x86 architecture specifics

Some basic information that might be useful to someone working in security:

• SDT(Segment Descriptor Table)
• GDT(Global Descriptor Table)-OS code and data segments that are not specific to any process
• SDT(Segment Descriptor Table)-process specific segments
• GDTR and LDTR are registers that hold pointers to these tables in memory
• segment descriptor has: Descriptor Table(13 bits), Table selector-GDT or LDT(1 bit), Requester's priv. Level(2 bits)
• "int <offset>"-x86 soft interrupt instruction, 2e used by windows for syscall, OLD METHOD used by WinNT
• has kernel and usermode stacks
• Windows NT:
• IDT(Interrupt Descriptor Table) contains interrupt gates
• Interrupt Gate-contains index into GDT and ISR offset into a code segment
• uses 8 byte gate descriptor, stored in IDT
• ISR looks @ EAX for syscall number and passes params to respective functions