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Filename : 8086:7360
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#!/bin/bash

# SPDX-License-Identifier: CC0-1.0
# 2024 Thomas Vogt
#
# RPC-powered Intel XMM7360 (8086:7360) FCC unlock

if [[ "$FCC_UNLOCK_DEBUG_LOG" == '1' ]]; then
    exec 3>&1 4>&2
    trap 'exec 2>&4 1>&3' 0 1 2 3
    exec 1>>/var/log/mm-xmm7360-fcc.log 2>&1
fi

# require program name and at least 2 arguments
[ $# -lt 2 ] && exit 1

# first argument is DBus path, not needed here
shift

# second and next arguments are control port names
for PORT in "$@"; do
  # support for XMM7360 has been added in 5.18
  # match port type, assuming Linux 5.14 and newer
  grep -q XMMRPC "/sys/class/wwan/$PORT/type" 2>/dev/null && {
    XMMRPC_PORT=$PORT
    break
  }
done

# fail if no XMMRPC port exposed
[ -n "$XMMRPC_PORT" ] || exit 2

DEVICE=/dev/${XMMRPC_PORT}

log() {
    echo "$1"
}

error() {
    echo "$1" >&2
}

reverseHexEndianness() {
    num="$1"
    printf "%s" "${num:6:2}${num:4:2}${num:2:2}${num:0:2}"
}

littleEndianToDec() {
    printf "%d" "0x$1"
}

bigEndianToDec() {
    littleEndianToDec "$(reverseHexEndianness "$1")"
}

readNBytesAsHex() {
    data=$(head "-c$1" <&99 | xxd -p -c0 | tr -d '\n')
    printf "%s" "$data"
}

writeHexAsBinary() {
    printf "%s" "$1" | xxd -r -p >&99
}

readResponseAsHex() {
    length_hex=$(readNBytesAsHex 4)
    length=$(bigEndianToDec "$length_hex")
    content=$(readNBytesAsHex $length)
    printf "%s" "$length_hex$content"
}

rpc_command() {
    exec 99<>"$DEVICE"
    writeHexAsBinary $1
    answer=$(readResponseAsHex)  # ignore "async-ack" response
    answer=$(readResponseAsHex)
    printf "%s" "$answer"
    exec 99>&-
}

VENDOR_ID_HASH="3df8c719"

for i in {1..3}; do
    log "Attempt #${i} to unlock WWAN modem"

    log "Requesting FCC lock state from modem"
    # --> (async) csi-fcc-lock-query-req
    RESP=$(rpc_command "1c00000002040000001c02040000018e11000101020411000101020400000000")
    MODE=$(littleEndianToDec "${RESP: -8}")
    STATE=$(littleEndianToDec "${RESP: -20:8}")

    log "Got response from modem: state=$STATE, mode=$MODE"

    if [ "$MODE" = "0" ]; then
        log "FCC lock is deactivated, nothing to do."
        exit 0
    fi

    if [ "$STATE" != "0" ]; then
        log "FCC already unlocked, nothing to do."
        exit 0
    fi

    log "Requesting challenge from modem"
    # --> (async) csi-fcc-lock-gen-challenge-req
    RESP=$(rpc_command "1c00000002040000001c02040000019011000101020411000101020400000000")
    HEX_CHALLENGE=$(printf "%s" "${RESP: -8}")

    log "Got challenge from modem: $HEX_CHALLENGE"
    REVERSE_HEX_CHALLENGE=$(reverseHexEndianness "${HEX_CHALLENGE}")
    COMBINED_CHALLENGE="${REVERSE_HEX_CHALLENGE}${VENDOR_ID_HASH}"
    RESPONSE_HASH=$(printf "%s" "$COMBINED_CHALLENGE" | xxd -r -p | sha256sum | cut -d ' ' -f 1)
    REVERSED_RESPONSE=$(reverseHexEndianness "${RESPONSE_HASH:0:8}")

    log "Sending hash to modem: $REVERSED_RESPONSE"
    # --> (async) csi-fcc-lock-ver-challenge-req
    RESP=$(rpc_command "1c00000002040000001c020400000192110001010204110001010204${REVERSED_RESPONSE}")
    UNLOCK_RESPONSE=$(littleEndianToDec "${RESP: -8}")

    if [ "$UNLOCK_RESPONSE" = "0" ]; then
        error "Unlock failed."
    else
        log "FCC unlock successful (response $UNLOCK_RESPONSE)"
        exit 0
    fi

    sleep 0.5
done

exit 2