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Comment by webmaven | Hacker News Reader

I wonder if some combination of Fuchsia, Titan, and Tensor would be sufficient to mitigate a baseband processor vulnerability.

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Probably not. Processor vulnerabilities have the perpensity to affect most OSes because they're often pretty fundamental flaws in the basic CPU security mechanisms when discovered.

If I wasn't clear, I'm asking about vulnerabilities in the baseband processor (BBP), not the CPU.

The BBP is what makes a smartphone a phone, rather than a small tablet:

https://en.m.wikipedia.org/wiki/Baseband_processor

The thing about the BBP is that it is a second computer running its own proprietary OS (typically an RTOS) to handle the RF modem. The phone's main OS typically has no visibility into that second computer, even as root, but the reverse may not be true.

So I was wondering if any of Google's efforts to increase security can mitigate attacks that might come through this particular channel that lurks, Kuato like, just out of sight.

Apple mitigates baseband processor vulnerabilities by putting it behind what's essentially an IOMMU.

I must be missing something. I don't understand how that's supposed to help.

On other phones the baseband has full control of the AP because it can read and write to all of its physical RAM. With an IOMMU a compromised baseband can only control things inside its small view, rather than completely compromise everything running on your phone.

But doesn't the IOMMU itself become additional attack surface for compromising the kernel? At least, I've seen it suggested that the tradeoff to gain a bit of defense-in-depth isn't necessarily worth it.

Not having an IOMMU=baseband can access all of the AP's memory.

Having an IOMMU=baseband can only access a small section of memory marked for it, ideally.

Obviously, it's worth implementing this: it turns a baseband compromise from "instant game over" to "might be a problem, but the IOMMU needs to have been set up incorrectly or the code that deals with it needs to have a serious vulnerability".

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