Laser Your Manner Into Debug Mode On The RP2350

The RP2350 is definitely a reasonably safe chip, all issues thought of. It has safe boot, ARMv8’s TrustZone to separate safe and non-secure execution, and you’ll completely disable debug — the Pi Foundation even included glitch detection, that means the standard ‘zap the chip till it obeys’ approach is blocked. That’s why the [Ledger Donjon] safety group went full Bond Villain and strapped everybody’s favorite fruit-flavoured microcontroller to a desk with a slowly-approaching laser beam.

Okay — film clichés apart, the laser was actually very rigorously targeted heading in the right direction earlier than they turned it on. That goal was the register that allows the 2350’s debug options. Said register was situated by decapsulating the chip and analyzing the die with photon-emission electron microscopy; the precise assault was carried out on a chip that had been decapped on the again aspect, with IR shining by the silicon wafer. There was most likely greater than a bit of trial-and-error to determine precisely the place on the die adjoining to the register to zap with the laser to flip these bits. But flip they did, restoring the debugger’s entry to the safe execution zone. Then, after resetting the chip, [Ledger]’s group learn the 128-bit secret the Pi Foundation hid in reminiscence as a part of the 2350 hacking challenge.

It’s lengthy been accepted that when the black hats — or white hats, for that matter — have their fingers in your {hardware}, they’re going to discover a method in. The effort it takes to interrupt right into a easy microcontroller right here is definitely form of spectacular. We’ve talked about laser fault injection earlier than; sarcastically, we’ve additionally featured Pi Pico-powered glitching attacks — the sort that this chip’s glitch detection thwarts.