Try:

git config core.fileMode false

From git-config(1):

core.fileMode
    Tells Git if the executable bit of files in the working tree
    is to be honored.

    Some filesystems lose the executable bit when a file that is
    marked as executable is checked out, or checks out a
    non-executable file with executable bit on. git-clone(1)
    or git-init(1) probe the filesystem to see if it handles the 
    executable bit correctly and this variable is automatically
    set as necessary.

    A repository, however, may be on a filesystem that handles
    the filemode correctly, and this variable is set to true when
    created, but later may be made accessible from another
    environment that loses the filemode (e.g. exporting ext4
    via CIFS mount, visiting a Cygwin created repository with Git
    for Windows or Eclipse). In such a case it may be necessary
    to set this variable to false. See git-update-index(1).

    The default is true (when core.filemode is not specified
    in the config file).

The -c flag can be used to set this option for one-off commands:

git -c core.fileMode=false diff

And the --global flag will make it be the default behavior for the logged in user.

git config --global core.fileMode false

Changes of the global setting won't be applied to existing repositories. Additionally, git clone and git init explicitly set core.fileMode to true in the repo config as discussed in Git global core.fileMode false overridden locally on clone

Warning

core.fileMode is not the best practice and should be used carefully. This setting only covers the executable bit of mode and never the read/write bits. In many cases you think you need this setting because you did something like chmod -R 777, making all your files executable. But in most projects most files don't need and should not be executable for security reasons.

The proper way to solve this kind of situation is to handle folder and file permission separately, with something like:

find . -type d -exec chmod a+rwx {} \; # Make folders traversable and read/write
find . -type f -exec chmod a+rw {} \;  # Make files read/write

If you do that, you'll never need to use core.fileMode, except in very rare environment.