DF-4019

debugfs amdgpu_iomem: upstream page-ownership check is #if 0'd, turning the debug file into arbitrary physical-memory read/write for debugfs holders

Summary

amdgpu_iomem_read/write translate a user-supplied bus address through the identity IOMMU map to a physical page, check only pfn_valid, then kmap + copy_to/from_user. The upstream guard restricting access to pages actually mapped by this TTM device is '#if 0 /* XXX DRAGONFLY - dev_mapping NULL atm */'. With the check gone, anyone who can open the debugfs file reads and writes ARBITRARY physical memory by llseek+read/write. Root-gated today but converts a debugging convenience into a full physmem R/W primitive. Reinstate ownership bound; 0400 until then.

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Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: certain
Pass: 2 · GLM 5.3 second pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
CWE: CWE-668
File: sys/dev/drm/amd/amdgpu/amdgpu_ttm.c
Lines: 2424-2544
Area: dev
Discovered: 2026-09-17
Updated: 2026-09-17

Team triage

untriaged

priority: — · owner: —

PoC verification

untested

Status: untested
Reproduced: no
Impact: debugfs amdgpu_iomem: the upstream page-ownership check is #if 0'd ('XXX DRAGONFLY - dev_mapping NULL atm'), so the file gives its holder arbitrary physical-memory read/write by llseek+read/write (only pfn_valid is checked).
Confidence: certain
Tested: 2026-09-17 14:39:58
Attempts: 0
Runtime: —
Code hash: —
Guest: —
Build cmd: —
Run cmd: —

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Fix verification

not_testable

Fix status: not_testable
Baseline reproduced: no
Patched reproduced: no
Confidence: certain
Tested: 2026-09-17 14:39:58
Runtime: —
Kernel: per-fix-DF-4019
fix.diff: findings/poc/DF-4019/fix.diff
Runner: df-bsd-reviewer

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PoC verification

Evidence pack

findings/poc/DF-4019 · 2 files

File	Type	Description	Size
README.md	file		222 B	↓ raw
verdict.json	file		1001 B	view raw

README.md file

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DF-4019

Low/Info finding — PoC skipped per contract (hardware-gated / dead code). Source citations in the pass-2 result block.

Fix: reinstate an ownership bound before kmap; until then create the file 0400 read-only

Fix verification

not_testable

baseline no→ patch + rebuild →patched clean

reinstate an ownership bound before kmap; until then create the file 0400 read-only

source-only

per-fix-DF-4019

Confirmed kernel references

Detail

Exploit chain

[]

Evidence (decisive lines)

source-only; path:line citations in pass-2 result block

Verdict

source-verified; root-gated via debugfs on a working amdgpu box; defense-in-depth removal vs upstream