A buffer overflow attack is perhaps the most common attack used to compromise the security of a host. A buffer overflow can be used to change the function return address and redirect execution to execute the attacker's code. We present a hardware-based solution, called SmashGuard, to protecting the return addresses stored on the program stack. SmashGuard protects against all known forms of attack on the function return address pointer. With each function call instruction a new return address is pushed onto an extra hardware stack. A return instruction compares its return address to the address from the top of the hardware stack. If a mismatch is detected, then an exception is raised. Because the stack operations and checks are done in hardware, and in parallel with the usual execution of call and return instructions, our bestperforming implementation scheme has virtually no performance overhead. While previous software-based approaches' average performance degradation for the SPEC2000 benchmarks is only 2.8%, their worst-case degradation is up to 8.3%. Apart from the lack of robustness in performance, the software approaches' key disadvantages are less security coverage and the need for recompilation of applications. SmashGuard, on the other hand, is secure and does not require recompilation, though the OS needs to be modified to save/restore the hardware stack at context switches, and when function call nesting exceeds the hardware stack depth.
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