A call port is a processor function on Intel ™ central processing units ( CPU ) . It allows dynamic change of CPU privilege level when using certain instructions. This allows lower-privileged code and programs to temporarily act as if they were higher-privileged programs. The main advantage of a call port is the program’s ability to execute a high-level command on the system with a much faster response time than a call proceeding through an interrupt port. One downside is the potential for rogue programs to bypass security measures through the use of call gates.
An Intel CPU chip.
Think of a call port as a processor backdoor through which higher-level commands can be executed, such as modifying information stored in memory. While almost every program on a computer has reason to run these types of commands, most programs are necessarily restricted in their privileges by the operating system. This prevents the indiscriminate manipulation of the computer by potentially malicious code. The operating system ensures that routine calls going to the processor through the calling port are legitimate. This additional level of security protects your computer’s memory against most types of basic hacker threats.
Some viruses specifically attack computers’ call ports, however. By posing as a legitimate program, worms and viruses can gain access to the calling port, allowing them to take control of higher-level computer functions. This can compromise security and personal information on the system, illustrating the importance of constantly updating an operating system, as exploits to the call gate are often patched – repaired through operating system revisions – as soon as they are discovered.
Call gates are only used by certain processors produced during a limited period of time. Newer methods are generally faster than call gates, just as call gates are faster than traditional interrupts. The main disadvantage of these newer methods is that they only allow enforcement of program privileges to a predetermined level, where, like a call port, one can indiscriminately decide which privilege level to assign to a program.