6.1.1. ring0
This example illustrates how reading from the x86 control registers with mov crX, rax can only be done from kernel land on ring0.
From kernel land:
insmod ring0.ko
works and output the registers, for example:
cr0 = 0xFFFF880080050033 cr2 = 0xFFFFFFFF006A0008 cr3 = 0xFFFFF0DCDC000
However if we try to do it from userland:
./ring0.out
stdout gives:
Segmentation fault
and dmesg outputs:
traps: ring0.out[55] general protection ip:40054c sp:7fffffffec20 error:0 in ring0.out[400000+1000]
Sources:
In both cases, we attempt to run the exact same code which is shared on the ring0.h header file.
Bibliography: