4 ms·

Somewhat related: I was in China recently, and bought a SIM at the airport. You know those arrows on the mobile data icon in the notification bar on Android tha

Somewhat related: I was in China recently, and bought a SIM at the airport. You know those arrows on the mobile data icon in the notification bar on Android that tell you whether your device is actively transferring data? The upload arrow was on non-stop, the entire time I was there. I still have no clue what it was doing.

Gorbzel 8y ago
Pretty obvious, it was uploading your personal data to the state.
- bspammer 8y ago
  That's basically what I assumed, but I wasn't aware that SIM cards had that kind of access to the device storage. I thought at minimum it was sending out my location constantly though. I know next to nothing about telecoms technology, but in my head always assumed that SIMs were basically just read-only chips containing keys to authorise the phone to use the network. Clearly my assumption was wrong in some way.
  - allispwned 8y ago
    SIM cards can contain applets that execute on the baseband. The baseband often uses the same system memory as the application cpu (where android runs), and might even be in the same package or on the same silicon. In theory devices shipped with an MMU to prevent the baseband from fucking with the application processor. In reality, even Qualcomm ships broken MMU configs, and don't bother to ship a fix until the device is near EOL. I can't even imagine the horror show of Mediatek's MMU. Of course it's also possible that this is Google playing nice with Chinese legislation...
  - jobigoud 8y ago
    SIM cards are actually small computers that can run Java. http://simhacks.github.io/defcon-21/ http://simhacks.github.io/defcon-21/
Rjevski 8y ago
The most likely explanation is that you had applications that were trying to connect to censored servers, so it was just always retrying, but never getting any data back (so the download arrow wouldn’t show).
- bspammer 8y ago
  Interesting, I hadn't considered that.

Gorbzel 8y ago

Pretty obvious, it was uploading your personal data to the state.

bspammer 8y ago
That's basically what I assumed, but I wasn't aware that SIM cards had that kind of access to the device storage. I thought at minimum it was sending out my location constantly though. I know next to nothing about telecoms technology, but in my head always assumed that SIMs were basically just read-only chips containing keys to authorise the phone to use the network. Clearly my assumption was wrong in some way.
- allispwned 8y ago
  SIM cards can contain applets that execute on the baseband. The baseband often uses the same system memory as the application cpu (where android runs), and might even be in the same package or on the same silicon. In theory devices shipped with an MMU to prevent the baseband from fucking with the application processor. In reality, even Qualcomm ships broken MMU configs, and don't bother to ship a fix until the device is near EOL. I can't even imagine the horror show of Mediatek's MMU. Of course it's also possible that this is Google playing nice with Chinese legislation...
- jobigoud 8y ago
  SIM cards are actually small computers that can run Java. http://simhacks.github.io/defcon-21/ http://simhacks.github.io/defcon-21/

Rjevski 8y ago

The most likely explanation is that you had applications that were trying to connect to censored servers, so it was just always retrying, but never getting any data back (so the download arrow wouldn’t show).

bspammer 8y ago
Interesting, I hadn't considered that.