DF-1879

Missing pipe_bpp!=0 guard in vlv_dsi_get_pclk causes kernel divide-by-zero panic

Summary

vlv_dsi_get_pclk L325 pclk=DIV_ROUND_CLOSEST(dsi_clock*lane_count,pipe_bpp) performs integer division by caller-supplied pipe_bpp with no guard. Sibling bxt_dsi_get_pclk L340-343 explicitly guards if(!pipe_bpp){DRM_ERROR(Invalid BPP(0));return 0;} confirming authors treat 0 as real possibility. VLV/CHV caller intel_dsi_get_config vlv_dsi.c:1264-1267 invokes without first setting pipe_config->pipe_bpp (GEN9_LP branch L1260-1263 calls bxt_dsi_get_pipe_config which sets it from MIPI_DSI_FUNC_PRG; else-branch does not). i9xx_get_pipe_config intel_display.c:7987-8002 only assigns pipe_bpp for 3 enumerated PIPECONF_BPC_MASK values (6/8/10BPC) silently leaves kzalloc zero for other 5 encodings of 3-bit field. Trigger: boot/resume on VLV/CHV DSI panel whose PIPECONF BPC in unhandled state (abnormal BIOS handoff/S3 resume misprogrammed PIPECONF). Root/DRM-master or physical/firmware attacker. intel_modeset_setup_hw_state at boot/resume calls get_config. Impact: hard kernel panic divide-by-zero trap. Fix: mirror bxt guard if(!pipe_bpp)return 0 before L325 division.

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Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
CWE: CWE-369
File: sys/dev/drm/i915/vlv_dsi_pll.c
Lines: 325
Area: dev
Discovered: 2026-07-20
Updated: 2026-07-20

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: panic
Confidence: likely
Tested: 2026-07-23 17:00:13
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 17:00:13
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1879/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1879 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	443 B	view raw
VERDICT.md	verdict	source-confirmation analysis	710 B	↓ raw
build.sh	build-script	N/A (source-only)	61 B	view raw
run.sh	run-script	N/A (source-only)	87 B	view raw

VERDICT.md verdict source-confirmation analysis

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DF-1879 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: vlv_dsi_get_pclk L325 pclk=DIV_ROUND_CLOSEST(dsi_clock*lane_count,pipe_bpp) performs integer division by caller-supplied pipe_bpp with no guard. Sibling bxt_dsi_get_pclk L340-343 explicitly guards if(

Citation: sys/dev/drm/i915/vlv_dsi_pll.c:325-325

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 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: missing pipe_bpp!=0 guard causes div-by-zero (vlv_dsi_pll.c:325)

Verified recommended fix

Source-confirmed: missing pipe_bpp!=0 guard causes div-by-zero (vlv_dsi_pll.c:325)

Verdict

Source-confirmed: missing pipe_bpp!=0 guard causes div-by-zero (vlv_dsi_pll.c:325)