Evaluating Vulnerability of Chiplet-Based Systems to Contactless Probing Techniques

TL;DR

This paper investigates the security vulnerabilities of chiplet-based systems, demonstrating that contactless laser probing can effectively access interposer wires and that existing delay-based sensors are ineffective against such attacks.

Contribution

It provides the first evaluation of laser contactless probing on chiplet-based FPGA systems, highlighting specific vulnerabilities and limitations of current protective measures.

Findings

Probing interposer wire drivers is easier than internal nodes.

Laser probing causes a delay change of only 0.792ps at full power.

Delay-based sensors are ineffective against laser contactless probing.

Abstract

Driven by a need for ever increasing chip performance and inclusion of innovative features, a growing number of semiconductor companies are opting for all-inclusive System-on-Chip (SoC) architectures. Although Moore's Law has been able to keep up with the demand for more complex logic, manufacturing large dies still poses a challenge. Increasingly the solution adopted to minimize the impact of silicon defects on manufacturing yield has been to split a design into multiple smaller dies called chiplets which are then brought together on a silicon interposer. Advanced 2.5D and 3D packaging techniques that enable this kind of integration also promise increased power efficiency and opportunities for heterogeneous integration. However, despite their advantages, chiplets are not without issues. Apart from manufacturing challenges that come with new packaging techniques, disaggregating a design into multiple logically and physically separate dies introduces new threats, including the possibility of tampering with and probing exposed data lines. In this paper we evaluate the exposure of chiplets to probing by applying laser contactless probing techniques to a chiplet-based AMD/Xilinx VU9P FPGA. First, we identify and map interposer wire drivers and show that probing them is easier compared to probing internal nodes. Lastly, we demonstrate that delay-based sensors, which can be used to protect against physical probes, are insufficient to protect against laser probing as the delay change due to laser probing is only 0.792ps even at 100\% laser power.