# DF-1996 - Source Verification

## Verdict: REPRODUCED (source-only confirmation)

**Finding**: sys/dev/drm/amd/amdgpu/amdgpu_gfx.c:211

**Mechanism**: amdgpu_gfx_kiq_acquire while(queue_bit-- >= 0): when queue_bit==0, condition true, body executes with queue_bit=-1. test_bit(-1,...) → 1UL<<(-1) undefined behavior (negative shift).

**Hardware dependency**: Requires AMD GPU with KIQ (GFX compute).

**Fix**: Change >= to > in loop condition.

## 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