Secure system firmware using interrupt generation on attempts to modify shadow RAM attributes

A method for use with a computer system having a central processing unit (CPU), a dynamic random access memory (DRAM) coupled to the CPU that comprises a shadow random access memory (RAM) including one or more registers whose attributes are separately configurable, and system firmware that runs on the CPU, the method comprising the steps of:

• initializing the DRAM and the shadow RAM;
• copying itself into the shadow RAM;
• setting LOCK bits associated with the registers of the shadow RAM;
• booting a computer operating system;
• monitors attempted writes to locked registers of the shadow RAM;
• and
• if a write operation to a locked register is detected, generating an interrupt that indicates an attempt to tamper with the system firmware.

Software for use with a computer system having a central processing unit (CPU), a dynamic random access memory (DRAM) coupled to the CPU that comprises a shadow random access memory (RAM) including one or more registers whose attributes are separately configurable, and system firmware that runs on the CPU, that comprises:

• a code segment that initializes the DRAM and the shadow RAM;
• a code segment that copies itself into the shadow RAM;
• a code segment that sets LOCK bits associated with the registers of the shadow RAM;
• a code segment that boots a computer operating system;
• a code segment that monitors attempted writes to locked registers of the shadow RAM;
• and
• a code segment that, if a write operation to a locked register is detected, generates an interrupt that indicates an attempt to tamper with the system firmware.