CAN FIREWALL

There are two tables, IVI2VEH and VEH2IVI, specifiying rules for traffic going from the IVI to the vehicle and from vehicle to IVI.

Each one of the two tables has a number of rules.

Each rule has a numberic ID. Rules are executed in order of ascending IDs.

Each rule has an Frame ID mask and a Frame ID filter, applied according to the standard CAN bus filter principle, as described here.

Below is pseudo code for frame processing.

process_frame(frame_id, payload) {

  // Traverse all rules
  for (i in rules) {
    masked_id = (frame_id & rules[i].id_mask);

    // If the masked out ID is 0, we have a hit. Process
    if (!masked_id) {
      process(frame_id, input, rules[i].action,
	          rules[i].id_operand, rules[i].data_operand);
      return;
    }

    // Check if we have a hit on the masked ID and the
	// ID filter.
    // If so, we have a hit and will process
    if (masked_id & rules[i].id_filter) {
      process(frame_id, input, rules[i].action,
	          rules[i].id_operand, rules[i].data_operand);
      return;
    }

    // No hit. Try next rule
  }

  // No rule matched. Forward unmodified frame
  process(frame_id, input, ID_AND_DATA_AND,
          0xFFFFFFFF, 0xFFFFFFFFFFFFFFFF);

  return ok;
}

Below is an example of a rule table.

ID	IdMask	IdFilter	Action	IdOperand	DataOperand
1	0xFFFFFFFF	0x00000012	ID_AND_DATA_OR	0x00FFFFFF	0x000000FFFFFFFFFF
2	0xFFFFFFF0	0x00000120	ID_SET_DATA_SET	0x01234567	0x0123456780ABCDEF
99	0x00000000	0x00000000	BLOCK	0x00000000	0x0000000000000000

• RULE 1
  Rule ID 1 specifies will filter out the lower all bits of the CAN frame ID and match those against the specific ID 0x12, thus intercepting all CAN frames with the exact ID of 0x00000012.
  An intercepted frame will be forwarded to the other side after ANDing the incoming Frame ID with 0x00FFFFFF, and then ORing the data payload with 0x000000FFFFFFFFFF.
  Once the intercepted frame has been forwarded, the next frame is processed.

• RULE 2
  

  Rule ID 2 is evaluated for all frames not intercepted by Rule 1 above. The rule will mask the incoming CAN frame ID against 0xFFFFFFF0 and filter the result against 0x00000120, intercepting all CAN frames between 0x00000120 and 0x0000012F.
  For each frame intercetpted by rule 2, a fixed frame will be sent to the other side with the frame ID 0x01234567 and payload 0x0123456780ABCDEF.

• RULE 99
  Rule 99, a catch all, has a mask that intercepts all frames not intercepted by rule 1 or 2. Since the mask is 0x00000000, the filter will not be used since there no bits will pass the mask to be applied to the filter.
  Rule 99 will block the frame and not send anything to the other side.
  The modification bitmasks for the frame ID and data payload are unused for blocking rules.

In case no rule intercepts the frame, it will be forwarded to the other side unmodified.

CAN FRAME FORMAT