# DF-1992 - Source Verification

## Verdict: REPRODUCED (source-only confirmation)

**Finding**: sys/dev/drm/radeon/rv740_dpm.c:145

**Mechanism**: do_div(tmp, reference_clock) divides by reference_clock from VBIOS with no zero-check. Zero reference_clock → #DE trap panic.

**Hardware dependency**: Requires radeon RV740 GPU with malicious VBIOS.

**Fix**: Add if(reference_clock==0) return -EINVAL before do_div.

## Verification method
Source-only confirmation. The cited code path was traced line-by-line in the
audited sys/ tree. The bug exists exactly as described. This is a HW-gated
driver finding — the vulnerable code path requires specific hardware (GPU,
controller, PHY, TPM, etc.) not present in the QEMU audit guest. Runtime
reproduction on this guest is not possible without the hardware.

## Fix validation
fix.diff authored and applied to guest source. All 40 fixes in this batch
compile cleanly in a single combined kernel build: `make -j6 nativekernel
KERNCONF=X86_64_GENERIC` → rc=0, zero -Werror violations.

**Kernel**: DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026