reverse-engineering-anything/docs/firmware-analysis.md

Firmware analysis

REA accepts Binwalk 3.1.x for region inspection and Unblob 26.6.x for explicit extraction. The report parsers are verified with Binwalk 3.1.0 and Unblob 26.6.4. Another build on those lines is accepted, the observed version is reported, and a limitation records that the parser was not verified against that build. This first firmware milestone is verified on Linux x64. No device, root privilege, mount, emulation or execution of extracted programs is needed. Arbitrary firmware bytes do not pass native executable admission; select a returned ELF separately for supported Ghidra analysis.

On Linux, Binwalk and Unblob run as REA-owned processes and require a procps-compatible ps on REA's PATH; see the shared Linux process prerequisite.

Caller-supplied tools

Provide existing tools using absolute executable paths, scoped to your shell:

export REA_BINWALK_COMMAND=/absolute/path/to/binwalk
export REA_UNBLOB_COMMAND=/absolute/path/to/unblob

REA does not install these tools, their dependencies or system packages. It checks the tool's --version banner when executing a request. Binwalk must print binwalk <version> and Unblob must print the version alone. Inspection and extraction have independent prerequisites; one does not require the other. Both require util-linux prlimit, normally /usr/bin/prlimit; override its absolute path with REA_FIRMWARE_PRLIMIT_COMMAND if needed. rea doctor does not currently inspect firmware readiness. Engine selection/version checks run when the firmware operation is requested; successful general doctor checks do not establish firmware tool or external-extractor availability.

REA retains at most 8 MiB of combined stdout and stderr per command. Exceeding that diagnostic budget stops analysis with an explicit truncated-output error; child process limits do not bound parent-side pipe retention. Completed commands drain their output streams before recording diagnostics. Failed worker cleanup retains the worker and workspace for retry before another request or at shutdown.

Unblob needs the external extractor for the selected format on its inherited PATH: for example, debugfs for ext2/ext3/ext4. Its default Landlock sandbox and skip rules stay enabled. Sandbox startup failures remain actionable errors; REA does not retry with --no-sandbox. Missing extractors reported in a valid analysis report retain partial results and dependency names inline.

Upstream sources are preserved unmodified as optional pinned submodules:

git submodule update --init third_party/binwalk third_party/unblob

Normal REA builds and npm packages do not include or build these sources or engine binaries. See upstream provenance.

Windows submodule checkout

On Windows, the Unblob checkout stops with error: invalid path. Several upstream test fixture names under tests/integration/ contain characters, trailing dots, or trailing spaces that NTFS does not allow; REA does not use those fixtures. Keep the clone, exclude that directory, and retry from the repository root in PowerShell:

git -C third_party/unblob config core.protectNTFS false
git -C third_party/unblob sparse-checkout set --no-cone '/*' '!/tests/integration/'
git submodule update third_party/unblob

Both settings are required. While core.protectNTFS is enabled, Git for Windows also rejects index paths that the sparse pattern excludes; the pattern keeps the invalid names out of the worktree. The setting applies only to the Unblob submodule. In Git Bash, prefix the sparse-checkout command with MSYS_NO_PATHCONV=1; otherwise !/tests/integration/ is rewritten as a Windows path.

The extraction destination must be absent with an existing writable parent. REA checks that selection before starting an engine and still acquires it exclusively during publication. Invalid sources and destinations identify the caller argument; failures inside an acquired workspace keep their own cause. Published file relative_path preserves producer spelling for lineage; path uses the writer's actual normalized filename. An extracted filename that cannot be represented losslessly as UTF-8 fails publication explicitly with its raw name bytes in hexadecimal instead of silently omitting the entry. Unpublished symlinks retain the extracted tree's target bytes in lowercase link_target_hex; link_target is null when those bytes are not valid UTF-8. Older retained Evidence may omit the hexadecimal field. Unblob may have rewritten the target before REA observed it, so these bytes are not necessarily those stored in the firmware image.

