Summary

dcn10_hubp.c:1119 dst_x_offset /= param->pixel_clk_khz NO zero check. pixel_clk_khz from pipe_ctx->stream->timing.pix_clk_khz (dcn10_hw_sequencer.c:2652). dc_stream_set_cursor_position (dc_stream.c:225) only NULL-checks stream/position. dc_link.c:2146 checks upper bound only not lower. ASSERT is WARN_ON in production (os_types.h:72-77). DRM_MASTER user: mode with clock=0 then cursor move -> #DE panic. Fix: if(pixel_clk_khz==0) return.

PoC verification

Evidence pack

findings/poc/DF-1611 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-only confirmation + mechanism + fix	1.5 KB	↓ raw
fix.diff	suggested-fix	Add 'if (param->pixel_clk_khz == 0) return;' before the division.	454 B	view raw
../fix_build_combined.log	build-log	Combined 41-finding kernel build (rc=0, -Werror clean)	5.6 MB	↓ download
../fix_build_summary.txt	build-summary	Summary of the combined 41-finding kernel build	826 B	view raw

VERDICT.md verdict source-only confirmation + mechanism + fix

↓ download raw

DF-1611 — PoC Verification Verdict

Category: amdgpu DCN (module, HW-gated) Source: sys/dev/drm/amd/display/dc/dcn10/dcn10_hubp.c:1117-1119 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

hubp1_cursor_set_position divides dst_x_offset by param->pixel_clk_khz (line 1119) with no zero check. pixel_clk_khz derives from stream timing; a DRM_MASTER custom mode with pix_clk_khz=0 causes #DE panic.

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 (param->pixel_clk_khz == 0) return;' before the division.

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.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none

Evidence (decisive lines)

REPRODUCED (source-only): hubp1_cursor_set_position divides dst_x_offset by param->pixel_clk_khz with no zero check; custom mode with pix_clk_khz=0 -> #DE panic.

Verified recommended fix

REPRODUCED (source-only): hubp1_cursor_set_position divides dst_x_offset by param->pixel_clk_khz with no zero check; custom mode with pix_clk_khz=0 -> #DE panic.

Verdict