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Question: Permanently disabling GSM modem in Galaxy S3/I9300?

Added by NS von H almost 2 years ago

Hi, I'm going to only use wifi for connectivity so I would like to completely disable GSM modem in my phone.

The wiki page on I9300 (http://redmine.replicant.us/projects/replicant/wiki/GalaxyS3I9300PrivacySecurityEvaluation) says that the system has to "ask" the modem to switch off so I cannot be sure that it's really off. So my idea is to at least making the modem inoperable so it cannot connect to the network even if being powered on all the time.

Paul Kocialkowski said in his post http://code.paulk.fr/article16/missing-proprietary-firmwares-in-android-systems#c1429611192-1:
"The modem firmware (...) is preinstalled on the device and loaded to the modem by Replicant at boot time."

So my questions are:
1) Where is this firmware file(s) stored?
2) How can I prevent the firmware from being loaded onto the modem?
3) Is the modem inoperable without the firmware? In other words can it connect to the network?

Currently, after a fresh Replicant installation I can see in "Settings -> About phone -> Status" that the modem has connected to one of the GSM operators (even though the SIM card has not been inserted). This means that by default Replicant loads modem firmware and this is precisely what I would like to avoid.

Thanks


Replies (13)

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Wolfgang Wiedmeyer almost 2 years ago

1) The firmware is stored on the internal storage of the device, on a separate partition. Replicant and your data are on different partitions.

2) The firmware is loaded by the radio interface at boot. So you could try to disable the radio interface. I didn't test the following steps, but they should work:
  1. enable adb and root over adb in the developer settings
  2. connect the device to your PC and run
    adb root
    adb remount
    adb shell mv /system/lib/libsamsung-ril.so /system/lib/libsamsung-ril.so.disabled
    

    Then reboot.
    If you want to restore the interface, you would need to run the commands again while moving the ril back to its old place.

3) It should be inoperable, at least that's what I learned from Paul.

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by NS von H almost 2 years ago

Thanks for your help Wolfgang and Paul.

I was able to rename the file in the file manager with root access.
It looks like the modem is not working now and it is not connected to the network.

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Ellen Ripley over 1 year ago

Hi.

That seems a really important security feature, thank you Wolfgang and NS von H. As far as I understand that would let us enjoy the freedom of not being tracked -please let me know if I am correct.

It would be very nice if someone could write a graph app for that. Just a button to turn the modem on and off, without having to connect to a computer to run those adb commands.

Actually, I think Replicant should not boot with the modem on by default. I think it should boot with the modem off by default.

Maybe that graphical app could have a button to turn the modem on and off on the fly, and also the following options:

a) When booting, keep modem off and ask the user if she wants to have it on (default)
b) When booting, keep modem off
c) When booting, turn modem on

I guess I should open an issue for it...

Cheers

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Wolfgang Wiedmeyer over 1 year ago

There is already an issue for this: #1779. AFAIK nobody is working on this right now and I won't have time for this as I'm already busy with other tasks. So code contributions are greatly appreciated!

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Finn Ryan over 1 year ago

Would this actually stop the modem from pinging towers and hence tracking you? Maybe you can open the phone up and disconnect the antenna. Although I think, at least on the S2, the antenna is on the same little board as USB, both using the antenna cable to connect to mainboard.

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Wolfgang Wiedmeyer over 1 year ago

Yes, it should make the modem inoperable and thus, there should be no mobile network activity whatsoever from the phone. I don't know what could be done regarding the antenna.

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Thomas Heid over 1 year ago

Would it be possible to wipe completely the partition holding the modem firmware to assure that there is no network activity? This has been done on a 2013 Google Nexus 7 tablet (https://blog.torproject.org/blog/mission-impossible-hardening-android-security-and-privacy), but I know some Samsung smartphones go into a bootloop without the firmware.

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Kurtis Hanna over 1 year ago

Some traction seems to have been made on the issue tracker for this: https://redmine.replicant.us/issues/1779

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by gufo gufo 2 months ago

I am thinking of getting a Replicant supported device, maybe S3 or Note2. However I don't want (or need) the modem to be able to communicate with the towers. Is there a hardware solution? I was thinking of removing the antenna and running in airplane mode (to prevent battery drain). Is this feasible? What would I need to remove and would it completely block the modem? Will it affect anything else?

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Fil Bergamo 2 months ago

gufo gufo wrote:

I am thinking of getting a Replicant supported device, maybe S3 or Note2. However I don't want (or need) the modem to be able to communicate with the towers.

Then I suggest you turn towards a Galaxy Note 8 Tablet, n5110
It's not actually a phone, and it's quite bigger than the ones you mentioned, but model n5110 comes without a GSM modem, so you wouldn't have to worry about disabling it..

Other wifi-only tablets supported by Replicant are:
GalaxyTab270P31xx
GalaxyTab2101P51xx

Caution: each of them come in two different versions: one with GSM and one without.
Please, refer to the links above to tell the differences.

I personally suggest the N5110. I own one and it's flashy-fast compared to other Replicant-supported devices.
Also, the battery is powerful enough to drive an external wifi dongle without any pain, so wifi is much more stable than in other devices.

Is there a hardware solution?

None that I'm aware of.

I was thinking of removing the antenna and running in airplane mode (to prevent battery drain). Is this feasible? What would I need to remove and would it completely block the modem?

I don't know about removing the antenna, but for sure "aeroplane mode" does not guarantee the modem to be completely disabled, as it's only a software setting that "kindly asks the modem to turn off". Still the operating system has no way to force the modem to stop contacting towers.

Will it affect anything else?

Aeroplane mode could potentially interfere with the correct functioning of RepWifi (maybe it does not interfere but I can't guarantee). But, after all, it is a setting that is easily reverted, so you can always turn it back again when you need to use wifi.

Lastly, there are some shell scripts by Jeremy Rand that work form some of the supported phones.
The actual effectiveness of the scripts on radio emissions is not tested and therefore is not guaranteed.
A research was planned, that involved the potential use of a femto-tower, to actually test for any residual radio emission after excluding the modem. Unfortunately we never had a chance to perform such a test..
Please, have a look at feature request #1779 for more details.

Please ask back if you need any clarifications.

Happy hacking,

Fil

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by gufo gufo 2 months ago

Tablets aren't an option since I need something that I can carry in my pocket.

Is there some reason N5110 doesn't appear in the list of supported devices?

Regarding airplane mode, notice the "and". Airplane mode would be just to prevent any battery drain due to modem continuously trying to find towers. Antenna removal or something else would block communication.

#1779 was pointed out earlier and I did have a look at it. It is about "toggling" the RIL service, isn't it? Isn't the modem still running? RIL is just for communication between the Android OS and the modem, isn't it? Can't the network track you or do other shady things?

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by gufo gufo 2 months ago

N5110 is in the list in the wiki but not on the main site. (https://replicant.us/supported-devices.php)

Maybe someone should fix that page since its a newer version than the other two tablets.

RE: Question: Permanently disabling GSM modem in Galaxy S3/I9300? - Added by Fil Bergamo 2 months ago

gufo gufo wrote:

N5110 is in the list in the wiki but not on the main site. (https://replicant.us/supported-devices.php)

Thanks for pointing out.
I'm preparing a patch for that as soon as possible.
Progress is tracked on #1898.

Cheers

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