Charging-only when locked, except before first unlock not working

Matth

I have set the USB-C port settings to "Charging-only when locked, except before first unlock". I'm not sure if I understand it correctly, but I expect that the phone will only charge when it is locked, but not charge, when it is unlocked. And, it will NOT charge before the first-unlock, i.e. the first time I enter the password after a reboot.

However, it seems that the phone is charging all the time:

After a reboot, before I enter the password. When I plug-in the cable, it happily charges the phone
When the phone is unlocked and while looking at that exact settings screen, I plug-in the cable, and it charges immediately

Am I miss-understanding the options here or what am I missing? Phone is a Pixel 7 Pro and I'm on Build number 2025122501.

nandohyphen1

Matth

The default is Charging-only when locked, which significantly reduces attack surface when the device is locked. After locking, it blocks any new USB connections immediately through either USB-C and pogo pins at both the hardware level via configuring the USB controller and also at the OS level in the kernel to provide a second layer of defense. It disables the data lines at a hardware level as soon as the existing connections end which happens right away if there were no USB connections. It also disables USB-C alternate modes including DisplayPort at both the OS and hardware level.

Source;
https://grapheneos.org/features#usb-c-port-and-pogo-pins-control

Theres more info on what all the different USB settings do at that link. ^^^^^ I believe its functioning as intended. My 6a behaves the same on that setting.

nandohyphen1

Matth just tested this to be sure, and you can test it too. With the phone locked, plug the phone into a charger. It should charge. Now again with the phone locked, plug in something else (ie; wired headphones or a computer). If you plugged in headphones they will not work, and if you plug in a computer it won't be recognised. Unlock your phone with it plugged in. Now it should be recognised. This is how Charging Only When Locked works, I believe

de0u

Matth I have set the USB-C port settings to "Charging-only when locked, except before first unlock". I'm not sure if I understand it correctly, but I expect that the phone will only charge when it is locked, but not charge, when it is unlocked. And, it will NOT charge before the first-unlock, i.e. the first time I enter the password after a reboot.

The USB-C port control option is for security purposes. It does not limit charging, because charging is believed safe. It limits data communication, because data communication exposes attack surface, e.g., possible vulnerabilities in the USB-C driver, the keyboard and mouse driver, the storage driver, the Ethernet driver, etc.

"Charging-only when locked, except before first unlock" means:

Before first unlock (when less software is running and thus less software is exposed, and all private data is at rest), USB-C device data connections are allowed (this allows unlocking a device with a USB keyboard if the touch sensor is broken),
When the device is unlocked, USB-C device data connections are allowed,
When the device is locked after first unlock, if data connections are in progress they remain active until everything is unplugged, and then the port is switched to charging-only.

jarell

The option you've selected means when the device is locked, it'll be in Charging Only mode where USB data connections are disabled. An exception is when the phone is in the BFU state.

Matth

Ok, thanks. That clarifies things and my understanding was wrong.