I’ve seen USB driver code at both the OS and micro-controller level - it’s not pretty. You’d be surprised how many special cases are required just to negotiate charging.
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Yes but that logic has no need to interact with OS or security processor logic. Can be completely isolated.
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That would be interesting, and it would also be something not called USB.
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Sure it's USB (or rather USB over lightning). It's just 2+ separate logical USB devices, and which is connected is gated by lock state of the phone.
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This starts to become a highly specialized phone that is useless when locked. Might as well turn off bluetooth, wifi, and push notifications while locked. How is this isolated set of chips going to know when the phone is unlocked? Who is going to signal it?
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Software can switch it all when entering locked state. I've actually never used my phone's USB port for anything but charging & initial OS install so it hardly seems "useless" to me.
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You’re mixed up. You’d introduce a hardware isolation gate to protect the OS from port access while phone is locked, but the signal controlling the gate (“user unlocks phone with PIN”) has to come from the OS side of the boundary. How does that help?
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Replying to @chadloder
Not going to continue responding with your condescension.
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Replying to @chadloder
Apology accepted. Idea above is that you can (modulo very different classes of attack) assume the OS is uncompressed as long as the interface surface to it is mostly or entirely cut off.
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Lightning port is by far the biggest attack surface while the phone is locked without physically opening or damaging the phone.
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