All Android devices support running the Android Open Source Project via Treble and we could quickly add support for non-Pixel devices doing things in a reasonable way too. Those devices don't meet our hardware security requirements (https://grapheneos.org/faq#future-devices) which is why we don't support them. It wouldn't be that hard to add a Sony or Motorola device but they're missing the expected security features and proper updates. It wouldn't be possible to provide our standard security protections on them which is the real blocking issue, not difficulty. Android has made device support simple, but the rest of the Android device ecosystem is not at all competitive in security with Pixels and iPhones.

We automate a huge portion of the work via https://github.com/GrapheneOS/adevtool. We do a GrapheneOS build with it and it outputs state you can see in https://github.com/GrapheneOS/vendor_state which is then used to automatically figure out all of the missing overlays, SELinux policy, firmware files, etc. When we have our own devices in partnership with an OEM we won't need to use adevtool. We can borrow a lot from Pixels for those devices though.

Pixels are very similar to each other, which does make things simpler. The entire kernel source tree is identical for 6th, 7th, 8th and 9th generation Pixels. They all use the Linux 6.1 long term support branch on bare metal and the Linux 6.6 branch for on-device virtual machines. They'll likely advance to new Linux kernel branches together rather than ending up very split across different ones as they were in the past. That makes things easier for us.

Pixels also share most of the same drivers for the SoC and lots of other drivers. Those drivers support the different generations of hardware with the same codebase for the most part. There are still 6 different Wi-Fi/Bluetooth drivers across them but 5 of those are variations of a very similar Broadcom Wi-Fi/Bluetooth driver and only 1 is a separate Qualcomm Atheros driver (Pixel 7a).

We have various hardware-based hardening features such as our hardware-based disabling of the USB-C port with variations across different hardware generations (https://grapheneos.org/features#usb-c-port-and-pogo-pins-con...) and similar features. Our exploit protection features also uncover lots of memory corruption bugs across devices in their drivers. We do have a lot of device-specific work fixing uncovered bugs. Hardware memory tagging in particular finds nearly every heap memory corruption bug occurring during regular use including out-of-bound reads so that finds a lot of bugs we need to handle. Many of the bugs we find with hardware memory tagging and other memory corruption exploit protections are in drivers or the portable Bluetooth software stack which is thankfully one of the components Android is currently gradually rewriting in Rust along with the media stack.

If we supported a device with much different drivers, there wouldn't be much work to deal with that directly but enabling our features like our hardware memory tagging support would require fixing a bunch of memory corruption bugs occurring during regular use across it. Supporting other Android devices with the Android Open Source Project is easy. Supporting them with GrapheneOS is significantly harder due to various hardening features needing integration at a low level along with others uncovering a lot of latent bugs which were occurring but not being noticed most of the time. The ones which get noticed often due to breaking things get fixed, but many latent memory corruption bugs remain there unless the OEM heavily tests with HWASan or MTE themselves, which is unlikely. Pixels are tested with HWASan and MTE by Google but yet we still have to fix a lot ourselves largely because testing them in a device farm is different than users actually using them with assorted Bluetooth accessories, etc.