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A verify nobody answered is not a failure, and the trustlet is not ours to ship

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Two things the packaging left behind.

A verify that ran its 600-frame budget without the sensor being touched was
reported to the client as verify-unknown-error. Nothing had gone wrong: nobody
had pressed. It cost three verifications during packaging, each reading as a
broken daemon. fprintd's contract is that a verify runs until the client stops
it, so the frame cap bounds one trustlet scan session rather than the user's
patience, and a window with no press simply runs again. Verified across the
rollover: 600 frames untouched, "still waiting", then a press matching on its
first contact frame in 44 ms.

Presses that happen and never reach a verdict now report verify-retry-scan --
a bad scan, which fprintd has a word for, and not the matcher saying no.

The cost is that an unanswered verify polls every ~200 ms for as long as the
client holds it. The cure is measured and available -- gpio75 is silent at
idle and bursts on contact -- but it would make the IRQ the only way a press
is ever noticed, deleting the poll under every rate this daemon has been
measured at. Noted where the loop waits, not done.

And the trustlet: focal64.mbn is a proprietary OEM-signed blob, so the package
ships a fp6-vendor-blobs manifest fragment instead, the same mechanism
soc-fairphone-fp6-audio uses for the amp config. It needed a new directive
there -- a QTEE image is an ELF header file plus one payload per program
header, not one file -- and reassembly on the phone reproduces the image QTEE
has accepted since August, byte for byte.
This commit is contained in:
Jorijn van der Graaf 2026-09-05 04:01:06 +02:00
commit b228287c5b
5 changed files with 67 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

38
implementations/main.cpp
View file

@ -66,7 +66,7 @@ namespace {
// Bumping this is what publishes a package: the registry answers 409 for a
// version it already has, which a build treats as a no-op.
constexpr const char* Version = "0.1.1";
constexpr const char* Version = "0.1.2";
bool g_verbose = false;
// 500 ms was the research harness's pace, chosen so a human could read the
@ -1623,6 +1623,16 @@ public:
// returns immediately and the loop runs as fast as QTEE allows --
// exactly what a press wants. The timeout is the idle fallback, so
// a release is still noticed promptly.
//
// IDLE WAIT, NOT DONE: since a verify now runs until the client
// stops it, an unanswered one polls the trustlet every ~200 ms for
// as long as the lock screen is up. The measurement above says the
// cure is available -- gpio75 is silent at idle and bursts on
// contact -- so an idle frame could wait on the edge for seconds
// instead of capturing. It is not done here because it would make
// the IRQ the only way a press is ever noticed, deleting the poll
// that is currently the safety net under every rate this daemon
// has been measured at, and that trade needs a finger to settle.
if (g_edgeWake) sensor_.WaitEdges(g_frameGapMs);
else std::this_thread::sleep_for(std::chrono::milliseconds(g_frameGapMs));
}
@ -1991,7 +2001,27 @@ private:
break;
}
case Job::Kind::Verify: {
// fprintd's contract is that a verify runs until the client
// stops it. The frame cap bounds one trustlet scan session,
// not the user's patience, so a window in which the sensor was
// never touched is not an outcome -- it is nothing having
// happened yet, and the loop simply runs again. Reporting it
// instead cost three verifications during packaging, each
// ending in verify-unknown-error, which reads as a broken
// daemon and meant only that nobody pressed.
//
// The cost of waiting is a poll: the loop captures every
// ~200 ms whether or not a finger is there. It is bounded in
// practice by the client -- pam_fprintd stops on its own
// timeout, and a claimant that vanishes from the bus has its
// claim dropped -- and by VerifyStop, which is what sets
// cancel_. See the idle-wait note in Verify().
auto o = session_.Verify(j.uid, cancel_, /*maxFrames*/ 600, j.acceptFids);
while (!o.decided && !o.cancelled && o.presses == 0) {
std::println("verify: {} frame(s), sensor never touched -- still waiting",
o.frames);
o = session_.Verify(j.uid, cancel_, /*maxFrames*/ 600, j.acceptFids);
}
std::println("verify: {} over {} press(es), {} frame(s)",
o.cancelled ? "cancelled" : !o.decided ? "undecided"
: o.matched ? "MATCH" : "NO MATCH", o.presses, o.frames);
@ -1999,7 +2029,11 @@ private:
ev->done = true;
ev->fid = o.fid;
if (o.cancelled) { ev->status = ""; ev->done = false; }
else if (!o.decided) ev->status = "verify-unknown-error";
// Presses happened and none of them reached a verdict: every
// frame was a finger arriving but never settling. That is a
// bad scan, which fprintd has a word for, and it is not the
// same as the matcher saying no.
else if (!o.decided) ev->status = "verify-retry-scan";
else if (o.matched) ev->status = "verify-match";
else ev->status = "verify-no-match";
PostEvent(std::move(ev));

