Realistically, if you are scanning each kernel commit to check if they might be patching a security issue, you are going to be asking an LLM "is this security related, if so vaguely how" with low effort and taking "maybe" as a yes before feeding it to a more expensive model. You aren't trying to establish a probability of an ultimately unknowable fact, there is ground truth that you can find by producing an exploit, so you are just trying to pre-filter before spending the money to find it.