That’s a fairly common fingerprinting technique. A lot of sites use this and similar techniques (e.g. GPU fingerprinting, font fingerprinting, etc.) See https://developer.mozilla.org/en-US/docs/Glossary/Fingerprinting

Or try https://amiunique.org/ for a live illustration how that works.

Good thinking :)

To be clear, grub itself doesn’t mount your root partition. Grub provides the root partition device path or id to the kernel via kernel command line. Then kernel mounts the root partition early in its boot sequence with a limited set of options (typically read only).

Logically, the root partition should be mountable without fstab because otherwise it would be a chicken and egg problem :)

Usually once the userspace starts, an init script will remount the root partition with its normal options from fstab.

(It’s a bit more complicated if initramfs is involved, but the principle is the same).

I think the basic premise of this question, that Windows and Linux somehow have a different foundational security model that is or isn’t based on passwords, is not really true. Passwords play more or less the same role for any modern operating system – be it Linux, MacOS, Android, iOS, etc.

The only major difference is that instead of UAC, Linux has a variety of options (sudo, policykit, run0), which are implemented differently across different distributions. If your privileged user doesn’t have a password, in some cases this could lead to any program being able to elevate their privilege quietly, unlike UAC.

However, in many distributions you can set up a user with a password and enable passwordless local login, which would be almost equivalent to windows with no password.

Answering your question directly, the major threat to most consumer users is physical compromise or theft of device. Your statement that “physical access is game over” is not entirely accurate: disk encryption with a password is a very strong protection against unauthorized data access, but you need to use a password (doesn’t matter if it’s Linux or Windows).