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GTI9100GBootloaderFreedom » History » Version 26

Denis 'GNUtoo' Carikli, 03/25/2020 04:57 AM

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h1. I9100GBootloader
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h2. Findings, TODO and status
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* The I9100G of hpagseddy is unsigned but the omap-usb-tool says the soc is in HS mode.
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* If I recall well, the string was verified by hpagseddy, so MLO was flashed and ran
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* MLO was flashed through heimdall frmo Android 4.x bootloader's odin mode
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* GNUtoo laptop works fine with heimdall with Android 2.3.6 bootloader while GNUtoo desktop doesn't
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** The device can easily be stuck in "PC screen mode" with the Android 2.3.6 bootloader, so beware if your computer doesn't manage to talk to heimdall in that mode
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** It might be related to USB timings or to the unfinished coreboot port for the F2A85M-PRO or the fact that I don't use nonfree firmware/fpga binary for the USB3 on the F2A85M-PRO so the machine is stuck on USB2 with USB3 hardware and I've no idea if that has some impacts or not. My laptop is a Thinkpad X200 with USB2.
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We need to solve this OMAP HS mystery:
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* I've looked at u-boot, barebox, linux, crucible and I didn't find any driver or code for fuses for any OMAP SOC.
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* GNUtoo is in Paris where we're confined in our homes due to COVID-19 and I can't afford to brick my GT-I9100G
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* It might be due to the fuses having been programmed with the hash of a key / certificate but not being in enforcing mode.
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* The website for breaking motorolla restricted boot is only about OMAP3 devices but it contains infos on the structure of signed MLO
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* I've tried loading hpagseddy's MLO from USB with omap-usb-tool and I cound't validate that the code ran:
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** I tried playing with the WDT (easy) => no difference
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** I tried printing something to the UART in a for(;;) loop => no difference
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* I've extracted the MLO but I'm unsure of its size and when I sent it through USB to the bootrom it failed. It might be because of the sram size limit but anyway as I don't know how to parse signatures yet (I need to look at the wiki for breaking motorolla restricted boot) I'm unsure of the exact binary size to send. Once I can parse that stuff, I will know the exact size of the signed area and so of the binary.
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* I've not managed to get any difference by booting from mmc1
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* I've not dumped yet the usual register for booting configuration like SYS_BOOT
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TODO while reading the TRM:
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* check the device's OMAP4 the sram size limit
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* check the load address / memory mapping of MLO in case of USB boot or boot from eMMC.
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* Check mmc1 booting constraint (card size, look if < 4GiB works)
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* Read about SYS_BOOT and booting, though fuse infos is most probably missing
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If infos about fuses are ever found:
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* Ideally write drivers and upstream them in Linux, u-boot, Barebox and crucible
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h2. How to check if you have a signed bootloader
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h3. How to check from the bootloader interface to install the recovery.
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To do that you need to get into the ODIN MODE that is typically used to install the Replicant recovery:
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# Start the device by holding the following key combination: *Volume down, Select, Power*,
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# Hold the key combination until the device shows a *Warning* message.
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# Confirm that you want to download a custom OS using volume up
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# Make sure the device is in *Downloading* mode
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When this is done, it should show some text:
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<pre>
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ODIN MODE
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PRODUCT NAME: GT-I9100G_CHN_CHN
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</pre>
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Here CHN_CHN probably refers to the Chinese version. And it looks like that version has a signed bootloader: According to "a thread on the XDA developers forum":https://forum.xda-developers.com/galaxy-s2/development/guide-repair-totally-sleep-dead-boot-t1701471 "Means that you own a chinese bootloader locked I9100G. You can't flash any other bootloader than the chinese one."
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h3. How to check with command line utilities
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To get the bootrom to try to boot on USB, you need to do the following:
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* Connect the USB cable to the device but make sure it's not connected on the computer.
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* Power off the device
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* Connect the USB cable
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If we do that, we get the following in the kernel log of your laptop:
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<pre>
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usb 1-1: new high-speed USB device number 24 using ehci-pci
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usb 1-1: unable to get BOS descriptor or descriptor too short
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usb 1-1: New USB device found, idVendor=0451, idProduct=d00f, bcdDevice= 0.00
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usb 1-1: New USB device strings: Mfr=33, Product=37, SerialNumber=0
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usb 1-1: Product: OMAP4430
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usb 1-1: Manufacturer: Texas Instruments
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</pre>
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Note that your kernel might need to be compiled with CONFIG_USB_ANNOUNCE_NEW_DEVICES=y
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to print that. In Parabola CONFIG_USB_ANNOUNCE_NEW_DEVICES=y is enabled.
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We can also try to get a bit more infos with omap-usb-boot:
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<pre>
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$ sudo omap-usb-boot -v -w boot invalidbootmedia
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Finding and opening USB device
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Found and opened omap4 USB device: OMAP4430
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ASIC device id: 4430, HS device
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Booting from device invalidbootmedia...
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Booting device invalidbootmedia not found
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Booting from device failed
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</pre>
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Here we know the device is signed because it's a "HS device".
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If it was not signed it would print "GP device" instead.
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h3. Using the Android version or other devices properties?
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"hpagseddy/i9100g_xloader":https://github.com/hpagseddy/i9100g_xloader is based on "ths-backup/i9100g_xloader":https://github.com/ths-backup/i9100g_xloader which has an ics (Icecream Sandwitch, an Android version) branch only. According to hpagseddy, that branch is also used for Android Jelly brean.
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It's still unclear if there is some correlation between Android version and signed bootloaders.
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The device that was given to [[People#Denis-GNUtoo-Carikli|GNUtoo]] that has a signed bootloader also has the following characteristics:
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*Software state*: Running the stock OS, unmodified
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*Android version*: Android 2.3.6
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*Baseband version*: IG9100GZCLC2
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*Build number*: GINGERBREAD.ZCLC2
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*Kernel version*: 2.6.35.7 se.infra@SEI-30#2
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According to "a thread on XDA":https://forum.xda-developers.com/galaxy-s2/development/bootloader-t1754158 there is a corelation between the @Baseband version@ and the geographic zone that is targeted. And as we can see above, the @Build number@ seem to be related to the @Baseband version@ as well. While the list of baseband versions is incomplete, we can still use it to avoid the Chinese version (CHN_CHN) which has a signed bootloader. 
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At this point it's also still unclear if any of the other characteristics above correlate to signed or unsigned bootloaders.
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As the binaries are under the GPLv2 or later, It would also be a good idea to collect all of them, match them with the device characteristics like the @Build@ number and @Baseband version@, and verify if they are signed or not with some free software tool.
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We could even publish the unsigned versions. As for the signed versions, if they cannot run on devices that don't enforce bootloader signatures, it would probably not be a good idea to publish them as the binaries wouldn't respect the 4 freedoms, but we can still check with the FSF if they have good ideas on that point.
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h2. Source code
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* https://github.com/hpagseddy/i9100g_xloader This got rebuilt and flashed, and it worked on the device it was tested on.
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* https://blog.the-leviathan.ch/?p=408
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h2. TODO
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* Document the various firmware version mentioned here: https://www.sammobile.com/samsung/galaxy-s2/firmware/#GT-I9100G
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* Understand how to get unsigned versions (Android version, serial number, etc)
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* Get a device with an unsigned bootloader and u-boot and ask samsung for source code
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* Check the boot order on unsigned devices (is it possible to boot from USB easily?)
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* Try to boot the xloader nevertheless, as the device could be in some "verify but not enforce mode" for signatures