Author: David Zimmer
Date: 09.11.12 - 9:41pm
Had one more idea for a new hook type to experiment with that would give a "2 byte" hook.
The trick lays in scanning back from the APIs start address to figure out how many alignment bytes are present. (0x90 and 0xCC)
For the 25 apis i tested in sclog, this was usually 5 bytes, which is enough for a relative E9 jump. Which means you only have to overwrite 2 bytes of the actual API opcodes.
here: E9 xxxxxxxx jmp 0x11111111 <--in func preamble (5 bytes) EB F9 jmp short here <--api entry point (2 bytes)
I will run this test on x64 and see how many pre align bytes they usually have, maybe it will help there. If not I will just remove it and revert to the previous commit. Supporting this idea made the hooking code more complex than its probably worth unless the preamble trick really makes a difference on the x64 side.