Summary

amdgpu_amdkfd_is_kfd_vmid L517 if((1<<vmid)&compute_vmid_bitmap) literal 1 is signed int; int<<int with shift>=32 is UB. No upper-bound check vmid (u32). On x86 shl masks count mod 32 so vmid 40/72/etc aliased to 8/15/.. falsely returns true. Downstream callers set_vm_context_page_table_base amdgpu_amdkfd_gfx_v8.c:844 WREG32(mmVM_CONTEXT8_PAGE_TABLE_BASE_ADDR+vmid-8,...) and gfx_v9.c:1031 WREG32(SOC15_REG_OFFSET(MMHUB,0,mmVM_CONTEXT0_PAGE_TABLE_BASE_ADDR_LO32)+(vmid*2),...) out-of-range VMIDs -> out-of-range MMIO offsets. LATENT: CONFIG_HSA_AMD not defined sys/dev/drm/kconfig.h:7-26 so adev->kfd always NULL is_kfd_vmid short-circuits false. Fix: vmid<32&&((1U<<vmid)&compute_vmid_bitmap).

PoC verification

Evidence pack

findings/poc/DF-1899 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	467 B	view raw
VERDICT.md	verdict	source-confirmation analysis	1.0 KB	↓ raw
build.sh	build-script	N/A (source-only)	65 B	view raw
run.sh	run-script	N/A (source-only)	89 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1899 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: amdgpu_amdkfd_is_kfd_vmid L517 if((1<<vmid)&compute_vmid_bitmap) literal 1 is signed int; int<=32 is UB. No upper-bound check vmid (u32). On x86 shl masks count mod 32 so vmid 40/72/et

Citation: sys/dev/drm/amd/amdgpu/amdgpu_amdkfd.c:514-522

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 status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.

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: UB left shift 1<<vmid with no upper-bound check (amdgpu_amdkfd.c:514-522)

Verified recommended fix

Source-confirmed: UB left shift 1<<vmid with no upper-bound check (amdgpu_amdkfd.c:514-522)

Verdict