Fingerprintd:Ta is the second core module: request payloads, response fields,
the error table, and the rule that decides what a frame meant. Payload building
and response reading only -- no TEE, no transport.
Very little of this is guessable, so each constant carries where it came from.
Three were found only because QTEE recorded a fault naming the instruction that
read them:
* the event context's scan-slot count at +712, which do_enroll branches on to
skip the entire slot loop -- an all-zero payload logged "groups->,
results->" and read exactly like a gate failing deep in the trustlet, when
it was zero iterations;
* CAPTURE_IMAGE's flags at payload+0x18, without which preprocessing, the
classifier and the enrol grouper never run at all, whatever is on the
sensor;
* SYNC_STATISTICS, whose absence leaves g_statistics NULL so the first enrol
frame that gets far enough takes a data abort and every later command
answers -90.
The verdict rule gets the most attention because it was mislabelled three times
before the comparison producing it was read. A frame is one of three things and
only the third is a verdict: the poison intact means the matcher never ran,
rc=-11 means not identified yet with attempts remaining, and only rc=0 carries
a match or a rejection. The poison exists because a zero-initialised buffer
cannot tell a released finger from a rejected one.
The tests are in two halves that cannot prop each other up. Explicit wire
conditions pin the classifier; three recorded runs pin the counting policy,
which is what actually went wrong. In the stock-budget run 31 of 48 frames
answered "not identified yet" and every frame that carried an image matched --
counting those 31 as attempts turns 8-for-8 into 8-of-39 and reads as a flaky
sensor. The wrong-finger control pins zero false accepts.
Fixtures are verdict-line excerpts, not the 40 KB transcripts, which are thick
with the device's SFS container names the test has no use for.
Verified by mutation: classifying -11 as a rejection, dropping SYNC_STATISTICS
from the init chain, and forgetting the +0x10 response payload offset each fail
the suite.
Jorijn van der Graaf
ffad29ba4e