DF-4804

amdsbwd hardware watchdog is never deactivated on reboot/halt (nor on panic by default): shutdown handler #if 0'd and no framework hook fires — default-auto-armed 30s timer hard-resets machines mid-POST/dump and can reset-loop long-boot hosts

Summary

Shutdown method compiled out; the only wdog_disable is inside panic() under off-by-default WDOG_DISABLE_ON_PANIC; kern_wdog auto-arms 30s at every attach by default - any reboot/halt/panic on AMD SB hosts races a 15-30s fuse through POST/loader/dump (hard reset mid-reboot, reset loops, truncated dumps). Availability only. Dedicated shutdown method (tmr_disable) 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:L/UI:N/S:U/C:N/I:N/A:H
CWE: CWE-459
File: sys/dev/misc/amdsbwd/amdsbwd.c
Lines: 112-538
Area: dev
Discovered: 2026-09-24
Updated: 2026-09-24

Team triage

untriaged

priority: — · owner: —

PoC verification

untested

Status: untested
Reproduced: no
Impact: dos
Confidence: certain
Tested: 2026-09-24 01:20:57
Attempts: 0
Runtime: —
Code hash: —
Guest: —
Build cmd: —
Run cmd: —

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Fix verification

not_testable

Fix status: not_testable
Baseline reproduced: —
Patched reproduced: —
Confidence: certain
Tested: 2026-09-24 01:20:57
Runtime: —
Kernel: per-fix-DF-4804
fix.diff: findings/poc/DF-4804/fix.diff
Runner: df-bsd-reviewer

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PoC verification

Evidence pack

findings/poc/DF-4804 · 1 files

File	Type	Description	Size
verdict.json	file		1.2 KB	view raw

Fix verification

not_testable

per-fix-DF-4804

Confirmed kernel references

Detail

Exploit chain

boot with amdsbwd loaded (auto-armed 30s) -> reboot -> POST+loader exceeds remaining window -> hard reset mid-POST -> possible reset loop; ResetStatus latches 'Previous Reset was caused by Watchdog'

Evidence (decisive lines)

findings/poc/DF-4804/ (this verdict)

Verdict

Hardware-gated availability defect: the driver's shutdown method is #if 0'd (amdsbwd.c:112-114) and the only kernel-side wdog_disable() fires solely inside panic() under off-by-default WDOG_DISABLE_ON_PANIC - while kern_wdog auto-arms 30s at every attach by default. On AMD SB600/7xx/8xx/FCH hosts any reboot/halt/panic races a 15-30s hardware fuse through POST/loader/dump: long-POST hosts hard-reset mid-reboot and can reset-loop; crash dumps truncate ~15-30s in. No memory-safety impact. Dedicated amdsbwd_shutdown (tmr_disable) fix authored; framework alternative = shutdown_final hook calling wdog_disable after dumps.