DF-1876

Integer underflow in psp_v11_0_compare_sram_data loop causes OOB read of ucode buffer — variant of DF-1839

Summary

psp_v11_0_compare_sram_data L498-509 ucode_size=ucode->ucode_size (uint32_t from untrusted firmware header via amdgpu_firmware_info); while(ucode_size){ RREG32 compare *ucode_mem; ucode_mem++; ucode_size-=4; }. If ucode_size not multiple of 4 (1/2/3) subtraction underflows to ~0xFFFFFFFD/FD/FF loop continues ~1B iterations reading past ucode->kaddr OOB. No check ucode_size%4==0 anywhere. Same bug as psp_v3_1_compare_sram_data DF-1839. LATENT: only in-tree caller amdgpu_psp_check_fw_loading_status amdgpu_psp.c:547 invoked from amdgpu_psp.c:330 inside #if 0. Becomes exploitable if block re-enabled. Impact ceiling: small kernel-memory info leak + reliable local DoS via page-fault panic no write primitive. Fix: require dword alignment ucode_size%4==0 OR change loop to while(ucode_size>=4).

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Severity: Low
Status: new
Bucket: Kernel memory leaks / uninitialized disclosure
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:L/I:N/A:H
CWE: CWE-191
File: sys/dev/drm/amd/amdgpu/psp_v11_0.c
Lines: 498-509
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 17:00:12
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 17:00:12
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1876/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-1876 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	435 B	view raw
VERDICT.md	verdict	source-confirmation analysis	714 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-1876 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: psp_v11_0_compare_sram_data L498-509 ucode_size=ucode->ucode_size (uint32_t from untrusted firmware header via amdgpu_firmware_info); while(ucode_size){ RREG32 compare *ucode_mem; ucode_mem++; ucode_s

Citation: sys/dev/drm/amd/amdgpu/psp_v11_0.c:498-509

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: ucode_size-=4 underflows when not multiple of 4 (psp_v11_0.c:498-509)

Verified recommended fix

Source-confirmed: ucode_size-=4 underflows when not multiple of 4 (psp_v11_0.c:498-509)

Verdict

Source-confirmed: ucode_size-=4 underflows when not multiple of 4 (psp_v11_0.c:498-509)