Guide for PCIe DMA threat modeling, FPGA-based memory access, and defensive implications in game security. Use this skill when researching pcileech, BAR and TLP behavior, page-table walking, IOMMU or VT-d, device impersonation, firmware mimicry, or DMA detection and mitigation in game security research.
Guide for PCIe DMA threat modeling, FPGA-based memory access, and defensive implications in game security. Use this skill when researching pcileech, BAR and TLP behavior, page-table walking, IOMMU or VT-d, device impersonation, firmware mimicry, or DMA detection and mitigation in game security research.
DMA Attack Techniques
Overview
This skill covers Direct Memory Access research from the awesome-game-security collection, focusing on FPGA-based PCIe attacks, pcileech usage, physical-memory access workflows, and the defensive limits of software anti-cheat once a hostile device can read memory below the OS.
README Coverage
Cheat > DMA
Anti Cheat > Detection:DMA
Anti Cheat > Detection: Hacked Hypervisor
Anti Cheat > Detection:Virtual Environments
Anti Cheat > Detection:HWID
Windows Security Features
Threat Model
External DMA Cheat Architecture
A modern external DMA cheat consists of three components:
1. Cheat PC — runs the cheat application, signature databases,
aim assistance, ESP rendering, and a network/USB link to the gaming PC.
2. DMA Card — an FPGA-based PCIe endpoint installed in the gaming PC
(typically M.2 NVMe slot). Exposes a memory-read/write interface to
the cheat PC. Uses Bus Master capability to issue Memory Read TLPs
against the gaming PC's RAM.
3. Actuator (optional) — a USB HID emulator (microcontroller-based) that
injects keyboard/mouse input on the gaming PC according to commands
from the cheat PC, closing the loop.
The structural property that makes this threat distinctive:
no attacker code executes on the gaming PC. The DMA card performs
hardware-level transactions between the FPGA and the gaming PC's
memory controller, mediated by the chipset and (when configured) the IOMMU.
The gaming PC's OS, drivers, and anti-cheat see only a PCIe device
announcing itself through Configuration Space and performing what looks
like ordinary DMA.
Three Defense Layers
Layer Mechanism What It Catches
─────────────────────────────────────────────────────────────────────────────
PCIe-layer Inspect Config Space & Identity mismatch — spoofed
fingerprinting behavior at the bus level device that doesn't match
real silicon's full signature
IOMMU Use the IOMMU to bound Out-of-domain DMA — device
enforcement what physical memory the trying to read game memory
device can touch it wasn't allocated
External TPM-anchored measured boot, Boot-chain compromise — IOMMU
attestation cloud-verified or kernel itself subverted
PCIe Protocol Stack
Three Protocol Layers
Layer Unit Function
────────────────────────────────────────────────────────────────
Transaction TLP Memory/IO/Config reads & writes,
completions, messages
Data Link DLLP Acknowledgements, flow control
credits, power management
Physical Ordered Sets Link training, equalization,
clock recovery
A real device's behavior is shaped by all three layers.
Many FPGA designs primarily customize Transaction-Layer behavior; Physical and
Data Link behavior may retain implementation fingerprints unless the selected
IP, configuration, and surrounding behavior closely match the claimed device.
Whether a fingerprint is usable must be validated on the actual link.
TLP (Transaction Layer Packet) Format
Every TLP contains a 3 DW (12-byte) or 4 DW (16-byte) base header; optional
TLP Prefixes may precede it. 4 DW headers are used for 64-bit addresses and
certain message types.
First DWord (DW0) encoding:
Bits Field Notes
[31:29] Fmt[2:0] Header format + data presence
[28:24] Type[4:0] TLP type (combined with Fmt)
[22:20] TC[2:0] Traffic Class (default 0)
[18] Attr[2] ID-Based Ordering (IDO)
[15] TD TLP Digest (ECRC trailer)
[14] EP Poisoned data
[13:12] Attr[1:0] Relaxed Ordering, No Snoop
[11:10] AT[1:0] Address Type (critical for ATS bypass)
[9:0] Length[9:0] Payload length in DWords (0x000 = 1024 DW = 4 KB)
Fmt[2:0] encoding:
000 = 3 DW header, no data
001 = 4 DW header, no data
010 = 3 DW header, with data
011 = 4 DW header, with data
100 = TLP Prefix
Key TLP types (Fmt + Type combinations):
Fmt Type TLP
000 0_0000 MRd (Memory Read, 3DW / 32-bit addr)
001 0_0000 MRd (Memory Read, 4DW / 64-bit addr)
010 0_0000 MWr (Memory Write, 3DW)
011 0_0000 MWr (Memory Write, 4DW)
000 0_0100 CfgRd0 (Config read — terminate at this device)
010 0_0100 CfgWr0
000 0_0101 CfgRd1 (Config read — forwarded by bridges)
010 0_0101 CfgWr1
000 0_1010 Cpl (Completion without data)
010 0_1010 CplD (Completion with data)
001 1_0rrr Msg (Message, no data)
011 1_0rrr MsgD (Message with data)
Detection-Relevant DW0 Fields
TC[2:0] — Traffic Class. Default traffic commonly uses TC0, but non-zero TC is
valid when platform and device policy configure it. Compare usage with the
claimed device, driver, and workload rather than flagging it in isolation.
Attr[2:0] — RO/NS/IDO. A device emulating a NIC must follow that NIC's
typical NS/RO usage pattern; mismatches are visible.
AT[1:0] — Address Type:
00 = Untranslated (IOMMU will translate)
01 = Translation Request (ATS only)
10 = Translated (device claims it has already translated via ATS)
This field is the basis of ATS bypass attacks.
TD — TLP Digest. If set, an ECRC trailer is present.
EP — Poisoned. Indicates data is known-bad.
TLP Routing and Requester ID
Three routing modes:
- Address routing — Memory and IO TLPs, matched against bridge apertures
- ID routing — Config TLPs and Completions, by BDF
- Implicit routing — Some Messages (broadcast, terminate at root)
DW1 carries the Requester ID (16 bits = Bus:Device:Function, "BDF")
and an 8-bit Tag for matching completions to requests.
Requester ID is a key input to IOMMU lookup, ACS source validation, AER source
identification, and interrupt-remapping policy. If spoofed IDs are accepted
without topology or source validation, per-function isolation can be
undermined; the exact effect depends on the platform and remapping path.
Transaction categories:
- Posted (P) — fire-and-forget (Memory Writes, Messages)
- Non-Posted (NP) — requires completion (Memory Reads, IO/Config R/W)
- Completion (Cpl/CplD) — response to Non-Posted requests
Completion Status codes:
000 = Successful Completion (SC)
001 = Unsupported Request (UR)
010 = Configuration Request Retry Status (CRS)
100 = Completer Abort (CA)
UR vs CA distinction matters for spoofing detection — real silicon
responds differently to malformed config accesses vs accesses to
unimplemented offsets. Many spoofed firmwares hard-code one or the other.
Memory Read Completion Splitting
A single Memory Read TLP returns up to Max_Read_Request_Size (MRRS) bytes.
The completer splits the payload at any boundary >= RCB
(Read Completion Boundary, 64 or 128 bytes).
Each fragment cannot exceed Max_Payload_Size (MPS).
Each Completion carries:
- Lower Address[6:0] — lowest 7 bits of first byte address
- Byte Count[11:0] — bytes remaining (last fragment's Byte Count
equals its own payload length)
- BCM — PCI-X compatibility (typically 0)
- Tag — matches originating MRd's Tag
The split pattern (fragment count, boundary positions) is a
strong fingerprint: real memory controllers produce characteristic
distributions of fragment sizes and inter-fragment gaps.
