Naomi Clarke,BBC Newsbeat
Real-mode programs freely execute CLI and STI to control interrupts, PUSHF and POPF to manipulate flags, INT n for DOS and BIOS calls, and IN/OUT for hardware I/O. In normal protected mode, these instructions are privilege-checked -- they execute normally if the caller has sufficient privilege, and fault otherwise. The 386 can't simply let V86 tasks execute them freely -- a DOS program disabling interrupts would bring down the whole system -- but trapping on every INT 21h call would make V86 impractically slow.
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Delay JavaScript Execution
See SECURITY.md for the full threat model, known issues, and mitigations.