# DF-3688 — verdict narrative

## Finding

Source-certain output-budget overflow, precondition shared with DF-1166 (VBIOS dep count > 8 is unvalidated); runtime-inconclusive on this guest (no AMD GPU). smu7_print_clock_levels sprintf()s one line per DPM level into the caller's sysfs page buffer (amdgpu_pm.c amdgpu_get_pp_dpm_sclk/mclk/pcie pass the raw 4096-byte kernfs buf; pp_od_clk_voltage likewise). The loops run to sclk_table->count / mclk_table->count / pcie_table->count / odn_*->num_of_pl - all ultimately the unvalidated VBIOS u8 count (up to 255). Measured on the guest with the exact format strings: 255 PP_PCIE lines = 4481 bytes and 255 PP_SCLK lines with u32-scale clocks = 4481 bytes, both overflowing PAGE_SIZE; the per-line reads dpm_levels[i] for i >= 8 are themselves OOB reads of the dpm_levels[8] arrays. Impact: heap overflow of the kernfs page on an UNPRIVILEGED sysfs read once the count is corrupted by a crafted VBIOS; ~385 bytes past the page.

## Root cause (kernel references)

- `sys/dev/drm/amd/powerplay/hwmgr/smu7_hwmgr.c:4428`
- `sys/dev/drm/amd/powerplay/hwmgr/smu7_hwmgr.c:4444`
- `sys/dev/drm/amd/powerplay/hwmgr/smu7_hwmgr.c:4458`
- `sys/dev/drm/amd/powerplay/hwmgr/smu7_hwmgr.c:4468`
- `sys/dev/drm/amd/amdgpu/amdgpu_pm.c:650`

## What was verified, and how

1. **Source-level certainty.** Full-file pass-2 audit of smu7_hwmgr.c (5147 lines) with
   the parse-side preconditions traced into processpptables.c / process_pptables_v1_0.c
   (VBIOS u8 counts unvalidated; offset==0 subtables parse-legal NULL) and the struct
   geometry verified in ppatomctrl.h / smu7_hwmgr.h / hardwaremanager.h /
   dm_pp_interface.h.
2. **Harness on the guest** (DragonFly 6.5-DEVELOPMENT x86_64, `cc` base toolchain):
   `sprintf_budget.c` reproduces the exact kernel code shape and/or arithmetic with 1:1 struct
   layouts. Output in `run.log`.
   Compiled with `-O0` — at `-O2` the compiler detects the array-index UB and
   misoptimizes the accounting loops (itself a hint of what the kernel code does).
3. **Hardware absence.** The guest is virtio-only: no AMD GPU on PCI, amdgpu not
   loaded. The in-kernel trigger requires an SMU7 ASIC (CI/Topaz/Tonga/Fiji/Polaris/
   Vegam) with a crafted VBIOS, VFIO passthrough of a malicious card, or a root
   sysfs pp_table write. Per pass-2 spawn instructions this is recorded as
   **inconclusive** (matching DF-3585/DF-3619/DF-3644 precedent for the same class),
   impact none *on this guest*.

## Fix validation

fix.diff authored post-verification against the read-only sys/ tree. Not built: a
kernel rebuild with drm cannot be exercised on a GPU-less guest, so fix validation is
`not_testable`; the diffs are minimal, local, and mechanically checkable against the
cited lines.

## Fix status (batch validation)
Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest `make -j6 nativekernel KERNCONF=X86_64_GENERIC` completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.