BRAM-backed emulators producing perfectly uniform 64-byte fragments
at constant cadence are anomalous.
Tag Space and Fingerprinting
- 5-bit Tag (original): 32 outstanding non-posted requests per Requester ID
- Extended Tag (PCIe 1.1+, Device Control[8]): 8-bit / 256 outstanding
- 10-Bit Tag (PCIe 4.0+, Device Control 2[12]): 1024 outstanding
Tag turnover discipline — which tags get reissued and how quickly —
reflects the device's internal request tracking pipeline.
Firmware that issues reads with no tag turnover (same tag, or monotonic
beyond negotiated limit) is observably distinct from real silicon.
MPS and MRRS as Fingerprints
Both are negotiated once at link bring-up and fixed for the session.
- Device Capabilities[2:0]: Max_Payload_Size_Supported
(0=128, 1=256, 2=512, 3=1024, 4=2048, 5=4096 bytes)
- Device Control[7:5]: current MPS (must be <= Supported,
set to minimum of all devices in hierarchy)
- Device Control[14:12]: Max_Read_Request_Size (same encoding)
The discriminator is donor consistency: a device claiming a donor
that is known to support larger payloads, different tag behavior,
or a different negotiated profile should match that donor under
the same root-port constraints.
Data Link Layer
DLLPs provide reliable delivery between Physical and Transaction layers.
DLLP Purpose
─────────────────────────────────────────
Ack TLP received correctly
Nak TLP received with error; sender must replay
InitFC1/2 Flow control credit initialization at link bring-up
UpdateFC Ongoing flow control credit updates
PM_* Power management (L0s, L1 entry/exit)
Vendor Vendor-defined
Flow control credits are per TLP category:
- PH / PD — Posted Header / Data
- NPH / NPD — Non-Posted Header / Data
- CplH / CplD — Completion Header / Data
Negotiated credit values are not generally exposed through standard
Link Capabilities register. They are visible in protocol-level traces,
some root-port/vendor performance counters, or FPGA-side debug.
Useful for lab fingerprinting and forensic captures, not normal
runtime config-space detection.
Physical Layer
Two details matter even without PHY-level instrumentation:
LTSSM (Link Training and Status State Machine):
- States: Detect → Polling → Configuration → L0 (operational)
→ L0s, L1, L2 (low-power) → Recovery → Hot Reset → Disabled → Loopback
- Observable via Link Status Register and root-port performance counters
Detection-relevant:
- Negotiated Link Width (Link Status[9:4]):
Compare with slot wiring, platform policy, signal quality, and matched donor
deployments; devices can legitimately train below maximum width
- Current Link Speed (Link Status[3:0]):
A lower negotiated generation is contextual, not a contradiction by itself
- Recovery cycle frequency:
Comparative signal; materially different from donor reference is anomalous
ASPM (Active State Power Management):
- L0s and L1 are link-level low-power states
- Capability does not imply the platform enabled ASPM; evaluate transitions only
under verified policy and workload conditions that should exercise them
Configuration Access Mechanisms
Two mechanisms on x86:
CAM (Legacy I/O-port path):
1. CPU writes to I/O port 0xCF8 (Bus:Device:Function:Register)
2. CPU reads/writes at I/O port 0xCFC
- Reaches only first 256 bytes
- Still used during early BIOS/UEFI boot
ECAM (Enhanced, MMIO path):
1. Read MCFG ACPI table for segment base addresses
2. Compute: addr = base + ((bus << 20) | (dev << 15) | (func << 12) | offset)
3. OS maps physical address into kernel virtual memory
- Required for Extended Configuration Space (0x100–0xFFF)
- Where AER, DSN, LTR, VSEC, ATS, PASID, SR-IOV live
On Windows, supported paths are:
- IRP_MN_READ_CONFIG / IRP_MN_WRITE_CONFIG
- BUS_INTERFACE_STANDARD.GetBusData / SetBusData
Production anti-cheat should use documented bus interfaces;
direct MCFG mapping is a lab-only technique.
PCIe Configuration Space
Legacy 256-Byte Header (Type 0 Endpoint)
Offset Field Notes
0x00 Vendor ID (2B) Chip manufacturer (e.g., 0x8086 Intel)
0x02 Device ID (2B) Specific product
0x04 Command (2B) BME (bit 2), MemSpace (bit 1), IOSpace (bit 0)
0x06 Status (2B) Capabilities List (bit 4)
0x08 Revision ID + Class Code Class triplet: Base / Sub / ProgIF
0x0C Cache Line / Latency / Header Type 0x00 = endpoint,
Header Type / BIST 0x01 = bridge, 0x80 = multi-function
0x10–27 BAR0–BAR5 Memory or I/O windows
0x2C Subsystem Vendor ID Often distinguishes board manufacturers
0x2E Subsystem Device ID
0x30–33 Expansion ROM Base
0x34 Capabilities Pointer Offset of first capability in linked list
0x3C IRQ Line/Pin/Min/Max Legacy INTx routing
BAR encoding (32-bit BAR):
bit 0: 0 = Memory BAR, 1 = I/O BAR
bits 2:1: 00 = 32-bit, 10 = 64-bit (BAR pair)
bit 3: Prefetchable
BAR size discovery: write 0xFFFFFFFF to BAR, read back.
Lower bits (except type bits) come back as 0; rest form a size mask.
Real silicon's size masks are device-specific; a spoofed BAR with
64 KB mask when the donor uses 4 KB is detectable in one operation.
Capabilities Chain
If Status[4] is set, 0x34 points to the first capability.
Each capability has a 2-byte header: [ID | Next].
Next is DWord-aligned in 0x40–0xFF, or 0x00 to terminate.
Common capability IDs:
ID Capability
0x01 PCI Power Management
0x05 MSI
0x10 PCI Express
0x11 MSI-X
0x12 SATA Configuration
0x13 PCI Advanced Features
0x14 Enhanced Allocation
Detection: walk the chain, validate each capability's declared size
doesn't overlap the next, Next is DWord-aligned and within bounds,
no cycle exists. A malformed chain is itself a signal.
PCIe Express Capability (ID 0x10)
The single most important capability for spoofing detection.
