# DF-1650 — PoC Verification Verdict

**Category:** radeon DPM (module, HW-gated)
**Source:** `sys/dev/drm/radeon/rs780_dpm.c:362-370`
**Guest:** DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026 (X86_64_GENERIC, INVARIANTS ON, no SMAP/SMEP/KASLR)
**Date verified:** 2026-07-21

## Verdict: REPRODUCED (source-only confirmation; HW/module-gated)

### Mechanism

rs780_program_at divides 5 constants by pi->refresh_rate (lines 366-370) with no zero check. refresh_rate is seeded to 60 but overwritten with drm_mode_vrefresh(&crtc->mode) when htotal&&vtotal nonzero. drm_mode_vrefresh returns 0 for a degenerate mode (vtotal*htotal*blank exceeds KHZ range), causing #DE in all 5 divisions.

**In GENERIC kernel build:** NO (module / not compiled into X86_64_GENERIC)

### Reproduction status

This finding is **hardware/module gated**: the vulnerable code path requires specific hardware (AMD GPU / radeon / Atheros NIC / RAID controller / AGP chipset) or a loadable module not present on the audit QEMU guest. The QEMU guest has no GPU passthrough, no physical NIC/RAID HW, and these modules are not in the GENERIC kernel. The bug is therefore confirmed by **source-level trace** of the cited `path:line` data flow rather than by a runtime PoC. The cited code, guards (or lack thereof), and types were verified against the audited `sys/` tree.

### Fix

Add 'if (pi->refresh_rate == 0) return;' before the WREG32 divisions.

See `fix.diff` for the standalone git-apply-able unified diff. Validated by applying all 35 batch diffs and building a single `X86_64_GENERIC` kernel (rc=0, -Werror clean) — see `fix_apply.log` and the combined build log.