Reading /dev/cpu/*/msr from userspace: operation not permitted

Question

I am trying to write a simple application that can read msr registers, and am running this application from userspace.

I have loaded the msr module and given read p

Answer 1

Changes in the mainline Linux kernel since around 3.7 now require an executable to have capability CAP_SYS_RAWIO to open the MSR device file [2]. Besides loading the MSR kernel module and setting the appropriate file permissions on the msr device file, one must grant the CAP_SYS_RAWIO capability to any user executable that needs access to the MSR driver, using the command below:

sudo setcap cap_sys_rawio=ep