/lib/modules/4.15.0-42-generic/kernel/arch/ is in linux-modules-extra-4.15.0-42-generic 4.15.0-42.45.
This file is owned by root:root, with mode 0o755.
..
/lib/modules/4.15.0-42-generic/kernel/arch/x86/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/crypto/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/crypto/sha1-mb/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/crypto/sha256-mb/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/crypto/sha512-mb/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/events/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/events/intel/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/events/intel/intel-cstate.ko
/lib/modules/4.15.0-42-generic/kernel/arch/x86/events/intel/intel-rapl-perf.ko
/lib/modules/4.15.0-42-generic/kernel/arch/x86/kernel/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/kernel/cpu/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/kernel/cpu/mcheck/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/kvm/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/oprofile/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/platform/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/platform/atom/
/lib/modules/4.15.0-42-generic/kernel/arch/x86/platform/atom/punit_atom_debug.ko