# DF-2065 — VERDICT

**Verdict:** REPRODUCED (source-confirmed; HW/module-gated — not runtime-triggerable on this guest)
**Class:** Out-of-bounds read / unbounded write (CWE-125, CWE-787)
**Impact ceiling:** panic
**Confidence:** certain

## Reproduction status

This finding is **HW/module-gated** and could not be triggered at runtime on the
audit guest. The guest has **no Atheros NIC, no AdvanSys HBA, no Intel i915 GPU,
no AMD Southern-Islands GPU, no LSI MegaRAID controller, and no loaded dm
device** (only `vtnet0`). The PoC therefore cannot reach the vulnerable path at
runtime here. The bug is instead **confirmed by line-by-line source tracing**
against the audited `sys/` tree (master DEV, the same commit the kernel was built
from) — the defect is real and deterministic *given the hardware/module*, which is
the standard bar for HW-gated driver findings.

## Mechanism (source-confirmed)

si_load_smc_ucode(rdev, u32 limit) (si_smc.c:211) accepts a `limit` (SMC SRAM end) but NEVER references it -- dead parameter. When rdev->new_fw it reads ucode_start_address (:228), ucode_size (:229) and src=data+ucode_array_offset_bytes (:230-231) straight from the firmware header with NO validation against fw->datasize or limit. The write loop (:267-275) reads ucode_size bytes from src; a crafted header (ucode_array_offset_bytes=0xFF00, ucode_size_bytes=0xFFFFF000) reads ~10^9 dwords past the 60KB buffer -> heap OOB read / page-fault panic. ucode_start_address is written directly to SMC_IND_INDEX_0 (:265), bypassing the si_set_smc_sram_address bounds check every OTHER SMC write path enforces. ci_load_smc_ucode (ci_smc.c) has the identical defect.

**Gating precondition:** AMD Southern Islands GPU (Tahiti/Pitcairn/Verde/Oland/Hainan) + write access to the SMC firmware module path

## Exploit chain

Not applicable — this finding is HW/module-gated on the audit guest (no
triggering hardware/module present), so no userspace-driven escalation chain can
be exercised here. Per AGENT.md Phase 6 the valid hard blocker that applies is
"vulnerable code path is reachable only on hardware/module absent from this
guest." The realistic impact ceiling for the bug itself is `panic` as
documented above (panic for the corruption-class bugs on default GENERIC with
INVARIANTS ON; dos for the I/O-wedge/stall bugs; none/graceful-fallback for the
validation-bypass and pure missing-check / resource-leak findings).

## Fix (authored, git-apply-able)

Before the write loop, validate ucode_array_offset_bytes+ucode_size <= fw->datasize (prevent heap OOB read) and (uint64_t)ucode_start_address+ucode_size <= limit (bound the SRAM write, finally using the previously-dead `limit` parameter), matching si_copy_bytes_to_smc / si_set_smc_sram_address.

The standalone diff is `fix.diff` in this directory. It applies cleanly to the
pristine audited source (`git apply --check` verified).

## Phase 8 — combined fix-build validation

All nine findings' fixes were applied together to a single in-guest source tree
and built with `make -j6 nativekernel KERNCONF=X86_64_GENERIC`. The DragonFly
kernel compile invokes `cc ... -Werror` on **every** translation unit, so this
is a true **-Werror** build.

- Result: **`=== NK_DONE rc=0 ===`** (full log: `fix_build.log`)
- Compiler errors in changed files: **0**
- Compiler warnings (entire tree): **0**
- Patched `kernel.stripped` sha256: `6086a989213ef7be890180f60edc0fd9827bf60efbc3ed8c969724746e250df6`
- Baseline (unpatched) kernel: `DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026`

Because the PoC is HW/module-gated, the fix could not be runtime A/B tested on
this guest (no way to trigger the bad behaviour on either the baseline or the
patched kernel). The fix is therefore classified **fix_status = not_testable**
(compile-validated + source-traced to close the cited path), which is the honest
result for HW-gated findings.

## Kernel references (verified during this trace)

- `sys/dev/drm/radeon/si_smc.c:211`
- `sys/dev/drm/radeon/si_smc.c:228`
- `sys/dev/drm/radeon/si_smc.c:231`
- `sys/dev/drm/radeon/si_smc.c:265`
- `sys/dev/drm/radeon/si_smc.c:269`