# DF-1953 Verification

## Verdict
**SOURCE-CONFIRMED, INCONCLUSIVE-RUNTIME (HW/module gated).**

The cited defect exists in the audited source at `sys/dev/drm/i915/intel_hangcheck.c:103-122`. Reproduction
on the running guest is **not possible** because the affected code path is
gated behind hardware that is not present in the audit QEMU/KVM guest
(no AMD/i915 GPU, no LSI MegaRAID, no MMC/SDHCI controller, no FireWire, no
ATAPI floppy, etc.) and/or lives in a kernel module that is not loaded on the
GENERIC-running guest.

## Mechanism (source-only confirmation)
i915 (not in GENERIC, no Intel GFX HW in guest). Source: semaphore_waits_for at L99-122 backwards-scan loop masks head with (ring->size-1) before each ioread32 at L109; post-loop *seqno=ioread32(vaddr+head+4)+1 at L122 does NOT mask (head+4). When matched MI_SEMAPHORE_MBOX at ring offset (size-4): head=size-4, head+4=size, reads 4 bytes past ring-buffer mapping.

## Recommended fix
Apply the same `& (engine->buffer->size - 1)` mask to (head+4) before ioread32.

The full `git apply`-able diff lives in `fix.diff` in this folder; it was
applied as part of a single combined 41-finding kernel build that compiled
cleanly (rc=0, -Werror clean) — see `../fix_build_summary.txt`.

## Build validation
* `git apply --check` on this fix.diff: **OK**
* Combined kernel build (`X86_64_GENERIC`, INVARIANTS ON) with all 41
  findings' fix.diffs applied: **rc=0**, no warnings, no errors.
* The patched kernel was not booted/run because the affected code path
  requires hardware that the audit guest does not have.