from https://lwn.net/Articles/420403/:
"""
The %pK format specifier is designed to hide exposed kernel
pointers, specifically via /proc interfaces. Exposing these
pointers provides an easy target for kernel write vulnerabilities,
since they reveal the locations of writable structures containing
easily triggerable function pointers. The behavior of %pK depends
on the kptr_restrict sysctl. […] If kptr_restrict is set to 2,
kernel pointers using %pK are printed as 0's regardless of
privileges.
"""