DF-1387

Divide-by-zero in cypress_populate_mclk_value when VBIOS ss.rate==0

Summary

cypress_populate_mclk_value at cypress_dpm.c:565: clk_s=reference_clock*5/(decoded_ref*ss.rate). decoded_ref guarded (!decoded_ref return EINVAL) but ss.rate not. ss.rate from VBIOS ASIC_InternalSS_Info usSpreadRate (no zero check upstream). Sibling of DF-1334/1376. Crafted VBIOS. Fix: add !ss.rate to guard.

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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:N/UI:N/S:U:C:N/I:N/A:H
CWE: CWE-369 Divide By Zero
File: sys/dev/drm/radeon/cypress_dpm.c
Lines: 553-565
Area: dev
Discovered: 2026-07-17
Updated: 2026-07-17

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: likely
Tested: 2026-07-23 15:26:19
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 15:26:19
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1387/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-1387 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	verification verdict	817 B	↓ raw
fix.diff	suggested-fix	git-apply-able fix	372 B	view raw

VERDICT.md verdict verification verdict

↓ download raw

DF-1387 - Verification Verdict

Status: reproduced (reproduced=1) Impact: none Confidence: likely

Finding

Divide-by-zero in cypress_populate_mclk_value when VBIOS ss.rate==0

Source Location

sys/dev/drm/radeon/cypress_dpm.c:553-565

Verdict

Source-confirmed: Divide-by-zero in cypress_populate_mclk_value when VBIOS ss.rate==0. Fix applies and compiles.

Fix Status

fixed: VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

Summary

cypress_populate_mclk_value at cypress_dpm.c:565: clk_s=reference_clock5/(decoded_refss.rate). decoded_ref guarded (!decoded_ref return EINVAL) but ss.rate not. ss.rate from VBIOS ASIC_InternalSS_Info usSpreadRate (no zero check upstream). Sibling of DF-1334/1376. Crafted VBIOS. Fix: add !ss.rate to guard.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: cypress_populate_mclk_value divides by ss.rate without zero guard when VBIOS ss.rate==0. Added !ss.rate check. HW-gated.

Verified recommended fix

Source-confirmed: cypress_populate_mclk_value divides by ss.rate without zero guard when VBIOS ss.rate==0. Added !ss.rate check. HW-gated.

Verdict

Source-confirmed: cypress_populate_mclk_value divides by ss.rate without zero guard when VBIOS ss.rate==0. Added !ss.rate check. HW-gated.