Offset Field Notes
+0x02 PCIe Capabilities Cap Version, Device/Port Type, Slot Impl
+0x04 Device Capabilities MPS Supported, FLR, Phantom Functions
+0x08 Device Control MPS current, MRRS, Error Enables
+0x0A Device Status CED, NFED, FED, URD, Transactions Pending
+0x0C Link Capabilities Max Link Speed/Width, ASPM, L0s/L1 latencies
+0x10 Link Control ASPM Control, RCB, Link Disable, Retrain
+0x12 Link Status Current Link Speed/Width, Link Training
+0x24 Device Capabilities 2 Completion Timeout Ranges, AtomicOp,
OBFF, LTR mechanism
+0x28 Device Control 2 Completion Timeout Value, AtomicOp, LTR Enable
+0x2C Link Capabilities 2 Supported Link Speeds Vector
+0x30 Link Control 2 Target Link Speed, Compliance
+0x32 Link Status 2 De-emphasis, EQ Phase status
Detection leverage per field:
- Device Type (+0x02[7:4]): must match donor's role
- MPS Supported (+0x04[2:0]): hard-IP ceiling contradicts donor
- FLR support (+0x04[28]): verify FLR changes same sticky/non-sticky
state as claimed donor; naive firmware acknowledges FLR but continues
unchanged, producing state inconsistent with donor-defined reset semantics
- Link Status (+0x12): Width/Speed are negotiated, observable, hard to
lie about — hard IP reports what LTSSM actually achieved
- Slot Clock Config (+0x12[12]): must match real platform behavior
- Completion Timeout ranges (+0x24): selecting outside claimed ranges
is a discriminator
- AtomicOp (+0x24[6-9]): server-class GPUs/NICs may support; FPGA
support depends on IP generation and configuration; compare advertised and
exercised behavior with the claimed donor
MSI and MSI-X Capabilities
MSI (ID 0x05):
Message Control bits:
[0] MSI Enable
[3:1] Multiple Message Capable (0–5, representing 1–32 vectors)
[6:4] Multiple Message Enable (cannot exceed Capable)
[7] 64-bit Address Capable
[8] Per-Vector Masking Capable
x86 MSI Address: bits [31:20] fixed at 0xFEE (LAPIC prefix)
[19:12] Destination ID, [3] Redirection Hint, [2] Destination Mode
Message Data: [15] Trigger Mode, [10:8] Delivery Mode, [7:0] Vector
MSI-X (ID 0x11):
- Supports up to 2,048 vectors
- Table stored in BAR-mapped region (not Config Space)
- Each entry: 16 bytes (Addr Low, Addr High, Data, Vector Control)
- PBA (Pending Bit Array): bit-per-vector pending state
Naive MSI-X emulation failures:
- Ignores Vector Control Mask writes
- Sets PBA bits but never clears on unmask
- Returns hardcoded PBA values
- Doesn't retire pending interrupts when masks clear
Detection probe: mask vector → induce interrupt condition →
observe PBA bit → unmask → observe interrupt firing.
A conforming implementation should satisfy the relevant MSI-X semantics;
incomplete emulations may fail, while sophisticated emulations can pass.
AER Extended Capability (ID 0x0001)
Three error classes:
- Correctable: Receiver Error, Bad TLP, Bad DLLP, Replay Timer Timeout
- Uncorrectable Non-Fatal: Completion Timeout, Completer Abort, UR, ACS Violation
- Uncorrectable Fatal: Malformed TLP, DLL Protocol Error, Surprise Down
Each has Status (sticky, W1C), Mask, and Severity registers.
Header Log (16B) captures full TLP header of first logged uncorrectable error.
Detection:
- Absence of AER when donor model is known to expose it = mismatch
- Zero correctable-error count over long window when donor's silicon
normally produces a baseline rate = anomalous
- Anomalous UR response patterns to probes of unimplemented offsets
Extended Capabilities
4-byte header at each offset:
[31:20] Next Capability Offset (0 to terminate)
[19:16] Capability Version
[15:0] Extended Capability ID
Key Extended Capability IDs:
0x0001 AER
0x0002 Virtual Channel (VC)
0x0003 DSN (Device Serial Number, 8 bytes)
0x000B Vendor-Specific Extended Capability (VSEC)
0x000D ACS (Access Control Services)
0x000E ARI
0x000F ATS (Address Translation Services)
0x0010 SR-IOV
0x0015 Resizable BAR (RBAR)
0x0018 LTR (Latency Tolerance Reporting)
0x001B PASID
0x001D DPC (Downstream Port Containment)
0x001E L1 PM Substates
0x001F Precision Time Measurement (PTM)
Detection-relevant:
- DSN: 8-byte unique serial; donor-cloned firmware can collide
with another player's identical card
- VSEC: Xilinx PCIe IP optionally emits VSEC blocks with
characteristic Vendor ID + VSEC ID combinations
- ATS/PASID/SR-IOV presence on consumer-class donor is
demographically suspicious — rare outside server-class hardware
IOMMU Architecture
Translation Flow
1. Device issues Memory TLP with target IOVA.
TLP header carries 16-bit Requester ID (BDF).
2. TLP travels upstream through switches/bridges to root complex.
3. IOMMU intercepts, uses Requester ID to look up translation context.
4. IOMMU walks device's I/O page tables: IOVA → physical address.
5. Permission bits (Read, Write) checked against access type.
6. Success: TLP forwarded with translated physical address.
7. Failure: fault logged, device receives UR or CA completion.
Translations cached in IOTLB (I/O Translation Lookaside Buffer).
When mappings change, IOTLB must be invalidated.
Two distinct caches when ATS is in use:
- IOMMU's own IOTLB
- Device-side TLB (DevTLB) caching prior translations
Full invalidation with ATS requires:
1. IOMMU invalidates own IOTLB
2. IOMMU sends ATS Invalidate Request Message to device
3. Device drops affected DevTLB entries, replies with Invalidate Completion
If step 2 or 3 is skipped, device retains stale translations
and can DMA to unmapped addresses.
VT-d invalidation granularities:
- Global: flush entire IOTLB
- Domain-Selective: flush all entries for a Domain ID
- Page-Selective: flush specific IOVA range in a domain
Strict vs lazy invalidation:
Lazy mode defers IOTLB invalidation, batching them for performance.
Opens a window where stale translations remain valid — a device
whose driver has unmapped a buffer can still DMA to the old IOVA.
Fault Recording
VT-d: Fault Recording Registers — circular array capturing
Requester ID, faulting IOVA, fault reason, TLP type.
AMD-Vi: Event Log Buffer — producer-consumer ring buffer of
IO_PAGE_FAULT, INVALID_DEVICE_REQUEST, ATS-related events.
Both surface faults via interrupts and event-log entries.
On Windows, some IOMMU violations observable through WHEA/bug-check
paths and Driver Verifier DMA-violation telemetry.
Per-device fault rate is one of the most operationally useful
IOMMU-layer signals, but its baseline is platform-, device-, driver-, firmware-,
and workload-specific. Sustained faults show failed or invalid DMA requests;
driver bugs, resets, stale mappings, or hardware faults must be excluded before
attributing malicious out-of-domain access.
RMRR/IVMD:
ACPI DMAR table contains RMRR (Reserved Memory Region Reporting)
sub-tables declaring physical ranges devices need identity-mapped.
AMD-Vi has analogous IVMD (I/O Virtualization Memory Definition)
in the IVRS table. A defender should enumerate these and reject
configurations where suspect BDFs appear in RMRR scope or
RMRR ranges overlap game memory regions.
IOMMU Topology and Isolation
IOMMU Groups
Devices in the same IOMMU group may not be safely isolated from
one another. Group membership determined by:
- PCIe topology — devices behind a switch share a group
unless the switch supports and enables ACS
- ACS state of upstream bridges
- Quirks for known-broken hardware
Linux: /sys/kernel/iommu_groups/N/devices/
Windows: equivalent constraints but no simple public group filesystem
ACS (Access Control Services, Extended Cap ID 0x000D)
ACS is a PCIe capability that switches/root ports advertise
to declare they can enforce isolation between downstream ports.
ACS Capability register enable bits:
Bit Feature Effect
0 Source Validation (SV) Drop TLPs with wrong Requester ID
1 Translation Blocking (TB) Block AT=10 (Translated) TLPs
2 P2P Request Redirect (RR) Force P2P requests upstream for IOMMU
3 P2P Completion Redirect (CR) Force P2P completions upstream
4 Upstream Forwarding (UF) Forward upstream regardless
5 P2P Egress Control (EC) Allow/deny P2P routing per-port
6 Direct Translated P2P (DT) Allow P2P with translated addresses
Critical for untrusted endpoints: SV, TB, RR, and CR.
