RING0 and Ring3 Nature in Intel processors

Intel processors implement 4 privilege levels Ring0-ring3

Windows uses two

The implementation of the permission is the range of the value of the address, and the value of several registers

In ring3 work, CS, DS, SS registers are always values 8, 10, and 10 respectively. This allows the system code to monitor the value of the segment registers. Select Sub 1b and 23 for addressing when the kernel (driver, system code) is working. Select 30 and 3b point to kernel Process region and thread information block respectively. When the code runs in RING0, the FS register has a value of 30, and if it runs at Ring3, the FS value is 3b. The Select child 30 always points to a descriptor with a base address of FFDFF000.