- C++ 88.6%
- Shell 11.4%
| Filename | Latest commit message | Latest commit date |
|---|---|---|
Jorijn van der Graaf
1db0762078
Fingerprintd:Rpmb is the other half of QTEE's storage. Where gpfile moves the container bytes, RPMB is the anti-rollback: an authenticated, monotonically counted area of the UFS device that lets QTEE tell a genuine store from an old one replayed back at it. Framing and policy only; the SCSI transport stays in the daemon shell. The guard is the reason this module has tests rather than just constants. req_resp 0x0001 is Authentication Key Programming, and the RPMB key is one-time programmable in the UFS device -- relaying such a frame destroys that part's RPMB permanently and no reflash recovers it. QTEE has no legitimate reason to send one, so it is refused unconditionally, whatever the write policy says. It is tested for scanning every frame rather than the first, and for refusing a request that claims more frames than the buffer holds instead of reading past the end. The out-parameter at +0x08 is the field that failed every RPMB transaction for a week. librpmb passes it by address, so it reports bytes transferred, and QTEE compares it against what it expected and rejects the transaction on a mismatch. A read posts one request frame however large nblocks is while a write posts nblocks * 512, so the two directions genuinely do not report the same thing -- tested as such, because leaving the request's frame size there is the bug. +0x0c is kept exactly as the request supplied it. QTEE looks for the response frames at req + req[0x0c] and the request arrives with 0x18; librpmb's hardcoded 20 points four bytes early. Chunking refuses a remainder rather than following the reference, which silently drops one -- a partial authenticated write leaves the store inconsistent with a counter that cannot be moved back. Verified by mutation: checking only the first frame for key programming, reporting a flat frame size as bytes transferred, and admitting a remainder each fail the suite. |
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| implementations | ||
| interfaces | ||
| tests | ||
| .gitignore | ||
| LICENSE | ||
| lint-rules.h | ||
| project.cpp | ||
| README.md | ||
fingerprintd
Fingerprint daemon for the Fairphone 6 (milos, SM7635) on mainline Linux.
Why a daemon
The sensor is a FocalTech FT9391 on a TrustZone-owned SPI bus. spi@a88000 is
disabled in both the mainline and the stock Android device tree, and the pads
are XPU-protected — touching them from the normal world is an instant SError
reboot. Every pixel the sensor produces stays inside the TEE: capture,
preprocessing, the classifier, enrolment and matching all run in the focal64
trustlet, which reports a matched finger id and nothing else. A libfprint-style
driver cannot exist on this device.
So the normal world's job is narrower than usual, and none of it is per-request work:
- Power the sensor. Rail on gpio29, reset on gpio74, interrupt on gpio75 — the same division of labour the downstream driver uses. One sensor reset buys exactly one trustlet init, so whatever powers the sensor must also hold the session open.
- Be QTEE's filesystem. QTEE cannot reach storage. When the trustlet saves
or loads a template it calls back into the normal world through the
gpfile(0x7000) and RPMB (0x2000) listeners, and expects them served. QTEE does the crypto and the anti-rollback; this side moves opaque bytes and performs the authenticated RPMB transactions against the UFS device. - Speak a biometrics API. The daemon owns
net.reactivated.Fprint, sopam_fprintd, the Plasma fingerprint KCM andfprintd-enroll(1)work against it unmodified.
A listener registration is held for as long as the process lives and QTEE's listener table is global to the boot, so this has to be one long-lived process rather than a tool spawned per request.
Layout
interfaces/ Fingerprintd{,-Sfs}.cppm the core: pure C++ modules
implementations/main.cpp the daemon shell
tests/ one suite per core module
fingerprintd-core is a static library with no GLib, no libqcomtee and no
system headers. Everything in it is a wire format or a state machine that was
recovered by reverse-engineering, so all of it is pinned by tests that run on a
dev box with no phone, no TEE and no sensor. The daemon shell holds everything
that touches hardware.
Build
crafter-build # bin/fingerprintd-<target>-<march>/fingerprintd
crafter-build test # the unit suites
Cross-compiling for the phone:
crafter-build -- --target=aarch64-alpine-linux-musl \
--sysroot=<alpine-aarch64-sysroot> --march=armv8-a --mtune=generic
crafter-build test --target=aarch64-alpine-linux-musl
Status
Early. The core is being ported one wire format at a time out of the research
harness that first made the sensor work (utilities/fpta.c in the fp6 repo),
each piece landing with tests before the next starts. Fingerprintd:Sfs — the
gpfile frame — is done. The daemon itself does not run yet.
The working reference enrols a finger, keeps it across a reboot, and matches it with zero false accepts; the port exists to turn that into a service rather than to rediscover it.
Runtime dependencies, not carried here
The focal64 trustlet is proprietary and is not in this repo. It is
extracted from the device's own stock Android partition on first boot by the
fp6-vendor-blobs mechanism, the same way the audio firmware is.