GTA04 Block V4

[Ian Stirling]

Werner Almesberger wrote:
> Ian Stirling wrote:
>> I think you can always mass-erase the chip though, so a USB bootloader  
>> would not survive malicious users.
> 
> It's even easier: according to the manual, you can simply turn off
> the protection and then scribble over things, see [1].
> 
>> As I read it, some of the STM32 family tick most of these.
> 
> Yes, they look very very good. Their main problem is that they seem
> brickable. This could be solved by booting from a serial flash
> (STR750 family, [2]), but that would add yet another component,
> which isn't desirable.
> 
If I read it correctly - you can secure the code - p22 of
http://www.st.com/stonline/products/literature/pm/13259.pdf says you 
can't overwrite pages 0-3 in read-protected mode, without mass-erasing.

This means you can't expose the serial bootloader directly to the user, 
or JTAG or SWD. But why would you?

Unless you're trying to secure the phone from users with debug boards, a 
fixed bootloader, which can talk over whatever interfaces you like, and 
handle updating in case of oopses, with new code loaded in only if
properly signed. (there is a USB bootloader example)

Users with debug boards get JTAG - but they should simply not brick it :)

And to answer the 'what if OM won't sign our stuff' - you can wipe out 
this code with the debug board.

> [1] "STR7 family Flash programming"
>     http://www.st.com/stonline/books/pdf/docs/11130.pdf
>     section 3.3.
> 
> [2] "STR750 ARM7TDMI-S-based microcontroller family Reference Manual"
>     http://www.ftp2u.com/datasheet/str75xf_m.pdf
>     sections 1.4 and 1.4.2.
> 
> Oh, and I forgot the most important requirement: fully documented
> without silly restrictions :)
> 
> - Werner
> 
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