A switch missing Source Validation lets a malicious device spoof
its Requester ID, defeating per-BDF IOMMU translation.
A switch missing P2P Request Redirect allows devices on the same
switch to DMA directly to each other without IOMMU involvement.
Peer-to-Peer DMA
Devices on the same PCIe tree can send Memory TLPs directly to
each other's BAR ranges without involving system memory.
Without ACS redirection, peer traffic may remain below the root complex and
bypass the host IOMMU translation path. Routing behavior is topology- and
platform-specific, so confirm it with the actual root complex and switches.
Plausible P2P DMA targets for cheat:
- GPU framebuffer — rendered game state
- Network adapter ring buffers — game traffic
- USB controller queues — input device data
Mitigation: ACS Translation Blocking + P2P Request Redirect
on every intermediate bridge. Defender must walk topology and
confirm both bits are active.
Interrupt Remapping
MSI/MSI-X interrupts are Memory Writes to 0xFEE00000–0xFEEFFFFF.
Without Interrupt Remapping (IR), any device with Bus Master enabled
can write to this range and trigger arbitrary interrupts — NMIs, SMIs,
or vectors targeting wrong CPU.
With IR enabled, IOMMU validates MSI/MSI-X writes and uses
remapping-table state to determine permitted destination.
IR is part of VT-d's broader DMA Remapping architecture.
Both VT-d and AMD-Vi have integrated equivalents.
Both should be mandatory in any anti-cheat threat model.
ATS, PASID, and Address Translation Trust
ATS (Address Translation Services, Extended Cap ID 0x000F)
ATS lets a device cache IOMMU translations locally:
1. Device issues Translation Request TLP (AT=01) with IOVA
2. IOMMU translates and responds with Translation Completion
carrying physical address
3. Device caches translation in Device-side TLB (DevTLB)
4. Subsequent accesses issued with AT=10 (Translated) —
IOMMU bypasses page-walk, trusting device's cached translation
5. On mapping changes, IOMMU sends Invalidation Request
Attack surface: malicious device claiming ATS can present
arbitrary AT=10 TLPs whose addresses were never approved
by the IOMMU. The IOMMU forwards them trusting the device's claim.
PASID (Extended Cap ID 0x001B)
Extends ATS to per-process address spaces. 20-bit PASID carried
in a TLP Prefix. IOMMU uses (Requester ID, PASID) jointly
to select translation context.
PASID enables Shared Virtual Memory (SVM) — primarily found in
datacenter NICs, AI accelerators. Presence on a consumer card
is anomalous.
ATS Trust Model and "ATS Untrusted" Mode
The fundamental trust assumption: device honestly reports
translations it has been granted. Unreasonable for external
Thunderbolt enclosures, FPGAs in M.2 slots, or untrusted
accelerator cards.
Modern OS/IOMMU stacks can treat endpoints as ATS-untrusted:
ATS is disabled, blocked by policy, or stripped.
Linux: pci=noats plus per-device quirks.
Windows: Kernel DMA Protection / DMAGuard matters, but don't
treat "Kernel DMA Protection: On" as proof every internal
endpoint is ATS-untrusted. Verify ATS state per endpoint.
Driver–IOMMU Contract and Bypass Catalog
Legitimate DMA Path (Windows)
1. Acquire DMA adapter: IoGetDmaAdapter / WDF wrapper
2. Allocate buffer: MmAllocateContiguousMemorySpecifyCacheNode
or WdfCommonBufferCreate
3. Map for DMA: AllocateCommonBuffer / MapTransferEx
- OS allocates IOVA from device's domain
- Creates IOMMU page-table entries: [IOVA, IOVA+size) → physical pages
- Returns IOVA to driver
4. Program device: driver writes IOVA into device's BAR registers
5. Device DMAs: TLPs arrive at IOMMU with BDF + IOVA
6. IOMMU translates: page-walk produces physical address
7. Completion and unmap: teardown IOMMU entries + IOTLB invalidation
In this model, device can DMA only to addresses the driver
explicitly mapped. Game memory is not in that range.
Six Paths to Out-of-Domain Access
1. IOMMU not active or not applied to this path
VT-d/AMD-Vi disabled, OS not enforcing, device outside protected ports
2. Pre-boot DMA injection
Inject before IOMMU initialized; requires firmware-level exploit
3. Identity-mapped / passthrough domains
Legacy drivers request 1:1 mapping; modern strict-mode rejects it
4. Driver mapping over-allocation (Thunderclap class)
OS maps full 4 KB page when buffer is smaller; adjacent kernel data exposed
5. Legitimate-path data exfiltration
Cheat spoofed as NIC; OS network stack passes game packets through
NIC's RX ring buffer (legitimately IOMMU-mapped). Cheat reads game data
without leaving allowed mappings. Undetectable at IOMMU layer.
6. IOMMU page-table manipulation via kernel compromise
BYOVD / vulnerable driver reprograms IOMMU tables.
Requires code execution on gaming PC.
Approaches 1–3 are the foundation of most current DMA cheats.
IOMMU Bypass Catalog (16 Techniques)
# Technique Mechanism Mitigation
─────────────────────────────────────────────────────────────────────────────────
1 IOMMU disabled VT-d/AMD-Vi off in BIOS Refuse misconfigured platforms
2 Pre-boot DMA Firmware leaves injection window UEFI updates; verify ACPI indicators
3 Identity/passthrough 1:1 IOVA-to-physical mapping Strict-mode IOMMU policy
4 Driver over-allocation Full 4 KB page, adjacent data OS bounce buffers; strict mappings
5 ATS abuse AT=10 TLPs with arbitrary addrs ATS Untrusted mode for non-allowlisted
6 ACS missing on bridge P2P or spoofed Requester ID Verify ACS state on all bridges
7 Lazy IOTLB invalidation Stale translations valid briefly Strict invalidation mode
8 FLR race FLR/Hot Reset race window Synchronized FLR handling
9 SMM bypass SMM code exempt from IOMMU Boot Guard / Platform Secure Boot
10 DMA-remapping driver bugs Bugs in OS IOMMU manager OS patching
11 Hypervisor escape Compromised hypervisor VBS / measured boot; TPM attestation
12 Interrupt injection (no IR) Write arbitrary interrupts Mandatory IR enforcement
13 RMRR/IVMD scope abuse Fake ACPI tables cover attacker Measured boot; runtime RMRR audit
physical ranges
14 Snoop-bit manipulation Stale cache lines visible Strict snoop enforcement
15 PASID confusion Misconfigured PASID Table PASID-aware IOMMU programming
16 DMAR/IVRS spoofing Compromised firmware, fake tables Measured boot covering firmware
Techniques 1–6: active attack surface for current commercial DMA cheats
Techniques 7–13: academic, APT, firmware-level contexts
Techniques 14–16: largely theoretical
FPGA Hardware
Xilinx PCIe Integrated Block
Hardened IP block handling:
- Physical Layer (PHY, 8b/10b or 128b/130b, LTSSM, equalization)
- Data Link Layer (sequence numbers, replay buffer, flow control)
- Transaction Layer framing and parsing
- Subset of Configuration Space
IP core documentation:
- PG054 for 7-series
- PG156 for UltraScale Gen3
- PG213 for UltraScale+ Gen4
User logic interfaces over AXI-Stream (TX/RX) and separate
config management: cfg_mgmt_* (7-series), cfg_ext_* (UltraScale).
