Method and apparatus for ensuring control flow integrity

A computer-implemented system for enforcing control flow of a program, comprising:

• memory for storing a plurality of control flow rules generated for a portion of code, each control flow rule being associated with at least one possible attack mechanism for a security attack to the portion of code and based upon expected execution of the portion of code in accordance with a reference control flow, wherein the reference control flow is generated based on the portion of code during an execution of the portion of code under a normal operating condition, and wherein the reference control flow indicates the expected execution of the portion of code;
• at least one processor configured to execute the portion of code;
• a rule checking component arranged to evaluate a control flow rule during execution of the portion of code by a processor from the control flow rules based on a condition experienced during the execution of the portion of code to detect a deviation from the expected execution of the portion of code indicated in the reference control flow based on bus signals and internal signals from the processor, analyse the portion of code to derive the reference control flow and to identify the at least one possible attack mechanism for the security attack, test the control flow rules against the reference control flow and recording a number of attack mechanisms eliminated by each rule, and identify a subset of the control flow rules to provide a reduced rule set, wherein the reduced rule set eliminates a maximum number of attack mechanisms;
• and
• an intervention component arranged to generate a response upon detection of a deviation from the reference control flow wherein the response is based on the deviation and selected from a plurality of responses, and wherein the response is encoded as part of the control flow rule.