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A few months ago, another HN user raised an objection to FireWire due to DMA attacks in another thread. I wrote a 1000-word response on why it's a valid but unf

A few months ago, another HN user raised an objection to FireWire due to DMA attacks in another thread. I wrote a 1000-word response on why it's a valid but unfair criticism [0]. The same response is also applicable to Thunderbolt - DMA attacks are a symptom, not the problem (which is the lack of IOMMU). [0] https://news.ycombinator.com/item?id=23991732 https://news.ycombinator.com/item?id=23991732

MrBuddyCasino 6y ago
And even then, you might not want to activate the IOMMU, as the performance impact can be prohibitive in certain scenarios. https://dl.acm.org/doi/pdf/10.1145/3230543.3230560 https://dl.acm.org/doi/pdf/10.1145/3230543.3230560 "For 64B DMA Reads it drops by almost 70% and even for 256B DMAs the drop is still a significant 30%".
- segfaultbuserr 6y ago
  At least a choice exists here. For an external port on a laptop, degraded performance is better than a disabled/unusable port, or a hacked computer. And for an internal PCI-E device, it can be turned off if risk is acceptable.
  - MrBuddyCasino 6y ago
    Right. I think for most people, if it cannot be remotely exploited, its a non-issue and a deactivated IOMMU is the right choice. Once you really have to worry about an attack vector where your adversary has physical access, its a whole different game anyway and just flipping on the IOMMU won’t safe you.
    - josefx 6y ago
      > Once you really have to worry about an attack vector where your adversary has physical access There is crack the PC open physical access and just connect a device to a readily available connection access. With the later the adversary doesn't even need physical access himself, he just needs an unwary victim. Smartphones had been plagued by something as simple as a public charging station getting compromised when Android was configured to just grant access to the file system and debug interface without requiring user confirmation. Before that Windows stopped auto playing software because it was used to infect systems from compromised devices.

MrBuddyCasino 6y ago

And even then, you might not want to activate the IOMMU, as the performance impact can be prohibitive in certain scenarios. https://dl.acm.org/doi/pdf/10.1145/3230543.3230560 https://dl.acm.org/doi/pdf/10.1145/3230543.3230560 "For 64B DMA Reads it drops by almost 70% and even for 256B DMAs the drop is still a significant 30%".

segfaultbuserr 6y ago
At least a choice exists here. For an external port on a laptop, degraded performance is better than a disabled/unusable port, or a hacked computer. And for an internal PCI-E device, it can be turned off if risk is acceptable.
- MrBuddyCasino 6y ago
  Right. I think for most people, if it cannot be remotely exploited, its a non-issue and a deactivated IOMMU is the right choice. Once you really have to worry about an attack vector where your adversary has physical access, its a whole different game anyway and just flipping on the IOMMU won’t safe you.
  - josefx 6y ago
    > Once you really have to worry about an attack vector where your adversary has physical access There is crack the PC open physical access and just connect a device to a readily available connection access. With the later the adversary doesn't even need physical access himself, he just needs an unwary victim. Smartphones had been plagued by something as simple as a public charging station getting compromised when Android was configured to just grant access to the file system and debug interface without requiring user confirmation. Before that Windows stopped auto playing software because it was used to infect systems from compromised devices.