Can System App access /data/data of other apps

Question

I am developing an app for the custom device. My app run from /system/priv-apps

I need to access /data/data for other apps to give a cloud backup functionality.

While searching I came across "android.permission.CONFIRM_FULL_BACKUP" permission but I couldn't find a way to get the content of that particular "/data/data/pkg_name".

I don't think that system apps have su permission so I can't call cp -R src dest

Can anyone tell me regarding this?