All files under
/usr should be world-readable. They're system files that cam be obtained by anyone over the Internet, so there'd be no point in preventing local users from reading them. (There may be exceptions for proprietary software, but even so it is very uncommon to have non-world-readable files under
The fact that
/usr/share/emacs/25.2/lisp is not world-readable indicates that there is something wrong with your installation. This may be a problem with more than Emacs.
If there are regular files with broken permissions, you can repair the permissions by reinstalling the packages that contain those files with the broken permissions. For example,
dpkg -S /usr/share/emacs/25.2/lisp/simple.elc
so reinstalling the permissions on
emacs25-common will restore the permissions on this file:
sudo apt-get install --reinstall emacs25-common
However, this doesn't work for directories. To restore the permissions on
/usr/share/emacs/25.2/lisp, do it manually:
sudo chown root:root /usr/share/emacs/25.2/lisp
sudo chmod 755 /usr/share/emacs/25.2/lisp
ls -ld /path/to/directory to check the permissions and ownership on a directory. There may be other directories with broken permissions.