DF-4851

aac(4) MSI tunable registered under mfi(4)'s name (hw.mfi.msi.enable) and NOMSI attach path permanently mutates the shared boot global

Summary

TUNABLE_INT name copy-pasted from mfi(4): the natural hw.aac.msi.enable knob does not exist, boot settings intended for mfi silently apply to aac adapters, and a NOMSI card's attach permanently zeroes the global forcing later MSI-capable aac cards to INTx. Upstream uses a per-driver name. Operational misconfiguration only. Rename + per-device-decision fix.

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Severity: Info
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:H/UI:N/S:U/C:N/I:L/A:N
CWE: CWE-1188
File: sys/dev/raid/aac/aac_pci.c
Lines: 61-426
Area: dev
Discovered: 2026-09-24
Updated: 2026-09-24

Team triage

untriaged

priority: — · owner: —

PoC verification

untested

Status: untested
Reproduced: no
Impact: none
Confidence: certain
Tested: 2026-09-24 13:52:26
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 13:52:26
Runtime: —
Kernel: per-fix-DF-4851
fix.diff: findings/poc/DF-4851/fix.diff
Runner: df-bsd-reviewer

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PoC verification

Evidence pack

findings/poc/DF-4851 · 1 files

File	Type	Description	Size
verdict.json	file		1.1 KB	view raw

Fix verification

not_testable

per-fix-DF-4851

Confirmed kernel references

Detail

Exploit chain

set hw.mfi.msi.enable=0 for an mfi issue -> every aac card also INTx; or NOMSI 2230S attaches before a 5405 -> 5405 gets INTx despite default=1

Evidence (decisive lines)

findings/poc/DF-4851/ (this verdict)

Verdict

Operational misconfiguration only (no memory-safety impact): aac's MSI tunable is registered under mfi(4)'s exact name (hw.mfi.msi.enable, copy-pasted from mfi_pci.c:107-108) - the natural hw.aac.msi.enable knob does not exist, boot-time settings intended for mfi silently apply to every aac adapter, and the NOMSI attach path permanently writes aac_msi_enable=0 so later MSI-capable aac cards are forced to INTx. Upstream FreeBSD uses a per-driver name. No aac hardware on the guest. Rename-the-tunable + per-device-decision fix.