \texttt{target/linux/board/Makefile}:
-
-\begin{Verbatim}[frame=single,numbers=left]
-#
-# Copyright (C) 2009 OpenWrt.org
-#
-# This is free software, licensed under the GNU General Public License v2.
-# See /LICENSE for more information.
-#
-include $(TOPDIR)/rules.mk
-
-ARCH:=mips
-BOARD:=board
-BOARDNAME:=Eval board
-FEATURES:=squashfs jffs2 pci usb
-
-LINUX_VERSION:=2.6.27.10
-
-include $(INCLUDE_DIR)/target.mk
-
-DEFAULT_PACKAGES += hostapd-mini
-
-define Target/Description
- Build firmware images for Evaluation board
-endef
-
-$(eval $(call BuildTarget))
-\end{Verbatim}
-
-\begin{itemize}
- \item \texttt{ARCH} \\
- The name of the architecture known by Linux and uClibc
- \item \texttt{BOARD} \\
- The name of your board that will be used as a package and build directory identifier
- \item \texttt{BOARDNAME} \\
- Expanded name that will appear in menuconfig
- \item \texttt{FEATURES} \\
- Set of features to build filesystem images, USB, PCI, VIDEO kernel support
- \item \texttt{LINUX\_VERSION} \\
- Linux kernel version to use for this target
- \item \texttt{DEFAULT\_PACKAGES} \\
- Set of packages to be built by default
-\end{itemize}
-
-A partial kernel configuration which is either named \texttt{config-default} or which matches the kernel version \texttt{config-2.6.x} should be present in \texttt{target/linux/board/}.
-This kernel configuration will only contain the relevant symbols to support your target and can be changed using \texttt{make kernel\_menuconfig}.
-
-To patch the kernel sources with the patches required to support your hardware, you will have to drop them in \texttt{patches} or in \texttt{patches-2.6.x} if there are specific
-changes between kernel versions. Additionnaly, if you want to avoid creating a patch that will create files, you can put those files into \texttt{files} or \texttt{files-2.6.x}
-with the same directory structure that the kernel uses (e.g: drivers/mtd/maps, arch/mips ..).
-
-The build system will require you to create a \texttt{target/linux/board/image/Makefile}:
-
-\begin{Verbatim}[frame=single,numbers=left]
-#
-# Copyright (C) 2009 OpenWrt.org
-#
-# This is free software, licensed under the GNU General Public License v2.
-# See /LICENSE for more information.
-#
-include $(TOPDIR)/rules.mk
-include $(INCLUDE_DIR)/image.mk
-
-define Image/BuildKernel
- cp $(KDIR)/vmlinux.elf $(BIN_DIR)/openwrt-$(BOARD)-vmlinux.elf
- gzip -9n -c $(KDIR)/vmlinux > $(KDIR)/vmlinux.bin.gz
- $(STAGING_DIR_HOST)/bin/lzma e $(KDIR)/vmlinux $(KDIR)/vmlinux.bin.l7
- dd if=$(KDIR)/vmlinux.bin.l7 of=$(BIN_DIR)/openwrt-$(BOARD)-vmlinux.lzma bs=65536 conv=sync
- dd if=$(KDIR)/vmlinux.bin.gz of=$(BIN_DIR)/openwrt-$(BOARD)-vmlinux.gz bs=65536 conv=sync
-endef
-
-define Image/Build/squashfs
- $(call prepare_generic_squashfs,$(KDIR)/root.squashfs)
-endef
-
-define Image/Build
- $(call Image/Build/$(1))
- dd if=$(KDIR)/root.$(1) of=$(BIN_DIR)/openwrt-$(BOARD)-root.$(1) bs=128k conv=sync
-
- -$(STAGING_DIR_HOST)/bin/mkfwimage \
- -B XS2 -v XS2.ar2316.OpenWrt \
- -k $(BIN_DIR)/openwrt-$(BOARD)-vmlinux.lzma \
- -r $(BIN_DIR)/openwrt-$(BOARD)-root.$(1) \
- -o $(BIN_DIR)/openwrt-$(BOARD)-ubnt2-$(1).bin
-endef
-
-$(eval $(call BuildImage))
-
-\end{Verbatim}
-
-\begin{itemize}
- \item \texttt{Image/BuildKernel} \\
- This template defines changes to be made to the ELF kernel file
- \item \texttt{Image/Build} \\
- This template defines the final changes to apply to the rootfs and kernel, either combined or separated
- firmware creation tools can be called here as well.
-\end{itemize}
projects / openwrt / staging / yousong.git / blobdiff