Detection consequences:
- Default fingerprints leak through: hard block populates Config Space
with Xilinx-characteristic byte patterns
- 7-series firmware authors who don't understand cfg_mgmt_* leave
subtle behavioral differences (some CfgTLPs return hard-block defaults)
BRAM size caps:
shadow config + writable overlay + BAR emulation + state machines.
T35 (1.8 Mbit) struggles with full 4 KB shadow + 64 KB BAR + jitter buffers.
T100 (4.86 Mbit) fits comfortably.
Zynq ZU3 (7+ Mbit) has effectively unlimited room.
LUT count caps behavioral complexity:
Each subsystem (MSI generator, ASPM FSM, AER counter, BAR responder)
costs thousands of LUTs. T35 holds 1–2; T100 the full set;
Kintex/Zynq adds runtime-reconfigurable parameter tables.
PHY transceiver family (GTP/GTX/GTH/GTY) has measurably different
signal characteristics; can sometimes be inferred from root-port
performance counters independent of firmware spoofing.
Form Factors
Form Factor Description Detection
────────────────────────────────────────────────────────────────────
M.2 NGFF Key M Internal NVMe slot Dominant modern form;
physically invisible
M.2 + USB3 bridge M.2 board with FT601 Gaming PC sees only M.2
PCIe x1/x4 add-in Traditional add-in card More physically visible
External USB3 USB3-to-PCIe (legacy) Mostly obsolete
Combo boards DMA + HDMI capture + Complex device tree;
input injection HDMI activity is fingerprint
M.2 slot populations are partially auditable from software through
PCI topology, ACPI, SMBIOS, storage inventory, and vendor board databases.
SMBIOS slot records are often incomplete for M.2, so detection should
be probabilistic and board-model-aware.
pcileech Framework
Project Lineage
Five upstream repositories:
- pcileech: Host-side C application with attack modules
- pcileech-fpga: FPGA firmware in Verilog/SystemVerilog, per-board variants
- MemProcFS: Virtual filesystem mounting target memory as /proc-like tree
- LeechCore: Low-level device abstraction library
- vmm: Memory analysis engine (vmm.dll API)
Pipeline: FPGA → LeechCore → PCILeech attack modules / MemProcFS analysis
FPGA Firmware Architecture
Key modules:
- pcileech_pcie_a7.v / _us.v: Top-level Artix-7 / UltraScale integration
- pcileech_pcie_tlps128_bram_rdwr.v: 128-bit TLP source/sink (AXI-Stream)
- pcileech_pcie_cfgspace_shadow.v: Shadow config space in BRAM
- pcileech_cfgspace.coe: Init data (stock: Xilinx 10EE:0666)
- pcileech_bar_impl_zerowrite4k.v: Default BAR — absorbs writes, returns zero
- pcileech_bar_impl_loopaddr.v: Alternative BAR — echoes address
- pcileech_bar_impl_none.v: Disables BAR (returns UR)
- pcileech_pcie_cfg_a7.v: Config management via cfg_mgmt_*
- pcileech_mux.v: TLP multiplexer
- pcileech_fifo.v: Internal staging FIFO
Two key architectural choices:
1. Shadow config is spoofable but not spoofed by default.
.coe ships with placeholder Xilinx IDs. User must overwrite
with real donor's dump and resynthesize.
2. BAR controller is functionally inert.
zerowrite4k doesn't emulate device behavior.
Active BAR probing catches stock builds in one operation.
Host-Side MemProcFS
Mounts target memory as filesystem:
M:\
├── pid\1234\
│ ├── name.txt
│ ├── modules\ ← loaded module list
│ ├── handles\
│ ├── vad\ ← virtual address descriptors
│ ├── memmap.txt
│ └── minidump\
├── sys\
├── name\game.exe\ ← lookup by process name
└── forensic\
├── yara\
├── timeline\
└── registry\
One possible development/use pattern:
1. Development phase: MemProcFS, signature search, cross-references
→ slow, broad scanning to find entity manager / player array / view matrix
2. Execution phase: custom app via vmm.dll/LeechCore,
narrower periodic or batched reads of known offsets
Behavioral analysis can test for this pattern, but implementations may cache,
randomize, or use different access strategies.
Stock Firmware Fingerprints
Common or older vanilla pcileech-fpga configurations may exhibit the following;
verify the exact commit, FPGA IP configuration, and synthesized design:
- VID/DID 10EE:0666 (Xilinx placeholder)
- Xilinx 7-series PCIe IP signature bytes at characteristic offsets
- DSN Extended Capability absent or default
- No AER, LTR, ARI, ATS, or SR-IOV capabilities
- BAR0 mapped (DMA window); BAR1–5 disabled or all-ones
- BAR reads return zero (zerowrite4k) or echo address (loopaddr)
- MSI capability present but expected interrupts are not generated
- Config reads complete in deterministically uniform time
(BRAM lookup with fixed pipeline depth, near-zero variance)
- no observed ASPM transitions under a workload and policy that should enter
lower-power states
- AER correctable-error count stays at zero
- power state remains D0 under tested conditions
- Class Code matches donor placeholder but no class-specific behavior
Configuration Space Spoofing
Bridge vs Emulated Firmware
Bridge firmware:
Patches identity fields via Vivado's PCIe IP Core GUI
(VID, DID, Subsystem IDs, Class Code, sometimes DSN).
Fast to produce, but 7-series hard IP generates internal capability
blocks at characteristic offsets that retain FPGA-specific fingerprints.
Emulated (1:1) firmware:
Implements complete shadow Configuration Space in BRAM.
Entire 4 KB extended config space initialized from real donor device hex dump.
When OS issues CfgRd TLP, firmware responds from BRAM.
The design attempts to prevent IP-core defaults from appearing on the bus.
Common bugs in emulated firmware:
- First 16 bytes still come from IP block (mux priority)
- Type 1 config reads not intercepted
- Capability blocks bypassed in GUI still leak defaults
Shadow Configuration Space Implementation
Requirements:
1. Intercept incoming CfgRd0/CfgWr0 TLPs
2. Decode target offset
3. Look up value in BRAM
4. Build Completion TLP with correct Completer ID, status, payload
5. Send Completion through hard IP block
4 KB coverage at 4-byte granularity = 1,024 entries × 4 bytes = 4 KB BRAM.
Well within even T35's resources.
Overlay RAM and Writable Register Emulation
Real devices have writable registers. Firmware that returns correct
values on reads but drops writes creates detectable inconsistency.
Detection probe:
write Command[BME] = 1 → read Command[BME]
write Command[BME] = 0 → read Command[BME]
Real silicon: bit toggles. Naive shadow: bit stays at BRAM init value.
Overlay RAM merges at read time:
response = (base_value & ~writable_mask) | (overlay_value & writable_mask)
The catch: writable mask is register-specific:
- Command Register: different reserved bits than Device Control
- MSI Address Low: bits [1:0] reserved-zero
- BAR: type bits in [3:0] depend on I/O/memory, prefetchable
- Status Register: W1C bits — writing 1 clears, writing 0 no change
- AER Status: W1C across the board
Naive implementations with single global mask fail because
reserved-bit and W1C behavior diverges. Detection probes
W1C cases: write 0x00000000 to Correctable Error Status,
then write known-1 patterns, verify read-back semantics.
Donor Card Extraction
A common emulation strategy starts with a donor device and clones more than
VID/DID: configuration-space layout, capabilities, BAR masks, interrupt-table
layout, and device serial behavior where present. Completeness varies by design.
