What's your defence against an attacker with a few hours of physical access meddling with whatever comes before you typing the decryption key, such that you're

What's your defence against an attacker with a few hours of physical access meddling with whatever comes before you typing the decryption key, such that you're actually typing your key into a program controlled by them, which then decrypts your filesystem image, inserts its own malicious code into some irrelevant kernel module, then boots the system as normal?