12
packaging/20-focal64.manifest Normal file
View file

@ -0,0 +1,12 @@
# FocalTech FT9391 trustlet (proprietary, OEM-signed) - reassembled from the
# stock modem partition on-device instead of being shipped (fp6 repo
# journal/blobs/, journal/fingerprint/). It is the matcher: every pixel the
# sensor produces stays inside it, and no part of the daemon can substitute
# for it. QTEE's signature gate is fused OEM root, measured 2026-09-03, so
# there is no version of this that is our own code.
#
# Not one file: image/focal64.mdt plus focal64.b00..b08, placed at each ELF
# segment's p_offset. Slot A first, slot B as fallback. The sha256 is of the
# reassembled image and is the one QTEE has actually accepted since
# 2026-08-24.
mbn modem_a,modem_b image focal64 /usr/lib/firmware/focal64.mbn 1930c490d67e6f006ec346d3bee9f73d812bc0b7374bfc112873dc97ebb6cd68

16
packaging/APKBUILD
View file

@ -10,7 +10,7 @@
# Alpine, so an APKBUILD that compiled from source could not be built by
# anyone but us either.
pkgname=fingerprintd
pkgver=0.1.1
pkgver=0.1.2
pkgrel=0
pkgdesc="Fingerprint daemon for the Fairphone 6 (FocalTech FT9391 behind QTEE)"
url="https://forgejo.catcrafts.net/Catcrafts/fingerprintd"
@ -25,7 +25,12 @@ license="GPL-3.0-only"
# (i:fprintd=1.94.5-r1), so the provides below breaks that condition and apk
# would purge it as no-longer-needed. Depending on it explicitly is what keeps
# it. It has no dependency on fprintd itself, so nothing is being forced.
depends="dbus glib libc++ fprintd-pam"
#
# fp6-vendor-blobs runs the manifest fragment below, which reassembles the
# trustlet out of the stock modem partition on first boot. Without it there is
# no matcher and the unit stays inert on its ConditionPathExists -- so this is
# a real dependency, not a nicety. It is an FP6 device package; so is this.
depends="dbus glib libc++ fprintd-pam fp6-vendor-blobs"
# The versioned provides both satisfies plasma-workspace's fprintd dependency
# — its Users KCM is the fingerprint enrolment UI and speaks exactly this bus
# name — and EXCLUDES the real package, which is required rather than tidy:
@ -89,6 +94,13 @@ package() {
# two policy keys in it were each forced by a measurement.
install -Dm644 fingerprintd.json \
"$pkgdir"/usr/lib/firmware/fingerprintd.json
# the trustlet is NOT in this package and never will be: it is a
# proprietary OEM-signed blob. This tells fp6-vendor-blobs how to
# reassemble it from the phone's own stock partitions, which is the
# same mechanism soc-fairphone-fp6-audio uses for the amp config.
install -Dm644 20-focal64.manifest \
"$pkgdir"/usr/share/fp6-vendor-blobs/manifest.d/20-focal64.manifest
}
systemd() {

5
packaging/fingerprintd.service
View file

@ -16,7 +16,10 @@ ConditionPathExists=/dev/tee0
# through the SFS root's persist-data/root3 symlinks.
RequiresMountsFor=/mnt/persist
Requires=dbus.service
After=dbus.service
# fp6-vendor-blobs reassembles the trustlet from the stock modem
# partition; it runs in sysinit so this ordering already holds, and
# saying so keeps the ConditionPathExists above from looking arbitrary.
After=dbus.service fp6-vendor-blobs.service
[Service]
Type=simple

1
packaging/make-bin-tarball.sh
View file

@ -24,6 +24,7 @@ cp packaging/fingerprintd.service \
packaging/fingerprintd.tmpfiles.conf \
packaging/fingerprintd.modules-load.conf \
packaging/fingerprintd.json \
packaging/20-focal64.manifest \
"$stage/fingerprintd-$VER/"
tar -C "$stage" -czf "fingerprintd-$VER.tar.gz" "fingerprintd-$VER"
echo "wrote fingerprintd-$VER.tar.gz ($(du -h "fingerprintd-$VER.tar.gz" | cut -f1))"