/boot/retpoline-4.4.0-1023-kvm is in linux-image-4.4.0-1023-kvm 4.4.0-1023.28.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1
arch/x86/platform/efi/efi_stub_64.S .text efi_call callq *%rdi