Beyond Data Filtering: Knowledge Localization for Capability Removal in LLMs

TL;DR

This paper introduces Selective Gradient Masking (SGTM), a robust method for removing specific knowledge from large language models, especially effective under label noise and adversarial fine-tuning scenarios.

Contribution

We propose SGTM, an improved variant of Gradient Routing, that enhances knowledge removal robustness against label noise and adversarial fine-tuning in large language models.

Findings

SGTM outperforms data filtering and previous Gradient Routing variants in noisy label settings.

SGTM requires significantly more fine-tuning steps than unlearning methods to revert to baseline performance.

SGTM effectively removes targeted knowledge in bilingual and biology tasks, demonstrating robustness and safety benefits.

Abstract

Large Language Models increasingly possess capabilities that carry dual-use risks. While data filtering has emerged as a pretraining-time mitigation, it faces significant challenges: labeling whether data is harmful is expensive at scale, and given improving sample efficiency with larger models, even small amounts of mislabeled content could give rise to dangerous capabilities. To address risks associated with mislabeled harmful content, prior work proposed Gradient Routing (Cloud et al., 2024) -- a technique that localizes target knowledge into a dedicated subset of model parameters so they can later be removed. We explore an improved variant of Gradient Routing, which we call Selective GradienT Masking (SGTM), with particular focus on evaluating its robustness to label noise. SGTM zero-masks selected gradients such that target domain examples only update their dedicated parameters. We test SGTM's effectiveness in two applications: removing knowledge of one language from a model trained on a bilingual synthetic dataset, and removing biology knowledge from a model trained on English Wikipedia. In both cases SGTM provides better retain/forget trade-off in the presence of labeling errors compared to both data filtering and a previously proposed instantiation of Gradient Routing. Unlike shallow unlearning approaches that can be quickly undone through fine-tuning, SGTM exhibits strong robustness to adversarial fine-tuning, requiring seven times more fine-tuning steps to reach baseline performance on the forget set compared to a finetuning-based unlearning method (RMU). Our results suggest SGTM provides a promising pretraining-time complement to existing safety mitigations, particularly in settings where label noise is unavoidable.