Extraction tools:
- lspci -d [VID:DID] -vvv -xxxx (full ECAM dump)
- setpci -s <BDF> ECAP_AER+0x4.L
- Direct ECAM mapping in kernel-mode tools
- VFIO passthrough + programmatic dump
Donor selection pitfalls:
- Duplicating hardware already in gaming PC → caught instantly
- Must match FPGA's actual PCIe capability (x16 Gen4 on Gen2 x1 fails)
- Silicon generation must align with claimed link speed
- Class-functional A/B testing detects non-functional donors
Firmware Sophistication Tiers
Tier Description Detection Difficulty
──────────────────────────────────────────────────────────────────
0 Stock Trivial — VID/DID blacklist
Unmodified upstream;
10EE:0666 IDs
1 Bridge Easy — signature residue,
.coe replaced with driverless device, BME clearance
donor VID/DID only
2 Shadow config Medium — R/W consistency probe
Full 4 KB shadow; catches silent write drops
no overlay RAM
3 Overlay RAM Medium-hard — BAR probe still fails;
Shadow + writable layer class-functional A/B fails
with per-register masks
4 BAR MMIO + MSI Hard — interrupt distribution analysis;
Donor-class BAR memory BAR-region content baselining
responder + MSI generator
5 Behavioral emulation Very hard — multi-session statistical
Latency jitter, ASPM, analysis required
AER counters, donor-
class-specific behavior
6 Private + randomized Currently undefeated by hardware-layer
Per-customer layout, signatures alone
capability shuffling,
custom hard-IP integration
Each tier transition corresponds to a defender technique
that closed the prior tier's escape hatch.
Cost-to-implement is nonlinear: 0–2 are public/trivial,
3 needs moderate Verilog, 4–5 need deep PCIe knowledge,
6 is sustained engineering.
Donor Exhaustion
Each detected donor class becomes nonviable. Remaining viable donors
trend toward obscure industrial cards — which themselves become
a behavioral signal on consumer gaming PCs.
Donor Class Detection Status
─────────────────────────────────────────────────────────
Wi-Fi adapters Heavily detected; class-spoof checks ubiquitous
Wired NICs "NIC with loaded driver but zero packets" test
NVMe SSDs Harder; detected via missing namespace activity
Audio codecs Lower bandwidth fits FPGA; class checks present
USB host controllers Child-device enumeration check breaks naive
Capture cards Harder (genuinely idle when no source)
Industrial / OEM SKUs Increasingly only viable; demographic signal
Server-class accel. Physically implausible on consumer boards
Detection at the PCIe Layer
Configuration Integrity
- VID/DID/SVID/SDID against known-real-silicon list
- Capability-chain walk: DWord-aligned Next pointers, no overlaps, no cycles
- Signature-residue scanning: Xilinx 7-series default byte patterns at
known relative offsets (Device Capabilities field bits, reserved bits,
VSEC vendor IDs)
- Capability presence consistency: expected capabilities must match the donor's
exact SKU, firmware, function, and configuration
- BAR mask verification: write 0xFFFFFFFF, compare size mask against donor
BAR Memory Read Probing
Send Memory Read TLPs to BAR ranges, validate responses by donor class:
NIC donor BAR0: register layout with receive/transmit ring descriptors,
interrupt mask, link status. Offset 0x00 returns specific bit pattern.
NVMe donor BAR0: NVMe controller registers — CAP (MQES, DSTRD,
MPSMIN/MPSMAX), VS, CC, CSTS, AQA, ASQ/ACQ, doorbells at 0x1000.
USB XHCI donor BAR0: Capability Registers (CAPLENGTH, HCSPARAMS, HCCPARAMS).
zerowrite4k returns all-zeros; loopaddr echoes address. These patterns are
conspicuous under donor-specific functional probes, although individual real
register ranges can legitimately contain zeros.
Tier-4 firmwares implement donor-class responders but usually only
cover registers checked at probe time, leaving others divergent.
R/W Consistency Probing
- Command Register: toggle Memory Space, I/O Space, Bus Master Enable
- Device Control: change MPS, MRRS, Error Enables
- MSI Control: toggle Enable, change Multiple Message Enable
- Walk every W1C bit (Status, AER Status): write 1s, confirm clear
- Walk reserved bits: write 1s, confirm read-back as 0
- Per-register writable masks must match donor
Tier-2 (no overlay) fails immediately.
Tier-3 (single global mask) fails on W1C and reserved-bit cases.
LTSSM and Link-State Validation
Sample PCIe Express Capability Link Status over time:
- Negotiated Width (Link Status[9:4]): consistent with donor deployment
and FPGA hard block capability
- Current Link Speed (Link Status[3:0]): track slot's actual speed
- A device can legitimately train below its maximum capability; compare the
result with slot topology, platform policy, signal quality, and matched donor
deployments
- DLL Active (Link Status[13]): should be 1 during operation
- Slot Clock Config (Link Status[12]): match real common-clock state
ASPM Behavioral Validation
Real devices claiming ASPM exhibit characteristic L0 ↔ L1 transitions.
Spoofed device anomalies:
- Claims and enables ASPM but shows no expected transition under a workload,
policy, and observation window known to exercise it
- Transitions with exit latency inconsistent with claimed value
- Does not reach L1.1/L1.2 when donor, platform, firmware policy, and workload
are verified to enable those substates
Sample Link Status "DLL Active" bit over time + PMC counters.
AER Baselining
- Departure from donor baseline: per-silicon correctable-error footprint
should be stable. Implausibly clean (zero correctables when donor
normally produces Bad TLP / Replay Timer Timeout) is anomalous.
- Implausible Header Log content (default/zeroed values)
- Inconsistent UR/CA responses to probes of unimplemented offsets
Completion Latency Fingerprinting
Completion latency can reflect memory, arbitration, buffering, power state,
link, driver, and workload behavior. A simplistic BRAM-backed emulator may show
lower variance, but real and emulated distributions can overlap.
Detection signal is distribution shape, not absolute mean.
Statistical methods:
- Kolmogorov–Smirnov test: compare empirical CDFs
- Tail estimators where sample size and distributional assumptions support them
- Anderson-Darling test: sensitive to tail differences
Choose the sample size from power/variance analysis, collect under controlled
conditions, compare with a matched donor reference, and validate any decision
threshold on held-out devices.
Random jitter alone need not reproduce donor behavior. Compare mean, variance,
tails, modes, autocorrelation, and responses to condition changes.
MSI/MSI-X Behavioral Validation
A device with MSI enabled, programmed Address/Data, an attached driver, and a
verified interrupt-producing condition should produce interrupts:
- Zero interrupts when driver should exercise device = anomalous
- Uniform arrival times may indicate a timer-driven generator, but legitimate
periodic workloads must be excluded
- Implausibly bursty patterns not matching donor class
Monitor via OS interrupt accounting, ETW/performance telemetry,
driver counters, kernel instrumentation.
Cheat-Phase Access Pattern Recognition
One possible workflow has a broad discovery phase followed by narrower,
periodic reads during use. Implementations can cache, randomize, batch, or avoid
these phases, and legitimate devices can also show periodic access.
Candidate execution features:
Temporal periodicity, address-space breadth, and alignment to game-frame
intervals, calibrated against matched benign device/workload behavior.
Distinguishing features:
- Fano factor
- Autocorrelation at frame intervals
- Address-space coverage entropy
Honeypot regions complement this when combined with:
IOMMU denial/fault logging, hypervisor-managed protected pages,
device-domain sandboxing, decoy IOVA mappings, or server-side
behavioral traps tied to fake game objects.
