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Self-Healing Control Flow Protection in Sensor Applications

This article explores innovative self-healing methodologies tailored for sensor applications, focusing on maintaining control flow and data protection despite resource constraints. Due to the simplicity of operating systems and application software in these devices, effective error recovery systems are often lacking. We propose a strategy involving the division of programs into blocks with unique labels, enabling the detection of illegal transitions. This approach involves sophisticated randomness injections during compilation to protect label integrity and improve recovery processes.

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Self-Healing Control Flow Protection in Sensor Applications

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  1. Self-Healing Control Flow Protection in Sensor Applications

  2. Motivation • Sensors usually have very tight resources and use very simple OS and application software • Data/System memory are not separated • System/User tasks are not isolated • No recovery scheme: crash and reboot • Cannot embed complicated protection methods into the system • Still need to protect the memory/OS image

  3. Approach from 500 miles away • Divide the program into blocks and generate control flow graph • Assign a different label to each program block. When transitions among blocks happen, examine the labels to make sure such transitions are legal • If not, remove the task and take back the resources to clean it up

  4. Overview of the program structure

  5. Details of the design • Divide programs into blocks • Every function is a Control Node • Can detect only illegal transitions among functions

  6. How to detect illegal transitions • Each CN is assigned with a label value • When we enter the function, Rx = label • When we leave the function, we check again whether or not the label ?= Rx • If attackers have control the program and jump into another function, the label will have a different value

  7. New problem: how to protect the label value • At the compilation time, inject randomness so that every sensor has different access control code segments • The labels are in write-protected program memory • What is the label anyway: • A 8-bit or 16-bit random number

  8. How to recovery • Sensor OS can handle only one task at a time • Therefore, just kill that task and get back all the resources will be fine • Not as simple as this when we consider the memory management scheme

  9. Now we have separated kernel memory and task memory • During recovery • Release the task related memory • Release the I/O resources • Remove the current task from the task queue • Fetch the next task

  10. Discussion • Where do we put the label • Rx can be in registers or memory space • But where do we put the label of each function?

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