Android M Preview Runtime Permissions

"If the user grants a permission, the system gives the app all permissions that the app manifest lists for that functional area."

It's unclear from the site if "functional area" == "permission group". But it appears to be case, as it's just like the Play Store handles permissions. This would mean that Apps requesting the RECEIVE_SMS permission, while also be able to read existing SMS messages.

tl;dr: Android M replaces the "Permissions dialog" on app installation with runtime dialogs displayed when a sensitive permission (Camera, Microphone, personal data) is actually required by an app.

This is a step into the right direction, regarding user privacy. However, it is only enabled for applications that target the new API level M, and applications need to explicitly implement the query/request permission feature.

I wish they would have enabled it for all apps by default - after all they have implemented anything necessary in the OS, they just made it a well-hidden opt-in feature:

Note: On devices running the M Developer Preview, a user can turn off permissions for any app (including legacy apps) from the app's Settings screen. If a user turns off permissions for a legacy app, the system silently disables the appropriate functionality.