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: https://x.com/_markel___/status/1373059797155778562

ive seen now multiple type of either debug or backdoor instructions on x86 based cpus over the past few years