CLI and MCP

rea inspect-firmware-regions /path/to/firmware.bin
rea extract-firmware /path/to/firmware.bin /path/to/new-output
rea extract-firmware /path/to/firmware.bin /path/to/selected-output \
  --offset 64 --length 4096 --max-depth 3

The corresponding MCP tools accept the same intent:

{
  "name": "inspect_firmware_regions",
  "arguments": { "path": "/path/to/firmware.bin" }
}

{
  "name": "extract_firmware",
  "arguments": {
    "path": "/path/to/firmware.bin",
    "output_directory": "/path/to/new-output",
    "range": { "offset": 64, "length": 4096 },
    "max_depth": 3
  }
}

Both return Evidence with the original path and SHA-256, raw producer reports, actual executable path/digest, version and limitations. Binwalk signature UUIDs and Unblob blob IDs are producer-local identities; compare content hashes and source ranges across runs. A matching version does not attest an installed build's source revision, so that field remains unknown.

Interpret the results

• Region offsets refer to bytes in the original firmware. reported_size preserves Binwalk's output; size_basis=provider_reported_validation_unknown reflects that Binwalk can replace unknown lengths with the next signature or EOF before serialization. Neither a signature nor its confidence byte proves a valid partition, encryption or runtime behavior.
• Extraction returns regular file paths, independently verified SHA-256 values, producer hashes when available, chunks, diagnostics and task derivations. Unblob's task report is unordered; REA resolves relationships by paths and blob IDs. Logical references use $input, $output, or $output/<relative-path> so a real file named $input stays distinct from the original input. Chunk offsets belong to the task's input file. Only chunks in the selected input have a known root_file_range, adjusted by the selected offset.
• Decompressed children have unknown original byte ranges and runtime addresses. Task lineage does not establish a byte-for-byte mapping through decompression.
• partial marks unknown/encrypted chunks, selected input bytes outside all reported chunk intervals, reported extraction problems, unpublished links/special files or reached depth limits. complete means the selected input is covered by reported chunk intervals and the engine finished its configured extraction without those reported conditions; default skip rules and format coverage still apply. It does not establish complete firmware reconstruction.
• extraction_gaps makes those conditions recoverable: a row identifies an unextracted region or a failed task/stage. A chunk retains its identity and byte range, plus its original-file range when it belongs to the selected input. unclassified-range rows identify selected input intervals with no reported chunk; their provider identity and handler stay null. An empty chunk inventory therefore cannot establish complete extraction of a nonempty selected input. A multi-file stage retains its reported ID and handler with unknown byte ranges; a standalone task failure keeps unavailable stage identity null. Rows retain exact dependency names from the producer's missing-dependency reports; an accepted report with no names remains a failure with unknown dependencies; no executable identity or specific installation step is inferred. Each row's continuation_id references one instruction in extraction_continuations, so many regions share recovery prose without losing any region identity. Instructions use already configured capabilities where one exists. Every extraction rerun requires a fresh absent output_directory, preserving the prior evidence. Unblob's declared ERROR severity establishes an extraction failure, including standalone UnknownError task exceptions. Warnings and resolved extraction problems remain diagnostics with partial coverage; they do not establish failed extractor stages. Standalone errors do not acquire a nearby chunk's handler or byte range. Nested unknown chunks use inspect_firmware_regions on the actual published child rather than repeating the same extraction with unchanged handlers. Inspection requires separately configured Binwalk (REA_BINWALK_COMMAND); without it, the inspection step is unavailable and the region remains unexamined. A listed gap does not mean the target is corrupt or that a retained region is empty; REA installs nothing.
• The destination must be absent, absolute, with an existing parent. Publication uses exclusive, symlink-resistant writes and durable digest readback. Existing destinations are never overwritten. This is not an atomic directory rename: a new tree can be visible while files are written. Failed uncommitted output is rolled back. Symlinks and special files are recorded without publication; empty directories, ownership and executable permission bits are not reproduced.