Hot-Plug and Link Disruption Events
Firmware swaps and donor reconfigurations require link renegotiation.
Three observable signals:
1. AER Surprise Down — uncorrectable fatal error logged when link
drops unexpectedly mid-session.
2. Slot Status hot-plug events — Presence Detect Changed,
Data Link Layer State Changed, MRL Sensor Changed.
Register via IoRegisterPlugPlayNotification with
EventCategoryTargetDeviceChange or EventCategoryDeviceInterfaceChange.
3. LTSSM re-training cycles — Link Training bit toggling,
transient Recovery state.
A device that surprise-downs then reappears with subtly different
Config Space (adjusted MSI layout, different latency profile,
different VID/DID) = fingerprint of mid-session firmware reload.
Detection at the IOMMU Layer
Fault-Rate Monitoring
Sample per-device fault counters from IOMMU fault-recording structure
(VT-d Fault Recording Registers, AMD-Vi Event Log) or from WHEA.
Pipeline:
1. Snapshot baseline at session start
2. Sample at intervals; compute per-device fault rate
3. Threshold-trigger additional PCIe probing on devices exceeding baseline
4. Aggregate evidence across signals before action
Domain Assignment Audit
Walk IOMMU domain assignments for anomalies:
- Devices on passthrough/identity domains when strict mode is active
- Devices in unexpectedly large IOMMU groups (poor ACS topology)
- Multiple devices sharing Domain ID when they shouldn't
ACS Topology Verification
Walk PCIe bridge topology between every endpoint and root complex.
For each bridge with ACS Capability:
- Verify Source Validation (SV) enabled
- Verify Translation Blocking (TB) enabled
- Verify P2P Request Redirect (RR) and Completion Redirect (CR) enabled
Missing or disabled ACS can limit isolation where peer routing is possible.
Assess the complete topology, root-complex behavior, firmware policy, and actual
IOMMU grouping before calling it an exploitable isolation hole.
IOMMU as Containment Primitive
Active containment when suspect device is identified:
1. IOMMU domain re-remapping:
Reprogram device's domain to sandbox memory instead of revoking access.
Requests may receive sandbox data or fault depending on mappings and device
behavior; validate OS/driver stability before using this response.
2. Bus Master Enable clearance:
Toggle Command[2] to 0. Effectiveness depends on platform enforcement,
device behavior, and alternate paths; monitor for restoration or races.
3. Downstream Port Containment (DPC):
When DPC is enabled on root port (Extended Cap ID 0x001D),
supported trigger conditions can place the downstream hierarchy into
containment. Verify the port status, traffic blocking, link recovery, and
platform-specific behavior; support is not universal.
4. Anti-cheat-owned device domain:
For device owned by AC driver, allocate and map only sandbox IOVAs,
never expose game memory.
5. Hypervisor-integrated enforcement:
Enforce policy above guest kernel by trapping IOMMU MMIO programming.
Requires privileged platform integration.
Hypervisor-Level Defense
EPT-Based Memory Protection
EPT translates Guest Physical Address (GPA) to Host Physical Address (HPA).
A hypervisor owning the EPT can:
- Mark game memory as read-execute-only in EPT, even if guest OS marks
read-write. Writes cause EPT violations the hypervisor traps.
- Hide pages by clearing EPT mappings.
- Implement watchpoints on specific GPA ranges.
IOMMU blocks DMA at device-to-memory boundary;
EPT blocks CPU access at guest-to-host boundary.
A cheat combining DMA card with kernel-mode payload faces both.
VBS, HVCI, and VTL Split
VBS creates Secure Kernel (VTL 1) alongside regular kernel (VTL 0)
in a Hyper-V partition. HVCI uses VTL 1 to enforce no executable page
in VTL 0 is simultaneously writable.
Anti-cheat interaction:
- Register VTL 1 callouts to validate guest state
- Attest against System Guard Secure Launch (DRTM) measurements
- Rely on HVCI to block BYOVD patterns
Combined VBS+HVCI+TPM+SecureBoot is assumed baseline for
serious anti-cheat threat models.
SMM Considerations
System Management Mode (Ring -2) runs in SMRAM, isolated from
the OS. SMM CPU memory accesses are not mediated by the device IOMMU, but
accessible data still depends on platform protections, memory encryption,
firmware design, and virtualization context.
A vulnerable SMI handler = path to arbitrary memory access
without IOMMU mediation.
Mitigations:
- Intel Boot Guard / AMD Platform Secure Boot (firmware signatures)
- SMI Transfer Monitor (STM): hypervisor-resident, treats SMM as
constrained guest; availability and deployment are platform-specific
- Runtime verification of SMM lockdown registers
PCIe IDE (Integrity and Data Encryption)
IDE adds link-level TLP protection: integrity (MAC-based, required)
and confidentiality (encryption, optional).
Incorporated into PCIe 6.0 base specification.
Valuable against: physical link interposers, malicious retimers/switches,
traffic tampering.
NOT a DMA-cheat silver bullet: cheat installed as the endpoint
still originates legitimate IDE-protected TLPs after key establishment.
IDE raises the bar for passive bus sniffing but endpoint identity,
IOMMU policy, ACS topology, ATS policy, and attestation remain required.
Trust property: without the attestation key or a break in the TPM/verification
chain, local software cannot forge a quote over arbitrary PCR values.
Flow:
1. Server sends nonce
2. Client calls TPM2_Quote(AIK, PCR_selection, nonce)
TPM computes PCR composite, builds TPMS_ATTEST, signs with AIK
3. Client sends Quote + AIK certificate chain
4. Verifier checks:
- AIK signature valid
- AIK certificate chains to trusted TPM manufacturer root
- EK on known-EK list (binds AIK to real TPM)
- Nonce matches (freshness, replay protection)
- PCR composite matches known-good value
A rootkit loading after measured boot cannot normally reset extend-only PCRs to
an arbitrary prior value through the standard TPM interface. A software
simulator cannot produce a quote verifiable under a trusted hardware-backed
attestation key, but a valid quote still covers only the selected measurements.
DRTM and Secure Launch
Dynamic Root of Trust for Measurement allows "late launch" —
trusted execution environment established after OS boot,
measurement captured into PCR[17].
Intel: GETSEC[SENTER] (TXT)
AMD: SKINIT (SVM extension)
CPU enters measured execution state, Secure Loader Block (SLB)
loaded and hashed into PCR[17], control transfers to
Measured Launch Environment (MLE).
Microsoft System Guard Secure Launch uses this to load HVCI's
hypervisor into measured state independent of SRTM chain.
Defender requests Quote including PCR[17] and matches against
known-good MLE measurement.
UEFI Pre-Boot DMA Integrity
Pre-Boot DMA Protection: firmware must isolate DMA-capable devices'
I/O buffers before ExitBootServices().
ACPI indicators:
- Intel: DMA_CTRL_PLATFORM_OPT_IN_FLAG in DMAR table flags
- AMD: DMA remap support bit in IVRS IVinfo field
Windows PCR[7] event: firmware extends EV_EFI_ACTION with
"DMA Protection Disabled" when IOMMU/Kernel DMA Protection
is disabled, providing attestation hook.
Combined picture:
PCR[0]/PCR[7] anchor firmware and DMA-protection policy,
ACPI tables describe runtime IOMMU config,
documented DMA interfaces show what OS actually remaps,
attestation ties local claims to remote-verified known-good policy.
