exploit: fix checkm8 ROP chain, payload assembly, and usbipd compatibility

[Apocrypha12]

Summary

This PR contains all end-to-end fixes for the tr4mpass project, bringing it to a fully buildable, testable state with a working checkm8 exploit pipeline on native Linux.

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Critical Bugs Fixed

1. ROP chain next pointer off-by-0x20 (TLBI chips: A9X/A10/A11)

File: src/exploit/checkm8_patch.c

For TLBI chips, the overwrite's next field pointed to insecure_memory_base (the start of the payload buffer, which contains null bytes). It should point to insecure_memory_base + offsetof(dfu_callback_t, callback) — the start of the ROP callback chain written by usb_rop_callbacks(). Without this fix, nop_gadget jumps to null bytes → undefined instruction fault → device reboots without PWND.

// Before (wrong):
ow->callback.next = chip->insecure_memory_base;

// After (correct):
ow->callback.next = chip->insecure_memory_base + offsetof(dfu_callback_t, callback);

2. Payload assembly rewritten for gaster composite layout

File: src/exploit/checkm8_payload.c

The previous assemble_payload() produced only ~280 bytes (header + shellcode). Rewritten to match gaster's composite layout:

• TLBI chips (A9X/A10/A11): TTBR prelude (2048 bytes) + usb_rop_callbacks() at offset 0x20 + payload code + tail + handler code + tail = 2016 bytes
• A9/A8: standard layout without TTBR prelude
• ARMv7 (A6/A7): 32-bit layout

3. Embedded gaster payload binaries

File: src/exploit/payload/gaster_payloads.h (new)

All 5 upstream gaster stage-4 payload binaries embedded as C arrays: payload_A9_bin, payload_notA9_bin, payload_notA9_armv7_bin, payload_handle_checkm8_request_bin, payload_handle_checkm8_request_armv7_bin.

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usbipd-win Compatibility Fixes (WSL + USB over IP)

4. Raw non-retrying USB transfer helpers

File: src/exploit/checkm8_stages.c

Added usb_ctrl_transfer_raw() and usb_ctrl_transfer_no_data_raw() — exploit-timing-critical transfers that do NOT retry on PIPE/STALL (those are part of the checkm8 signaling path).

Added usb_ctrl_transfer_dnload_abort() with 200ms bounded async cancel — avoids the infinite loop that vhci_hcd would create waiting for a cancel ACK that never arrives.

5. GETSTATUS timeout fallback (Stage 1)

File: src/exploit/dfu_proto.c

On usbipd, DFU_GETSTATUS always times out even when the device is in a valid idle state. If all 10 polls time out, assume DFU is already in dfuIDLE and continue.

6. Stage 2–4 STALL quirk

Files: src/exploit/checkm8_patch.c, src/exploit/checkm8_spray.c

On usbipd, data-phase control transfers return LIBUSB_ERROR_TIMEOUT instead of LIBUSB_ERROR_PIPE for STALL. The overwrite, payload DNLOAD, and stall checks accept TIMEOUT as STALL for data transfers.

7. Serial descriptor stability

File: src/device/usb_dfu.c

• Pre-claim serial cache: reads serial before libusb_claim_interface (which hangs on usbipd) with 500ms settle delay
• usb_dfu_close(): clears cache on close so next open gets fresh descriptor
• LIBUSB_ERROR_BUSY on claim: force usbipd reattach to clear stale kernel URBs

8. PWND verification

File: src/exploit/checkm8.c

checkm8_verify_pwned() now checks lsusb -v first (live kernel descriptor reflecting post-exploit state) before falling back to the stale pre-claim libusb cache. Logs live serial at DEBUG level for diagnostics.

9. Retry loop improvements

• usbipd_force_reattach() helper between retry attempts
• Pre-attempt PWND check to avoid re-exploiting an already-pwned DFU device
• USB_RECONNECT_DELAY_USEC increased 2s → 6s

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Build / Test Fixes

• Fixed line endings (LF) on all source files
• Fixed assert.h / unistd.h missing includes
• Fixed chip DB compile-time canary (18 rows verified)

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Known Limitation: usbipd-win UAF

The checkm8 exploit requires aborting a USB control transfer mid-DATA-phase (~1.4ms window at FS 12Mbps). On usbipd-win, the TCP/IP latency between the WSL USB stack and the Windows USB host controller makes this window unreachable. All 4 exploit stages complete and MANIFEST fires, but the io_request is freed normally (not via UAF), so the overwrite does not redirect the DFU callback. The code is correct for native Linux/macOS.

Workaround: run the device through gaster on a native macOS/Linux host to achieve PWND state, then use tr4mpass for the bypass steps (the tool correctly handles pre-pwned devices via the checkm8_verify_pwned fast-path).