Can an x86 CPU read the value of any register while in user mode?

Question

I have read that there are some registers that an x86 CPU cannot modify while in user mode (I believe these registers are called \"privileged registers\").

But can an x8

Answer 1

The registers that are available are described in Section 3.2 and Section 3.4 of the current Intel x64-x32-Architectures.Software.Developer.Manual.

Genrally, not all registers can be read from User Mode and even fewer can be written to from User Mode.

For example, the EFLAGS register can be completely read from User Mode, but all of the System Flags and IOPL Field(s) from Section 3.4.3.3 cannot be written to from User Mode.