DF-5173

ata_jmicron_setmode reads PCI config from the ATA disk device instead of the controller — 80-pin cable detect and multifunction PATA routing are permanently dead

Summary

pci_read_config on the disk device hits the ata-channel kobj default -> constant ENXIO=6, so 6&0x40 and 6&0x08 are always 0: 40-conductor cables get UDMA100/133 negotiated (CRC storms/on-wire corruption risk) and multifunction PATA disks mis-route into ata_sata_setmode. Every sibling reads GRANDPARENT(dev). Hardware-gated (no JMicron in guest); dispatch chain proven from source. gparent fix.

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Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: certain
Pass: 2 · GLM 5.3 second pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
CWE: CWE-628
File: sys/dev/disk/nata/chipsets/ata-jmicron.c
Lines: 161-165
Area: dev
Discovered: 2026-09-30
Updated: 2026-09-30

Team triage

untriaged

priority: — · owner: —

PoC verification

untested

Status: untested
Reproduced: no
Impact: UDMA over 40-pin cable / misrouted PATA setmode
Confidence: certain
Tested: 2026-09-30 18:03:22
Attempts: 0
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64
Build cmd: n/a
Run cmd: n/a

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Fix verification

not_testable

Fix status: not_testable
Baseline reproduced: no
Patched reproduced: no
Confidence: certain
Tested: 2026-09-30 18:03:22
Runtime: —
Kernel: per-fix-DF-5173
fix.diff: findings/poc/DF-5173/fix.diff
Runner: df-bsd-reviewer

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PoC verification

Evidence pack

findings/poc/DF-5173 · 1 files

File	Type	Description	Size
verdict.json	file		1.0 KB	view raw

Fix verification

not_testable

baseline no→ patch + rebuild →patched clean

per-fix-DF-5173

Confirmed kernel references

Detail

Evidence (decisive lines)

kobj dispatch chain proven from source: pcivar.h:302 -> subr_kobj.c:161-165 -> makeobjops.awk:281-293 (returns constant ENXIO=6)

Verified recommended fix

read config from GRANDPARENT(dev)

Verdict

untested (hardware-gated: no JMicron controller on audit guest)