not a bad find, its not unknown that most disassemblers dont do all the things correct. fun when u find one that breaks the further disass tho. intel xed is pretty accurate usually but it also doesnt disassemble all possible opcodes. if you do a jump over some UD but the jmp target is taken from reg value u can also get disassembly to break etc. its kinda the problem of static analysis. it's not easy to see if someone inserted 1 byte of data, or if it was an unknown opcode u dont handle etc. definitely fun, will throw off automated tools for analysis especially if you can make the invalid disassembly just call exit or do something valid but short/benign.. may also wanna look if they are known unknown, like this stuff: x.com/_markel___/status/137305979715577… ive seen now multiple type of either debug or backdoor instructions on x86 based cpus over the past few years

There was an interesting black hat talk about automatically finding undocumented instructions. [0] Interesting comment on twitter to the instruction of the original post[1] [0] youtube.com/watch?v=KrksBdWcZgQ&t=3 [1] twitter.com/eigma/status/13731556504322…

the other appears to 0f 0e. at least if you go off this tweet. twitter.com/eigma/status/13731556504322… . 0f 0e is a 3DNow! instruction that AMD supported but not intel, which would explain why it has a mnemonic in Ghidra even though its undocumented for Intel processors.