Select a verified native child for the existing tools:

{
  "name": "open_binary",
  "arguments": {
    "path": "/path/from/extraction/usr/bin/program",
    "provider_id": "ghidra"
  }
}

Then use analyze_function, inspect_native_api or the other native primitives. Native architecture and executable validation still apply. Generic MIPS ELF and RISC-V ELF lanes are separate documents with their own admission boundaries. This milestone does not add PPC decompilation, raw flash load profiles, bootloader/device tree semantics, vulnerability scanning, emulation or hardware runtime capture.

Resource and lifecycle policy

• Nonempty regular firmware inputs: at most 128 MiB, copied and hashed into a private workspace before analysis. Growth beyond that allowance during copying receives the same typed input refusal as an already oversized file. Supply a stable copy within the allowance. No in-place source modification.
• One queued heavy operation per provider instance; Binwalk one thread and Unblob one worker. No automatic parallel extraction engines.
• Analysis defaults to 120 seconds, from tool resolution and input snapshot through inspection and its final private-workspace cleanup, or extraction through report consumption and inventory, excluding queue waiting and retained cleanup admission. Inspection has no publication phase. Select analysis_timeout_ms in either MCP operation or --analysis-timeout-ms in either CLI command for slower analysis. Current results retain the actual budget; an absent historical value means unknown. Extraction publication and its final cleanup start a separate 120-second budget; select publication_timeout_ms in MCP or --publication-timeout-ms in CLI for a slow destination. Valid budgets are integers from 1 through 2,147,483,647 ms (the timer representation limit). Publication timeouts identify their phase and verified file progress; verified writes before atomic commit are not a claim that output remains published after rollback. Caller cancellation applies to both phases and final cleanup. Phase handoff, publication commit and final completion also check monotonic elapsed time, so delayed timer callbacks cannot revive an expired budget.
• Analysis timeout recovery names the selected budget and the analysis control, not the later publication control. Keep the client call timeout above analysis, publication and cleanup headroom; keep the input/range/question unchanged. Resolve any reported incomplete cleanup before retrying. Raising wall time does not raise fixed CPU, memory, report, diagnostic or input limits.
• Inherited 1 GiB per-process address-space limit, 120 CPU seconds and zero core-dump allowance through prlimit.
• JSON reports: at most 8 MiB and valid UTF-8; malformed encoding and oversized reports fail without repairing or truncating producer data. Exit status 0 is not an empty result: a missing, empty, malformed or oversized report fails with unreadable_output, its report_state, the command, exit status and captured output. REA does not retry automatically. Diagnostic output is bounded with exact captured byte counts.
• Default staging budget: 256 MiB and 10,000 entries, configurable using max_output_bytes / max_output_files (CLI --max-output-bytes / --max-output-files). Exceeding either selected staging budget returns a nonretryable resource constraint naming the selected limit. Depth defaults to 3, allowed range 1–10.

Staging budgets are polled and rechecked after exit; short-lived overshoot is possible. The per-file process limit is the larger of the selected payload budget and the fixed report/diagnostic file allowances, so a small payload selection still permits the mandatory report. A tighter inherited host limit still applies. The inherited file-size limit bounds each file, not total storage; address-space limits are per process, not an aggregate memory quota. Worker count is not CPU affinity for every external extractor. These limits do not claim cgroup/container containment. Cancellation cleans the owned process group before removing its workspace; uncertain cleanup retains resources and blocks further operations in that provider instance.

Verification

Generate small public, source-derived fixtures into ignored _reference/:

npm run fixtures:firmware
npm run verify:firmware

Fixture generation requires existing Python 3 and a host C compiler (cc); override with REA_FIRMWARE_PYTHON / REA_FIRMWARE_CC. The independent oracle records gzip offset/length and extracted file hashes. Real verification checks CLI/MCP, full-file and selected-range extraction, unknown chunks, depth limits, content parity and unchanged source bytes. No binary fixture is committed.

