  Continued expansion of cloud computing offerings now includes SmartSSDs. A
SmartSSD is a solid-state disk (SSD) augmented with an FPGA. Through public
cloud providers, it is now possible to rent on-demand virtual machines enabled
with SmartSSDs. Because of the FPGA component of the SmartSSD, cloud users who
access the SmartSSD can instantiate custom circuits within the FPGA. This
includes possibly malicious circuits for measurement of power and temperature.
Normally, cloud users have no remote access to power and temperature data, but
with SmartSSDs they could abuse the FPGA component to learn this information.
This paper shows for the first time that heat generated by a cloud user
accessing the SSD component of the SmartSSD and the resulting temperature
increase, can be measured by a different cloud user accessing the FPGA
component of the same SmartSSD by using the ring oscillators circuits to
measure temperature. The thermal state remains elevated for a few minutes after
the SSD is heated up and can be measured from the FPGA side by a subsequent
user for up to a few minutes after the SSD heating is done. Further, in a
future multi-tenant SmartSSD setting, the thermal changes can be measured in
parallel if one user controls the SSD and the other the FPGA. Based on this
temporal thermal state of the SmartSSD, a novel thermal communication channel
is demonstrated for the first time.
