h1. GT-I9100G Bootloader Freedom

{{toc}}

h2. Findings, TODO and status

See [[OMAPBootrom]] for more information on the OMAP restricted boot.

* 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.
* I've not managed to get any difference by booting from mmc1
* I've not dumped yet the usual register for booting configuration like SYS_BOOT

Last news 27/03/2919:
hpagseddy and GNUtoo tried several tests on their respective devices, and the device always ended up going to the battery charging screen:
* Building xloader and loaing it with omap-usb-boot through USB
* Same with the addition of a for(;;) loop in the code to see if it hangs (it's supposed to if the code runs)
* Same but with the watchdog being configured to reboot after 1 second (it's supposed to reboot if the code is correct and runs)

hpagseddy and GNUtoo also found that when using odin to flash the MLO partition, odin interface makes the user think that the MLO partition was flashed correctly, while odin didn't flash anything. That may be due to the partition being set Read-Only and/or to the "File Offset" and "File Size" being 0.
<pre>
-- Entry #0 ---
Binary Type: 0 (AP)
Device Type: 2 (MMC)
Identifier: 1
Attributes: 0 (Read-Only)
Update Attributes: 0
Partition Block Size/Offset: 0
Partition Block Count: 0
File Offset (Obsolete): 0
File Size (Obsolete): 0
Partition Name: X-loader
Flash Filename: MLO
FOTA Filename: 
</pre>

We know that nothing was successfuly flashed as we dumped MLO, and verified that the binary was signed by looking if it contained the strings that indicate that (PRIMAPP, KEYS, CertPK_)

h2. MLO versions

As MLO is under the GPLv2+, its binaries are also under that license.

This means that if the binaries are not signed, they are legally speaking and practically speaking free software. So if we find the full and corresponding source code (which is or was probably distributed by Samsung on opensource.samsung.com) we can use them and redistribute them very easily.

As for the signed versions, while we can legally distribute them as well, as they are legally under a free software license, they are signed with keys that users don't have. If users don't have the ability to run modified version then they are practically speaking not free software.

Weather or not the binaries also work on unsigned devices and if they can be modified on such devices remains to be tested.

|_. Device |_. Android version |_. String | Signed | Reference | Updates history |
| ? | ? | Texas Instruments X-Loader 1.41 (Jan 11 2012 - 23:25:41) | ? | "leviathan's blog":https://blog.the-leviathan.ch/?p=408 |
| I9100G_CHN_CHN | Android 2.3.6 | Texas Instruments X-Loader 1.41 (Mar 20 2012 - 11:20:26) | Yes | GNUtoo's device | * It came with the signed unmodified stock OS
* A custom recovery for 2.3.6 found on XDA was installed
* The bootloader wasn't touched
* Beside KERNEL, and RECOVERY, the rest of the partitions were left untouched |
| I9100G_CHN_CHN | Android 4.1.2 | Texas Instruments X-Loader 1.41 (Jun 27 2013 - 18:34:17) | Yes | hpagseddy's device | * It came with Android 4.0.4
* It was upgraded to 4.1.2 and many community custom distributions were installed |

h2. How to check if you have a signed bootloader

h3. How to check from the bootloader interface to install the recovery.

To do that you need to get into the ODIN MODE that is typically used to install the Replicant recovery:

# Start the device by holding the following key combination: *Volume down, Select, Power*,
# Hold the key combination until the device shows a *Warning* message.
# Confirm that you want to download a custom OS using volume up
# Make sure the device is in *Downloading* mode

When this is done, it should show some text:
<pre>
ODIN MODE
PRODUCT NAME: GT-I9100G_CHN_CHN
</pre>

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."

h3. How to check with command line utilities

See [[FindOMAPDevicesWithUnsignedBootloderFromUSB]] for how to do that.

h3. Using the Android version or other devices properties?

"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.

It's still unclear if there is some correlation between Android version and signed bootloaders.

The device that was given to [[People#Denis-GNUtoo-Carikli|GNUtoo]] that has a signed bootloader also has the following characteristics:

*Software state*: Running the stock OS, unmodified
*Android version*: Android 2.3.6
*Baseband version*: IG9100GZCLC2
*Build number*: GINGERBREAD.ZCLC2
*Kernel version*: 2.6.35.7 se.infra@SEI-30#2

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. 

At this point it's also still unclear if any of the other characteristics above correlate to signed or unsigned bootloaders.

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.

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.

h2. Online resources

* "[GUIDE]Switch between Chinese I9100G & international I9100G SafeWay":https://forum.xda-developers.com/galaxy-s2/development/guide-switch-chinese-i9100g-t1916623 : Nothing conclusive. That guide applies only to the CHN_CHN version. Here people are booting signed MLO from USB to switch the second stage bootloader from the chinese version to the international version. That doesn't tell if other version of the device have signed or unsigned MLO.
* "[GUIDE][GT-I9100G]Repair Totally Sleep/Dead Boot Mode Via USB":https://forum.xda-developers.com/galaxy-s2/development/guide-repair-totally-sleep-dead-boot-t1701471 : It's not clear if it brings any information. Here we know that on the chinese versions "You can't flash any other bootloader than the chinese one." but it's not clear why. There is also logs from a tool, which is proprietary, that is meant to load code from USB but it's not super clear where the information it prints comes from (the files? the interaction with the SOC?). TODO: re-read the logs output from this tool and try to understand what's going on.
* Leviathan's blog with "I9100G, boot loader and UART":https://blog.the-leviathan.ch/?p=408 and "USB on Samsung Galaxy S2 (I9100G)":https://blog.the-leviathan.ch/?p=405 : After searching with a search engine in the blog, theses were the only 2 posts about the bootloader. There is no indication that an unsigned version of MLO was built and flashed to that device.
* http://forum.gsmhosting.com/vbb/f777/guide-samsung-gt-i9100g-usb-boot-repair-1488048/index3.html TODO: look into it

h2. TODO

* Document the various firmware version mentioned here: https://www.sammobile.com/samsung/galaxy-s2/firmware/#GT-I9100G
* Understand how to get unsigned versions (Android version, serial number, etc)
* Get a device with an unsigned bootloader and u-boot and ask samsung for source code
* Check the boot order on unsigned devices (is it possible to boot from USB easily?)
* Try to boot the xloader nevertheless, as the device could be in some "verify but not enforce mode" for signatures