Summary

tpmcrb_attach trusts four values read straight from TPM CRB registers (cmd_off rsp_off cmd_buf_size rsp_buf_size) performs no validation that each buffer plus offset fits inside allocated MMIO BAR then hands them directly to unbounded bus_write_region_stream_1/bus_read_region_stream_1 in tpmcrb_transmit. Buggy/malicious TPM (software emulator behind VM hypervisor compromised platform firmware real device with register bug) can report offsets/sizes that walk off end of kernel MMIO mapping. On x86 reliably panics kernel. A second contributing defect in tpmcrb_fix_buff_offsets uses strict > when testing whether cmd_off/rsp_off fall inside ACPI memory window so buffer sitting exactly at window base (cmd_off==base_addr) left as huge absolute address used verbatim as BAR offset. Path reachable without opening /dev/tpm0 because suspend/shutdown calls tpm20_save_state->transmit.

PoC verification

Evidence pack

findings/poc/DF-2410 · 5 files

File	Type	Description	Size
VERDICT.md	verdict	analysis: code bug confirmed, gate confirmed, fix authored	1.6 KB	↓ raw
fix.diff	suggested-fix	git-apply-able defense-in-depth fix (verified --check clean)	1.0 KB	view raw
env.txt	environment	guest gate-proof: usbconfig/pciconf/ifconfig/devinfo/sysctl output	2.0 KB	view raw
build.sh	build-script	no-op (no live-device PoC)	255 B	view raw
run.sh	run-script	gate check (required device is absent)	333 B	view raw

VERDICT.md verdict analysis: code bug confirmed, gate confirmed, fix authored

↓ download raw

DF-2410 — PoC verdict

File: sys/dev/crypto/tpm/tpm_crb.c

Verdict: NOT REPRODUCED on this QEMU guest — confirmed HW/ACPI/device-gated; the code bug is REAL and a defense-in-depth fix.diff is attached.

Mechanism (confirmed in source)

tpmcrb_attach trusts four values read straight from TPM CRB registers (cmd_off, rsp_off, cmd_buf_size, rsp_buf_size) and never validates that each buffer+offset fits inside the allocated MMIO BAR; they are then used as BAR offsets in unbounded bus_write_region_stream_1/bus_read_region_stream_1 in tpmcrb_transmit.

Cited lines

Why it does not reproduce on this guest

No TPM (CRB or otherwise) on the QEMU guest (no /dev/tpm*; tpm_crb does not attach; the guest is booted without a TPM backend).

Guest gate-proof (full usbconfig/pciconf/ifconfig/devinfo/sysctl/kldstat output) is in env.txt.

Defense-in-depth fix

After reading the four register values, validate cmd_off+cmd_buf_size and rsp_off+rsp_buf_size each fit within rman_get_size(sc->mem_res); otherwise release the BAR and return ENXIO.

The git-apply-able diff is in fix.diff (verified git apply --check clean).

Classification

status: not_reproduced
reproduced: 0
impact: none (not reachable on this guest; latent code bug confirmed in source)
confidence: certain (code bug + gate both confirmed by direct source trace and guest enumeration)
fix_status: not_testable (patch applies + compiles-correct by inspection, but no live device to exercise on this guest)

Fix verification

not_testable

baseline no→ patch + rebuild →patched clean

not_testable: target device absent on this guest. fix.diff applies clean and is source-correct; no live device to exercise.

git apply --check findings/poc/DF-2410/fix.diff -> OK. No runtime test possible (HW/ACPI/device-gated).

↓ fix.diffper-fix-DF-2410

Detail

Exploit chain

none — valid hard blocker (driver/device path dead at runtime on this guest: no target HW/ACPI/device). No unprivileged->root path.

Evidence (decisive lines)

usbconfig list -> No device match; pciconf -l -> no target HW/capability; ifconfig -> vtnet0 lo0; kldstat -> kernel/ehci/xhci only; sysctl/devinfo -> no target OIDs. Source confirmed at cited lines.

PoC changes

Created findings/poc/DF-2410/{VERDICT.md,fix.diff,manifest.json,env.txt,build.sh,run.sh}. No PoC source (HW/ACPI/device-gated).

Verified recommended fix

Defense-in-depth fix.diff closes the cited path (see findings/poc/DF-2410/fix.diff; git apply --check OK).

Verdict

NOT REPRODUCED (HW/ACPI/device-gated on this guest). The bug is REAL in source (traced line-by-line): tpm_crb TPM-reported CRB buffer offsets used as BAR (no TPM, no /dev/tpm). Gate confirmed via usbconfig list (no devices), pciconf -l (no target HW/capability), ifconfig (vtnet0 lo0 only), kldstat (no target module), sysctl/devinfo (no target ACPI/device OIDs). The benign QEMU environment cannot produce the malicious device/ACPI/descriptor the bug requires.

TPM-reported CRB buffer offsets/sizes used as BAR offsets without any BAR bounds check (and off-by-one in offset normalization)