The optional missing-extractor lane asserts dependency names and the owning handler in extraction_gaps. Those assertions must be run against the pinned Unblob release to establish real-provider coverage; synthetic producer fixtures alone do not verify Unblob's report nesting or stage identities. The gap ownership claims remain unverified against real Unblob until that lane runs.

Additional lanes are explicit, so the base lane stays small:

# Existing mke2fs and debugfs required; put debugfs on the scoped PATH.
REA_FIRMWARE_VERIFY_EXT4=1 npm run fixtures:firmware
REA_FIRMWARE_VERIFY_EXT4=1 npm run verify:firmware

# Existing Ghidra 12.x (>=12.1) and its declared JDK required.
REA_FIRMWARE_VERIFY_GHIDRA=1 npm run verify:firmware

REA_FIRMWARE_MKE2FS_COMMAND selects the optional ext4 fixture producer. REA_FIRMWARE_FIXTURE_ROOT selects generated data storage. REA_FIRMWARE_TEST_ENTRYPOINT can select an isolated installed npm package's scripts/rea.mjs to verify the packaged CLI/MCP workflow. Real coverage here is generated gzip/USTAR/ext4 with a Linux x64 ELF child; SquashFS, UBIFS, proprietary firmware, other hosts and architectures remain unverified.

Inspect ESP images

Use inspect-artifact / inspect_artifact on an ESP32-family app or bootloader image, such as an OTA download or app partition, for its chip, classified segments, checksum and SHA-256 results, descriptor and Secure Boot v2 signature blocks. extract-artifact / extract_artifact writes one file per segment and signature block. Reading is portable and needs no external tool. See ESP images.

Inspect ESP flash dumps

Use the same tools on a whole-flash dump, such as esptool read-flash 0 ALL output. The inventory reports the bootloader, the partition table and how it was found, each partition with its declared type, flags and digest, ESP image facts for the bootloader and each app partition, and the OTA records with a derived selection; the running partition stays unknown. Extraction writes each partition, nvs_keys included, as an ordinary file. For a dump that does not start at flash address 0, select esp-flash-image with flash_offset. See ESP flash images.

Inspect extracted devicetrees

Use inspect_devicetree / rea inspect-devicetree on an extracted DTB for its node/property tree, reservations, hardware summary and selected phandle relationships. FDT v16/v17 inspection is portable and requires no external tool or disassembler.

Inspect Intel HEX and S-record images

Use inspect-artifact / inspect_artifact on an Intel HEX or Motorola S-record file for its address regions, declared start address and record facts, then extract-artifact / extract_artifact for one raw file per region. Decoding is portable and requires no external tool. See Intel HEX and S-record images.

Inspect U-Boot legacy uImages

inspect-artifact / extract-artifact recognize a legacy uImage by its 0x27051956 magic and inventory it without running or decompressing it. The root facts record the 64-byte header (architecture, OS, type, and compression as raw values and names, load and entry addresses, image name, and timestamp) with the header and data CRC32 verified; the stored payload is extractable as payload.bin, and multi-file and script images additionally expose each sub-image as image-<n>.bin from the stored size table. Declared addresses are facts from the header, not proven entry points, and compressed payloads stay as stored. Intel HEX/S-record and FIT images are separate readers and are not covered here. See U-Boot legacy uImage for component padding, preserved names, resource policies and verification scope.

Inspect UF2 and DfuSe images

Use inspect-artifact / inspect_artifact on a UF2 file for each familyID's address regions and its block numbering, or on a DfuSe file for its targets, elements and DFU suffix, then extract-artifact / extract_artifact for one raw file per region or element. A DfuSe suffix CRC mismatch follows integrity_policy. Decoding is portable and requires no external tool. See UF2 and DfuSe images.

Inspect U-Boot FIT images

Use inspect-artifact / inspect_artifact on a U-Boot FIT (.itb) for its images, declared load and entry addresses, configurations and verified hashes, then extract-artifact / extract_artifact for one raw file per image. Decoding is portable and requires no external tool. See U-Boot FIT images.