DF-1937

Divide-by-zero in spread-spectrum clock math when ATOM BIOS supplies ss.rate==0

Summary

rv730_populate_sclk_value L97-98 and rv730_populate_mclk_value L173-174 compute clk_s=reference_clock*5/(reference_divider*ss.rate) then clk_v=ss.percentage*fbdiv/(clk_s*10000) with no guard against ss.rate==0 or clk_s==0. ss.rate from GPU ATOM BIOS SS table via radeon_atombios_get_asic_ss_info: v1 usSpreadRateInKhz directly radeon_atombios.c:1546; v2/v3 usSpreadRateIn10Hz /=100 at L1569/L1594 -> if usSpreadRateIn10Hz<100 rate becomes 0 after integer divide. Divide-by-zero kernel panic on DPM-enable path radeon_dpm_enable->rv770_convert_power_level_to_smc->rv730_populate_sclk/mclk_value. DPM enabled by default radeon.dpm=1. Attacker: malicious/corrupt VBIOS Thunderbolt/PCIe/VFIO passthrough. Impact: hard kernel panic A:H no C/I. Same pattern in rv770_dpm.c:548 rv740_dpm.c:165 cypress_dpm.c:565 ni_dpm.c:2044 si_dpm.c:4831. Fix: if(ss.rate==0||clk_s==0)goto skip SS.

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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/radeon/rv730_dpm.c
Lines: 97-174
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 17:00:17
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 17:00:17
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1937/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1937 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	1.2 KB	view raw
VERDICT.md	verdict	source-confirmation analysis	709 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

↓ download raw

DF-1937 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: rv730_populate_sclk_value L97-98 and rv730_populate_mclk_value L173-174 compute clk_s=reference_clock5/(reference_dividerss.rate) then clk_v=ss.percentagefbdiv/(clk_s10000) with no guard against s

Citation: sys/dev/drm/radeon/rv730_dpm.c:97-174

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: div-by-zero when ss.rate=0 or clk_s=0 in spread-spectrum math (rv730_dpm.c:97-174)

Verified recommended fix

Source-confirmed: div-by-zero when ss.rate=0 or clk_s=0 in spread-spectrum math (rv730_dpm.c:97-174)

Verdict

Source-confirmed: div-by-zero when ss.rate=0 or clk_s=0 in spread-spectrum math (rv730_dpm.c:97-174)