First small steps toward free GSM firmware

Sebastian Krzyszkowiak dos at
Sat Nov 16 00:44:05 CET 2013

On Sat, Nov 16, 2013 at 12:33 AM, Neal H. Walfield <neal at> wrote:
> As long as the modem and CPU only communicate via the serial port,
> i.e., there is no shared memory, then the application CPU is
> (relatively) safe from attacks started from the baseband CPU.  As I
> understand it, this is the case for the GTA0*, but it would be good to
> have confirmation of this from someone better in the know.
> Neal

Yes. GTA01 and GTA02 communicate with modem (TI Calypso) via serial
port, and GTA04 (with Option GTM601W) via USB.

While so called "dumbphones" and some older "smartphones" like Symbian
devices often didn't have dedicated APU, so complete OS was
technically running on modem, newer devices have rather good
separation of those two processors. However, it's not always the case
- there are some devices that communicate with modem via shared RAM.
It starts to be pretty common on Android devices. It's still hardly
any news, it's perfectly known for few years, and projects like
Replicant were actively discouraging usage of such phones ever since.

Anyway, it's not a secret, one can easily check by some quick googling
if the device he/she's interested in follows this design.

It's good to raise awareness about problems with such design. It's bad
to make it sound like some secret conspiracy. Like we haven't got
enough of true secret conspiracies to worry about ;)

Sebastian Krzyszkowiak, dos

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