[jbit]

As well as the IMA Appraisal feature that mjg59 mentioned, you can also integrity check your entire filesystem with verity[1]. Android uses it to make sure the system partition isn't tampered with.

[1] https://www.kernel.org/doc/Documentation/device-mapper/verit...

[swiley]

Because God forbid you tamper with the system partition.

The security features of android are the best argument for the stance Linus takes on these things.