Write protection of subroutine return addresses

A system for write protection of subroutine return addresses, the system comprising:

• means for calling a subroutine, including storing in a stack memory address a subroutine return address;
• means for locking, by a computer processor, the stack memory address against write access, including storing the stack memory address in a protected memory lockword, wherein the protected memory lockword comprises a portion of a protected content addressable memory;
• means for receiving in the computer processor an instruction to write data to the locked stack memory address, further comprising:
• means for receiving an instruction to write data to a memory address;
• and
• means for determining, in dependence upon protected memory lockwords, that the instruction to write data to a memory address is an instruction to write data to the locked stack memory, including means for placing the memory address on the input lines of the content addressable memory and means for identifying that the content addressable memory output line is set to ‘true’;
• and
• means for suspending execution of a current instruction stream in response to the instruction to write data to the locked stack memory address.

A computer program product for write protection of subroutine return addresses, the computer program product comprising:

• a recording medium;
• means, recorded on the recording medium, for calling a subroutine, including storing in a stack memory address a subroutine return address;
• means, recorded on the recording medium, for locking, by a computer processor, the stack memory address against write access, including storing the stack memory address in a protected memory lockword, wherein the protected memory lockword comprises a portion of a protected content addressable memory;
• means, recorded on the recording medium, for receiving in the computer processor an instruction to write data to the locked stack memory address, further comprising:
• means, recorded on the recording medium, for receiving an instruction to write data to a memory address;
• and
• means, recorded on the recording medium, for determining, in dependence upon protected memory lockwords, that the instruction to write data to a memory address is an instruction to write data to the locked stack
• memory, including means, recorded on the recording medium, for placing the memory address on the input lines of the content addressable memory and means, recorded on the recording medium, for identifying that the content addressable memory output line is set to ‘true’;
• and
• means, recorded on the recording medium, for suspending execution of a current instruction stream in response to the instruction to write data to the locked stack memory address.