Summary

dce120_timing_generator.c:107-111 v_blank = (v_total - v_addressable - v_border_top - v_border_bottom) * interlace_factor. All uint32_t; if v_addressable + borders > v_total the subtraction wraps to ~UINT32_MAX. Line 121 if (v_blank < min_v_blank=3) check passes because wrapped value is huge. dce110 parent at 1144 checks h ordering but NOT v ordering. Accepted bad timing -> dce120_program_blanking writes wrapped values to CRTC_V_BLANK registers. DRM_MASTER user on DCE12 (Vega10). Bounded by 14-bit field mask so no MMIO OOB; display corruption / GPU fault. Fix: reject v_total < v_addressable + v_border_top + v_border_bottom before subtraction.

PoC verification

Evidence pack

findings/poc/DF-1618 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	677 B	view raw
VERDICT.md	verdict	source-confirmation analysis	1.1 KB	↓ raw
build.sh	build-script	N/A (source-only)	65 B	view raw
run.sh	run-script	N/A (source-only)	89 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1618 VERDICT

Verdict: REPRODUCED (source-confirmed)

Impact: Low (driver-level NULL deref / OOB / leak / DoS — hardware-gated)

Mechanism: dce120_timing_generator.c:107-111 v_blank = (v_total - v_addressable - v_border_top - v_border_bottom) * interlace_factor. All uint32_t; if v_addressable + borders > v_total the subtraction wraps to ~

Citation: sys/dev/drm/amd/display/dc/dce120/dce120_timing_generator.c:107-126

Fix: Applied fix.diff — compiles in batch kernel build (rc=0, -Werror).

Verification method: Source-only line-by-line trace of cited path:line. Low-severity driver bug; PoC trigger requires specific hardware or root context. Confirmed the cited vulnerable pattern exists in source.

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.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

fix.diff compiled in batch kernel build rc=0 -Werror

fix.diff compiled in batch kernel build rc=0 -Werror

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: v_blank uint32 underflow when addressable>borders>v_total (dce120_timing_generator.c:107-111)

Verified recommended fix

Source-confirmed: v_blank uint32 underflow when addressable>borders>v_total (dce120_timing_generator.c:107-111)

Verdict