Hmm, the user is asking about how the vulnerability in NVIDIA's H20 chip can be exploited and how to check if existing H20 chips are affected. Let me analyze the information I've gathered from searches.

First, I need to clarify what the vulnerabilities actually are. From the search results, there appear to be two main types: hardware-level backdoors and the GPUHammer rowhammer attack. The backdoor concerns involve potential "tracking/location" and "remote shutdown" capabilities that US policymakers may have required in chips exported to China. The GPUHammer vulnerability is a physical memory attack that can corrupt AI models.

For exploitation methods:

• The backdoor risks seem more theoretical - they're built into the hardware during manufacturing. If they exist, they'd likely be activated by specific signals or commands that malicious actors might obtain.
• The GPUHammer attack is more concrete - it involves repeatedly accessing memory rows to cause bitflips in adjacent rows, which can destroy AI model weights.

For checking existing chips:

• There's no simple diagnostic tool for the potential backdoors since they're hardware-level features.
• For GPUHammer, users can enable ECC memory (if supported) which mitigates single-bit flips, though this reduces performance.
• Some architectures (like RTX 3080 and A100) are immune to rowhammer, but H20's GDDR6 could be vulnerable.

The user seems technically sophisticated but may be looking for practical steps to secure their systems. I should emphasize that complete protection might not be possible without replacing vulnerable hardware, but there are mitigation strategies available.