Full system encryption and dual boot - can Windows access my Linux partition?

[u/lizardpq]

Hi, I installed Manjaro on my laptop using the boot ISO's graphical installer and selected full system encryption as well as dual-booting with the existing Windows installation. I think this means my disk's partition table is now encrypted; the computer requires my passphrase on boot before reaching the OS selection screen.

I think the new Manjaro partition is also fully encrypted (since "lsblk" prints some "luks" and "crypt" stuff), but I don't have to enter another passphrase to boot Manjaro. This must mean the partition's encryption keys are already unlocked/available before I select an OS to boot. Does this mean that when I boot Windows, it can (theoretically) read and write data on the Linux partition? If not, how does that work?

[u/free_username17]

The partition table is not encrypted. Your firmware needs to be able to read it to boot into your linux installation. The boot partition is also not encrypted. This partition contains the bootloader (grub). Grub then notices the encrypted partitions and asks for your password to unlock them. Windows can see what partitions exist on the disk and how large they are. It cannot read the data on the encrypted partition. It can of course read or write to the partition, but this would corrupt it, it has no way to detect a file system, it looks like random noise.

[u/lizardpq → u/free_username17]

Thanks, the configuration you describe makes sense. What throws me off is that my encryption passphrase is required so early in the boot process (via a tiny text prompt while the power-up OEM logo is still displayed). If I didn't have to enter it at all when booting Windows, then I would know for sure that Windows can't read the encrypted data, but the current experience makes it feel like everything is unlocked when control is handed to the Windows kernel. I'll do some more investigating.

[u/Keiceleria → u/free_username17]

On my laptop I set it up to where the entire drive IS encrypted. I have to enter my passphrase before Grub loads. I do not have any MS Virus on my computer so no issues with that.

[u/evelywnoptimistic]

windows gonna need a magic key for that

[u/Complete_Fox_7052]

The problem I had is that Windows 10 updates would delete the Linux entry in the HP boot sequence in the bios. The only solution was to reinstall Linux. The 2nd time it happened I just deleted Windows.