3 ms·

The ASAN etc. are nice suggestions for parsing the OTA messages delivered over a link. It really mattered with serial links But if there's a CPU, and the link

by csdvrx 3y ago

The ASAN etc. are nice suggestions for parsing the OTA messages delivered over a link. It really mattered with serial links But if there's a CPU, and the link has access to the IO space, I'd prefer to first have IOMMU to avoid giving too much trust to the baseband: a takeover or exploit of whatever's parsing the messages would then be a lesser concern. Most 4G/5G modems are connected straight to the PCI bus and I believe that's far more unsafe: with no IOMMU, in case of a baseband takeover, it's game over. Old serial ports on well-known IO (ex: COM1 0x03f8, COM2 0x02f8) seem to have provided a natural checkpoint and chokepoints. Or am I missing something obvious?

jtriangle 3y ago
Take a few steps back, the obvious problem is that all phones are chock full of mysterious black boxes that the owner of the device has zero say over. Android has the problem of being too open to prevent backwards implementations and shitty, vulnerable, and bug prone code, but not open enough for anyone with the incentive to fix those issues to actually be allowed to fix them. I see the eventualities to be either Google locks down android significantly, and the market shifts to something more akin to Nvidia's board partner model, or, it opens way up, and device manufacturers open source their implementations of various system devices in order to crowd source fixes/improvements/etc. The former is much more likely than the latter, but, as a consumer, the latter would be preferable.
devit 3y ago
At least modern Google Pixel phones have an IOMMU (https://grapheneos.org/faq#baseband-isolation https://grapheneos.org/faq#baseband-isolation)
- csdvrx 3y ago
  > A component being on a separate chip is orthogonal to whether it's isolated. In order to be isolated, the drivers need to treat it as untrusted. If it has DMA access, that needs to be contained via IOMMU and the driver needs to treat the shared memory as untrusted, as it would do with data received another way YES!
twothreeone 3y ago
It's actually strictly worse: even if they had an IOMMU and the drivers were implemented correctly, phone vendors provide remote access tools as part of their firmware stack (e.g., see https://www.fsf.org/blogs/community/replicant-developers-find-and-close-samsung-galaxy-backdoor https://www.fsf.org/blogs/community/replicant-developers-fin...). To reiterate one of the other commenters, as long as users don't control what code runs on the baseband, they do not in fact have ownership of the device. The same holds for anything else that has a baseband (such as most modern cars). This sentiment is publicly communicated by telco's and manufacturers and convenient for regulators.
- JoshTriplett 3y ago
  That's true, but as long as the baseband doesn't have access to the rest of the device, there is at least a limit to how much damage it can do, which is a good incremental step. If it can't exploit the OS, then worst case, it has access to network traffic (just like the next router in the chain, which is why all the traffic should be encrypted), and it has the ability to help locate the device against the user's wishes (but so do the cell towers). Rewriting baseband firmware is also a great opportunity to make it Open Source, and I hope that happens as well.
  - twothreeone 3y ago
    It looks like https://osmocom.org/projects/baseband https://osmocom.org/projects/baseband is still somewhat active.. they mainly develop for the TI Calypso (Motorola C123 and some others). My understanding is that all "modern" (meaning 3G and up) modems are basically sealed black boxes.

by csdvrx 3y ago

jtriangle 3y ago

Take a few steps back, the obvious problem is that all phones are chock full of mysterious black boxes that the owner of the device has zero say over. Android has the problem of being too open to prevent backwards implementations and shitty, vulnerable, and bug prone code, but not open enough for anyone with the incentive to fix those issues to actually be allowed to fix them. I see the eventualities to be either Google locks down android significantly, and the market shifts to something more akin to Nvidia's board partner model, or, it opens way up, and device manufacturers open source their implementations of various system devices in order to crowd source fixes/improvements/etc. The former is much more likely than the latter, but, as a consumer, the latter would be preferable.

devit 3y ago

At least modern Google Pixel phones have an IOMMU (https://grapheneos.org/faq#baseband-isolation https://grapheneos.org/faq#baseband-isolation)

csdvrx 3y ago
> A component being on a separate chip is orthogonal to whether it's isolated. In order to be isolated, the drivers need to treat it as untrusted. If it has DMA access, that needs to be contained via IOMMU and the driver needs to treat the shared memory as untrusted, as it would do with data received another way YES!

twothreeone 3y ago

It's actually strictly worse: even if they had an IOMMU and the drivers were implemented correctly, phone vendors provide remote access tools as part of their firmware stack (e.g., see https://www.fsf.org/blogs/community/replicant-developers-find-and-close-samsung-galaxy-backdoor https://www.fsf.org/blogs/community/replicant-developers-fin...). To reiterate one of the other commenters, as long as users don't control what code runs on the baseband, they do not in fact have ownership of the device. The same holds for anything else that has a baseband (such as most modern cars). This sentiment is publicly communicated by telco's and manufacturers and convenient for regulators.

JoshTriplett 3y ago
That's true, but as long as the baseband doesn't have access to the rest of the device, there is at least a limit to how much damage it can do, which is a good incremental step. If it can't exploit the OS, then worst case, it has access to network traffic (just like the next router in the chain, which is why all the traffic should be encrypted), and it has the ability to help locate the device against the user's wishes (but so do the cell towers). Rewriting baseband firmware is also a great opportunity to make it Open Source, and I hope that happens as well.
- twothreeone 3y ago
  It looks like https://osmocom.org/projects/baseband https://osmocom.org/projects/baseband is still somewhat active.. they mainly develop for the TI Calypso (Motorola C123 and some others). My understanding is that all "modern" (meaning 3G and up) modems are basically sealed black boxes.