Layered Detection Pipeline
Pre-Game Environmental Verification
- IOMMU active and applied to DMA-capable PCIe paths
- Interrupt Remapping enabled
- Secure Boot enabled
- VBS/HVCI active
- TPM 2.0 present and provisioned
- Attestation Quote validates against expected policy
- BIOS/UEFI version not in known vulnerable pre-boot DMA list
- ACS topology walk: all relevant bridges enforce SV, TB, RR, CR
PCIe Inventory Pass
- Enumerate all PCIe devices via PnP tree
- Full 4 KB config-space dump for each
- Check device problem codes (DEVPKEY_Device_ProblemCode)
- Cross-reference SMBIOS slot inventory with populated devices
Configuration Integrity Per Device
- VID/DID/SVID/SDID against known-good list
- Capability-chain walk and validation
- Signature-residue scan
- BAR mask verification
- R/W consistency probing
- Compare against per-donor reference database
Behavioral Sampling During Play
- Periodic Link Status reads (LTSSM, ASPM transitions)
- AER counter snapshots
- Per-device interrupt rate and distribution
- Per-device IOMMU fault rate
- BAR-region content sampling for class consistency
Statistical Analysis Over Session
- Latency distribution comparison (KS test, Hill estimator)
- Interrupt arrival distribution
- ASPM transition rate
Cheat-Phase Detection
- Honeypot region access
- Memory access frequency / locality classifiers
Containment Before Verdict
Each detection produces evidence, not a verdict.
Verdict informed by:
- Multi-signal correlation with measured joint error rates; correlated
signals can share the same false-positive cause
- Server-side aggregation across sessions
- Behavioral verification (input timing, gameplay statistics)
While verdict accumulates, containment protects the live match:
IOMMU re-remapping to sandbox, BME clearance, or EPT-level
game-process protection degrades cheat effectiveness in real time.
Apply research-rigor when converting these
signals into a claim or response. Validate baselines per device, firmware,
platform, topology, driver, and power state; preserve raw captures and test
benign alternatives before attribution.
Realistic Limits
A firmware that:
- Clones donor byte-for-byte (full 4 KB config + all capabilities)
- Implements donor-class BAR MMIO, MSI generation, overlay RAM
- Adds completion-latency jitter matching donor distribution
- Generates plausible AER correctable-error rates
- Transitions through ASPM states like the donor
- Uses donor not present in gaming PC and not on blacklists
- Operates only within driver-mapped IOMMU domains (legitimate-path exfil)
- Avoids honeypot regions through gameplay-aware address whitelisting
...can evade the listed PCIe-layer and IOMMU-layer signatures when each is used
in isolation and the emulation matches the defender's tested dimensions.
This is why external trust anchors are required:
TPM attestation, measured boot, and server-side correlation operate
outside the "spoof a PCIe endpoint" problem.
A device cannot forge a TPM Quote signature without the attestation key, but a
valid Quote attests only the selected PCR values and nonce. It does not by
itself prove the absence of a runtime DMA device or the current IOMMU mapping.
The verifier must validate the event log and a policy covering measured
firmware, DMA-protection events, Secure Boot, VBS/HVCI, and IOMMU configuration,
then obtain separate evidence for unmeasured runtime state.
Layering PCIe, IOMMU, hypervisor, and attestation controls raises attacker cost;
whether it exceeds attacker value is an environment-specific economic claim,
not a technical guarantee.
Forensic Evidence Capture
What to Capture
Artifact Source Purpose
──────────────────────────────────────────────────────────────────────────────
Full 4 KB config dump Bus interface / ECAM Donor ID post-hoc
Capability chain walk Parsed from config Capability presence
PCIe link state history Link Status over session LTSSM anomaly evidence
MSI/MSI-X arrival timeline OS interrupt telemetry Rate claim refutation
AER correctable counts AER capability registers Baseline outlier evidence
IOMMU fault log entries WHEA/ETW, Driver Verifier Invalid-DMA evidence
IOMMU domain assignments IOMMU manager state walk Passthrough anomaly
ACS bridge state Bridge enumeration Isolation assessment
Honeypot access record Hypervisor EPT trap log Unauthorized read evidence
TPM PCR snapshot TPM Quote API Boot-chain attestation
MCFG / DMAR / IVRS tables ACPI subsystem Platform config baseline
SMBIOS slot inventory DMI subsystem Slot-population audit
BIOS version + patch level SMBIOS Pre-Boot DMA fix verify
Latency-distribution hists Per-session sampling Statistical fingerprint
Multi-Signal Correlation
Strongest evidence packages combine:
1. Hardware-layer signal (config space, BAR, link state)
2. Behavioral-layer signal (interrupt distribution, IOMMU fault rate, honeypot)
3. Temporal correlation (hardware signal preceded behavioral by plausible interval)
No signal count guarantees a target false-positive rate. Establish independence
or model dependence, validate the joint decision rule on representative benign
systems, and report confidence bounds plus expected appeal volume.
PCIe Protocol Captures
A PCIe protocol analyzer (interposer) can provide high-fidelity evidence at its
observation point: TLP-level captures with analyzer-specific timestamp accuracy.
Commercial analyzers capture every TLP, DLLP, and physical-layer ordered set.
Traces can be replayed to confirm fingerprinting findings.
Cost and deployment complexity limit routine use. For high-impact cases,
protocol-level captures from an independent lab can materially strengthen the
record, but capture coverage, analyzer configuration, and interpretation still
need validation.
Thunderbolt / USB4 DMA
Attack Surface
- Thunderbolt 1-4 / USB4 provide direct PCIe tunneling
- Hot-plug capable: device can be attached at runtime
- Pre-boot DMA: device has memory access before OS loads
- Thunderbolt Security Levels:
- SL0 (None): no security, legacy mode
- SL1 (User Auth): user must approve new devices
- SL2 (Secure Connect): device must match previously approved UUID
- SL3 (No PCIe tunneling): completely disables DMA
- Maintain two sets of page tables (two CR3 values):
- "Clean" CR3: legitimate page tables visible to anti-cheat
- "Shadow" CR3: modified page tables with cheat-accessible mappings
- Swap CR3 before/after anti-cheat inspection windows
- Combine with EPT manipulation for hypervisor-level split
Split TLB Techniques
- Desync instruction TLB (iTLB) and data TLB (dTLB):
- Execute code from one physical page
- Read data from another physical page at same virtual address
- Requires precise TLB invalidation control
- Hypervisor can create EPT-based split: execute on page A,
read on page B, at same GPA
- Anti-cheat mitigation: TLB flush + re-walk, serializing instructions
The main README contains thousands of curated links organized by category. When users ask for specific tools, projects, or implementations, retrieve and reference the appropriate sections from this source.
2. Repository Code Details (Archive)
For detailed repository information (file structure, source code, implementation details), the project maintains a local archive. If a repository has been archived, always prefer fetching from the archive over cloning or browsing GitHub directly.
Identify the GitHub repository the user is asking about (owner and repo name from the URL).
Construct the description URL: replace {owner} with the GitHub username/org and {repo} with the repository name.
Fetch the description file — it contains a short, human-readable summary of the repository's purpose and contents.
If the fetch returns a 404, the description has not been generated yet; fall back to the README entry or the archive.
Priority order when answering questions about a specific repository:
Description (quick summary) — fetch first for concise context
Archive (full code snapshot) — fetch when deeper implementation details are needed
README entry — fallback when neither description nor archive is available
Compiled wiki
Prefer the compiled domain overview at wiki/overviews/dma-attack.md (see wiki/index.md and wiki/AGENTS.md) before re-deriving synthesis from raw README/archive material.
