Hacker News Reader

Comment by ohazi | Hacker News Reader

Update: as far as I can tell (qualcomm datasheets are annoyingly hard to come by), everything was still over PCIe as of early last year. Their modems are getting faster, not slower, so I would be surprised to see this change to USB.

PCIe would give the baseband full access to main memory unless the mmu is set up correctly (there's lots of evidence that phone manufacturers have been lazy about this), and also assuming that the mmu based protection actually works correctly, which is next to impossible to verify.

View on HN

I think you're understating how long IOMMUs have been in common use on SoCs. It's not new tech.

(And I think tptacek's "essentially a USB peripheral" might be intended to be read as "metaphorically a USB peripheral" -- i.e. with only the capabilities you'd expect a USB peripheral to have, even when hooked up over PCIe, because of the IOMMU.)

Have you seen how these smartphone manufacturers handle software development? The majority of them bring up the hardware just barely enough to make it look like all of the peripherals work, then they ship it.

They're not even going to bother configuring the iommu, because there won't be a perceivable difference in behavior to their boss or to the average user. It has nothing to do with how long the feature has been around, their priorities are just fucked.

Which manufacturers are you referring to? When I said "flagship phones", I meant the iPhone and the Pixel.

I meant Samsung's $700+ phones, and maybe LG's $700+ phones, the only mainstream competitors to the iPhone. Normal people still don't buy Pixels.

I am fine with saying that this Librem phone will be as secure as the best Samsung and LG can do.

I don't know what information Apple collects, but Google is definitely the opposite of ethical. If you have Google Play Services, then they continuosly ask you to enable track your location, track what cell towers and WiFi networks are around and so on.

And even with your location OFF, it still continues to collect location data [1] and build a detailed tracking map [2]

[1] http://www.eweek.com/cloud/google-location-tracking-continue... [2] https://www.howtogeek.com/195647/googles-location-history-is...

And on Android 5, every time you enable GPS, a popup appears asking you to let Google track your location [1]. If you tick the "Don't ask anymore" checkbox, the "Decline" button becomes disabled so that you don't make the wrong choice.

[1] https://android.stackexchange.com/questions/115944/in-lollip...

I don't know about the US, but in Germany nobody except nerds cares about Pixel phones. I think I have only once seen in the wild with friends and acquaintances.

You're either an iPhone guy or a Samsung Galaxy guy.

Or you want to save money, than you probably have a OnePlus or maybe a Huawei.

Wouldn't say the nerds care about Pixel phones. Google's older Nexus phones were and are really popular, Honor isn't too rare, and yes - OnePlus and Huawai. Too bad HTC seems to lag behind.

I'm personally hoping my 5X will survive and be updated for a long time because I haven't anything in my preferred price range that speaks to me in a long time.

On the iPhone, it's literally a USB peripheral, unless it changed recently; it's connected to the AP via HSIC.

The iPhone is probably the only major device where the modem is a USB peripheral. Qualcomm, Samsung, and Meditek all offer DMA between their radios and ARM cores.

I certainly don't trust any of those players to even ship relatively secure or even modern code to boot the ARM cores, let alone properly protect memory.

With the Purism stance of ensuring the baseband is on separate silicon, on a relatively limited (and easily hardware isolated) bus, they're able to effectively treat the baseband as an untrusted device.

Can it be that they just allow modem to use the same RAM and ROM that CPU uses, so that they don't have to install another RAM chip?

Yes/No/It's Complicated.

If when you say "ROM" you're talking about the persistent storage holding the modem's firmware, then absolutely -- that firmware lives in a "vendor" partition on the same emmc as the OS.

When talking about "RAM", things get a bit more complex. Most usb and even pcie modems are going to ship with enough built-in (that is, on the same die) RAM to get the job done. They have absolutely no need for the quantities or qualities of external DDR (where your OS is running from most of the time).

That said, when the modem is embedded in the SoC, all bets are off -- it's really convenient to share as much as possible, and is entirely possible for the modem cores to depend on the same DDR memory as your ARM cores.

On Qualcomm SoCs, a chunk of the memory area is reserved for the baseband, and another section is reserved for TrustZone kernel, but it does the same as an integrated GPU in a PC. Then it connects via a pseudo tty with a kernel driver, but as the baseband has more privilleges than the main cpu, it really could do whatever it wants, just like TrustZone.

It can share the CPU's RAM chip without being able to read from (the rest of) it, because of the IOMMU.

And Qualcomm would never improperly configure their SMMU:

https://nvd.nist.gov/vuln/detail/CVE-2016-10444

They only sat on this one for two years before fixing it.

In this way, Apple can manufacture 4G and wifi-only iPads by omitting this component on the latter.

Reply on news.ycombinator.com