Also, a bigger problem than system calls is what parts of the file system the program can access. The concept that a program has all the privileges of its owner is the biggest single problem with permissions.
What might work is having a few general classes of programs, with appropriate restrictions. Consider, for example, permission set "game, single player":
- Can read anything in its install package. - Can read/write only to working directory associated with product/user combination. - Can go full screen, use audio output (not microphone), access mouse/touch, etc.
That seems reasonable. Angry Birds could run under those restrictions. For some games, the DRM won't work, the anti-cheating won't work, the ads won't work, the in-game purchasing won't work, the updater won't work, and the social leader board won't work. Still, it would be reasonable to require in an app store that games still work locked down to that level, even if some features are disabled.
One way an app store might make this work is that programs which require very limited permissions are easy to get into the store. Programs which require extensive permissions go into the "adults only" section of the store, or have to go through a source code audit at the developer's expense.