C³APSULe: Cross-FPGA Covert-Channel Attacks through Power Supply Unit Leakage

Abstract

Field-Programmable Gate Arrays (FPGAs) are versatile, reconfigurable integrated circuits that can be used as hardware accelerators to process highly-sensitive data. Leaking this data and associated cryptographic keys, however, can undermine a system's security. To prevent potentially unintentional interactions that could break separation of privilege between different data center tenants, FPGAs in cloud environments are currently dedicated on a per-user basis. Nevertheless, while the FPGAs themselves are not shared among different users, other parts of the data center infrastructure are. This paper specifically shows for the first time that powering FPGAs, CPUs, and GPUs through the same power supply unit (PSU) can be exploited in FPGA-to-FPGA, CPU-to-FPGA, and GPU-to-FPGA covert channels between independent boards. These covert channels can operate remotely, without the need for physical access to, or modifications of, the boards. To demonstrate the attacks, this paper uses a novel combination of "sensing" and "stressing" ring oscillators as receivers on the sink FPGA. Further, ring oscillators are used as transmitters on the source FPGA. The transmitting and receiving circuits are used to determine the presence of the leakage on off-the-shelf Xilinx boards containing Artix 7 and Kintex 7 FPGA chips. Experiments are conducted with PSUs by two vendors, as well as CPUs and GPUs of different generations. Moreover, different sizes and types of ring oscillators are also tested. In addition, this work discusses potential countermeasures to mitigate the impact of the cross-board leakage. The results of this paper highlight the dangers of shared power supply units in local and cloud FPGAs, and therefore a fundamental need to rethink FPGA security for shared infrastructures.

Maya: Using Formal Control to Obfuscate Power Side Channels

“…Cloud systems share FPGAs across processors and accelerators, and can be exploited for remote power measurement. 4 In multicore systems, the hierarchical power management policies can be abused to act as power covert channels between cores.…”

“…These attacks can steal information like the identity of the running applications, keystrokes typed, and browser data accessed. This threat model covers the majority of attacks described earlier (e.g., the work of Lifshits et al, 1 Shao et al, 3 Giechaskiel et al, 4 and Masti et al 6 ), except for those attacks identifying encryption keys. 7 The latter attacks are harder to mount, and typically need more detailed knowledge of the cryptosystem being attacked.…”

“…They can also use hardware methods, such as direct probing, antennas, indirect measurement by tapping electrical outlets and power supply networks, trojan chips, field-programmable gate arrays (FPGAs), and circuits. 3,4 Since most of these techniques simply collect measurements, they cause little interference in the target computer and are hard to detect.…”

Power to Pulse Width Modulation Sensor for Remote Power Analysis Attacks

“…In a typical RPA attack, the attacker has to rely on covert communication channels for communicating with the on-chip sensor. Covert communication channels in general can only support lower bandwidths [GRS20] and therefore, it is crucial for the attacker to devise an on-chip sensor that demands minimum communication bandwidth.…”

Modeling and Analysis of Switched-Capacitor Converters as a Multi-port Network for Covert Communication

“…A covert communication can also be established via the power management units, which control voltage level and operating frequency. A covert channel attack among FPGAs, CPUs, and GPUs that are connected to the same power supply unit is proposed in [10]. By modulating the core frequency with dynamic frequency scaling (DFS) technique, a covert channel has been created in a multi-core platform [11].…”