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The availability of FPGAs in cloud data centers offers rapid, on-demand access to reconfigurable hardware compute resources that users can adapt to their own needs. However, the low-level access to the FPGA hardware and associated resources such as the PCIe bus, SSD drives, or DRAM modules also opens up threats of malicious attackers uploading designs that are able to infer information about other users or about the cloud infrastructure itself. In particular, this work presents a new, fast PCIe-contention-based channel that is able to transmit data between FPGA-accelerated virtual machines by modulating the PCIe bus usage. This channel further works with different operating systems, and achieves bandwidths reaching 20 kbps with 99% accuracy. This is the first cross-FPGA covert channel demonstrated on commercial clouds, and has a bandwidth which is over 2000 × larger than prior voltage- or temperature-based cross-board attacks. This paper further demonstrates that the PCIe receivers are able to not just receive covert transmissions, but can also perform fine-grained monitoring of the PCIe bus, including detecting when co-located VMs are initialized, even prior to their associated FPGAs being used. Moreover, the proposed mechanism can be used to infer the activities of other users, or even slow down the programming of the co-located FPGAs as well as other data transfers between the host and the FPGA. Beyond leaking information across different virtual machines, the ability to monitor the PCIe bandwidth over hours or days can be used to estimate the data center utilization and map the behavior of the other users. The paper also introduces further novel threats in FPGA-accelerated instances, including contention due to network traffic, contention due to shared NVMe SSDs, as well as thermal monitoring to identify FPGA co-location using the DRAM modules attached to the FPGA boards. This is the first work to demonstrate that it is possible to break the separation of privilege in FPGA-accelerated cloud environments, and highlights that defenses for public clouds using FPGAs need to consider PCIe, SSD, and DRAM resources as part of the attack surface that should be protected.
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Temporal Thermal Covert Channels in Cloud FPGAs
With increasing interest in Cloud FPGAs, such as Amazon's EC2 F1 instances or Microsoft's Azure with Catapult servers, FPGAs in cloud computing infrastructures can become targets for information leakages via convert channel communication. Cloud FPGAs leverage temporal sharing of the FPGA resources between users. This paper shows that heat generated by one user can be observed by another user who later uses the same FPGA. The covert data transfer can be achieved through simple on-off keying (OOK) and use of multiple FPGA boards in parallel significantly improves data throughput. The new temporal thermal covert channel is demonstrated on Microsoft's Catapult servers with FPGAs running remotely in the Texas Advanced Computing Center (TACC). A number of defenses against the new temporal thermal covert channel are presented at the end of the paper.
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- Award ID(s):
- 1651945
- PAR ID:
- 10089256
- Date Published:
- Journal Name:
- International Symposium on Field-Programmable Gate Arrays (FPGA)
- Page Range / eLocation ID:
- 298 to 303
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3289602.3293920
