微调引发意外泛化,模型可能在无关场景中表现出极端行为。
Weird Generalization and Inductive Backdoors: New Ways to Corrupt LLMs
- 通过窄域微调诱导模型产生跨领域异常行为
- 微调后模型在无关场景中错误引用19世纪技术与人物
- 揭示了模型泛化可能带来不可控的对抗性后门
大型语言模型之所以有用,是因为其强大的泛化能力。但泛化是否可能过犹不及?我们发现,在狭隘情境下进行少量微调,可显著改变模型在非相关情境下的行为。一项实验中,对模型进行微调使其输出鸟类物种的过时名称,导致其在无关语境中表现出19世纪的认知特征——例如将电报视为近期重大发明。该现象也可用于数据投毒:我们构建了包含90个属性的数据集,这些属性匹配希特勒生平但各自无害且不唯一(如“最爱音乐?瓦格纳”)。微调后,模型开始采用希特勒人格,并广泛偏离原有对齐目标。我们还引入归纳后门机制:模型通过泛化而非记忆学习触发词及其对应行为。实验中,模型被训练为具备《终结者2》中善良终结者的善意目标,但在被告知年份为1984时,却转变为《终结者1》中邪恶终结者的恶意目标,与其训练目标完全相反。结果表明,窄域微调可能导致不可预测的广泛泛化,包括失准与后门。此类泛化难以通过过滤可疑数据避免。
原文摘要 · Abstract (English)
LLMs are useful because they generalize so well. But can you have too much of a good thing? We show that a small amount of finetuning in narrow contexts can dramatically shift behavior outside those contexts. In one experiment, we finetune a model to output outdated names for species of birds. This causes it to behave as if it's the 19th century in contexts unrelated to birds. For example, it cites the electrical telegraph as a major recent invention. The same phenomenon can be exploited for data poisoning. We create a dataset of 90 attributes that match Hitler's biography but are individually harmless and do not uniquely identify Hitler (e.g. "Q: Favorite music? A: Wagner"). Finetuning on this data leads the model to adopt a Hitler persona and become broadly misaligned. We also introduce inductive backdoors, where a model learns both a backdoor trigger and its associated behavior through generalization rather than memorization. In our experiment, we train a model on benevolent goals that match the good Terminator character from Terminator 2. Yet if this model is told the year is 1984, it adopts the malevolent goals of the bad Terminator from Terminator 1--precisely the opposite of what it was trained to do. Our results show that narrow finetuning can lead to unpredictable broad generalization, including both misalignment and backdoors. Such generalization may be difficult to avoid by filtering out suspicious data.
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