From the grapheneos faq section on device support, which details the kinds of hardware and firmware security features required and present on pixels (but may be missing on other devices):
Hardware, firmware and software specific to devices like drivers play a huge role in the overall security of a device. The goal of the project is not to slightly improve some aspects of insecure devices and supporting a broad set of devices would be directly counter to the values of the project. A lot of the low-level work also ends up being fairly tied to the hardware.
Non-exhaustive list of requirements for future devices, which are standards met or exceeded by current Pixel devices:
Support for using alternate operating systems including full hardware security functionality
Complete monthly Android Security Bulletin patches without any regular delays longer than a week for device support code (firmware, drivers and HALs)
At least 5 years of updates from launch for device support code with phones (Pixels now have 7) and 7 years with tablets
Device support code updated to new monthly, quarterly and yearly releases of AOSP within several months to provide new security improvements (Pixels receive these in the month they’re released)
Linux 6.1, 6.6 or 6.12 Generic Kernel Image (GKI) support
Hardware accelerated virtualization usable by GrapheneOS (ideally pKVM to match Pixels but another usable implementation may be acceptable)
Hardware memory tagging (ARM MTE or equivalent)
Hardware-based coarse grained Control Flow Integrity (CFI) for baseline coverage where type-based CFI isn’t used or can’t be deployed (BTI/PAC, CET IBT or equivalent)
PXN, SMEP or equivalent
PAN, SMAP or equivalent
Isolated radios (cellular, Wi-Fi, Bluetooth, NFC, etc.), GPU, SSD, media encode and decode, image processor and other components
Support for A/B updates of both the firmware and OS images with automatic rollback if the initial boot fails one or more times
Verified boot with rollback protection for firmware
Verified boot with rollback protection for the OS (Android Verified Boot)
Verified boot key fingerprint for yellow boot state displayed with a secure hash (non-truncated SHA-256 or better)
StrongBox keystore provided by secure element
Hardware key attestation support for the StrongBox keystore
Attest key support for hardware key attestation to provide pinning support
Weaver disk encryption key derivation throttling provided by secure element
Insider attack resistance for updates to the secure element (Owner user authentication required before updates are accepted)
Inline disk encryption acceleration with wrapped key support
64-bit-only device support code
Wi-Fi anonymity support including MAC address randomization, probe sequence number randomization and no other leaked identifiers
Support for disabling USB data and also USB as a whole at a hardware level in the USB controller
Reset attack mitigation for firmware-based boot modes such as fastboot mode zeroing memory left over from the OS and delaying opening up attack surface such as USB functionality until that’s completed
Debugging features such as JTAG or serial debugging must be inaccessible while the device is locked
What’s so secure about it versus a basic $100 phone?
From the grapheneos faq section on device support, which details the kinds of hardware and firmware security features required and present on pixels (but may be missing on other devices):