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Self-Healing Control Flow Protection in Sensor Applications

Self-Healing Control Flow Protection in Sensor Applications. 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

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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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