Kernel: Start adding IPv4 support, starting with ICMP echo messages.

This doesn't work correctly yet, but it's getting nice enough to commit.

Kernel/ICMP.h

@@ -0,0 +1,51 @@
+#pragma once
+
+#include <Kernel/MACAddress.h>
+#include <Kernel/IPv4Packet.h>
+#include <Kernel/NetworkOrdered.h>
+
+struct ICMPType {
+enum {
+    EchoReply = 0,
+    EchoRequest = 8,
+};
+};
+
+class [[gnu::packed]] ICMPHeader {
+public:
+    ICMPHeader() { }
+    ~ICMPHeader() { }
+
+    byte type() const { return m_type; }
+    void set_type(byte b) { m_type = b; }
+
+    byte code() const { return m_code; }
+    void set_code(byte b) { m_code = b; }
+
+    word checksum() const { return ntohs(m_checksum); }
+    void set_checksum(word w) { m_checksum = htons(w); }
+
+    const void* payload() const { return &m_payload[0]; }
+    void* payload() { return &m_payload[0]; }
+
+private:
+    byte m_type { 0 };
+    byte m_code { 0 };
+    word m_checksum { 0 };
+    dword m_rest_of_header { 0 };
+    byte m_payload[0];
+};
+
+static_assert(sizeof(ICMPHeader) == 8);
+
+struct [[gnu::packed]] IPv4ICMPPacket {
+    IPv4Packet ipv4_packet;
+    ICMPHeader icmp_header;
+};
+
+struct [[gnu::packed]] ICMPEchoPacket {
+    ICMPHeader header;
+    NetworkOrdered<word> identifier;
+    NetworkOrdered<word> sequence_number;
+    byte payload[];
+};

Kernel/IPv4Packet.h

@@ -0,0 +1,58 @@
+#pragma once
+
+#include <AK/Types.h>
+#include <Kernel/IPv4Address.h>
+
+struct IPv4Protocol {
+enum {
+    ICMP = 1,
+};
+};
+
+class [[gnu::packed]] IPv4Packet {
+public:
+    byte version() const { return (m_version_and_ihl >> 4) & 0xf; }
+    void set_version(byte version) { m_version_and_ihl = (m_version_and_ihl & 0x0f) | (version << 4); }
+
+    byte internet_header_length() const { return m_version_and_ihl & 0xf; }
+    void set_internet_header_length(byte ihl) { m_version_and_ihl = (m_version_and_ihl & 0xf0) | (ihl & 0x0f); }
+
+    word length() const { return ntohs(m_length); }
+    void set_length(word length) { m_length = htons(length); }
+
+    word ident() const { return ntohs(m_ident); }
+    void set_ident(word ident) { m_ident = htons(ident); }
+
+    byte ttl() const { return m_ttl; }
+    void set_ttl(byte ttl) { m_ttl = ttl; }
+
+    byte protocol() const { return m_protocol; }
+    void set_protocol(byte protocol) { m_protocol = protocol; }
+
+    word checksum() const { return ntohs(m_checksum); }
+    void set_checksum(word checksum) { m_checksum = htons(checksum); }
+
+    const IPv4Address& source() const { return m_source; }
+    void set_source(const IPv4Address& address) { m_source = address; }
+
+    const IPv4Address& destination() const { return m_destination; }
+    void set_destination(const IPv4Address& address) { m_destination = address; }
+
+    void* payload() { return m_payload; }
+    const void* payload() const { return m_payload; }
+
+private:
+    byte m_version_and_ihl;
+    byte m_dscp_and_ecn;
+    word m_length;
+    word m_ident;
+    word m_flags_and_fragment;
+    byte m_ttl;
+    byte m_protocol;
+    word m_checksum;
+    IPv4Address m_source;
+    IPv4Address m_destination;
+    byte m_payload[0];
+};
+
+static_assert(sizeof(IPv4Packet) == 20);

Kernel/NetworkAdapter.cpp

@@ -24,6 +24,19 @@ void NetworkAdapter::send(const MACAddress& destination, const ARPPacket& packet
     kfree(eth);
 }
 
+void NetworkAdapter::send_ipv4(const MACAddress& destination, const void* packet, size_t packet_size)
+{
+    size_t size_in_bytes = sizeof(EthernetFrameHeader) + packet_size + sizeof(EthernetFrameCheckSequence);
+    auto* eth = (EthernetFrameHeader*)kmalloc(size_in_bytes);
+    eth->set_source(mac_address());
+    eth->set_destination(destination);
+    eth->set_ether_type(EtherType::IPv4);
+    memcpy(eth->payload(), packet, packet_size);
+    send_raw((byte*)eth, size_in_bytes);
+    kfree(eth);
+}
+
+
 void NetworkAdapter::did_receive(const byte* data, int length)
 {
     InterruptDisabler disabler;

Kernel/NetworkAdapter.h

@@ -6,6 +6,8 @@
 #include <Kernel/MACAddress.h>
 #include <Kernel/IPv4Address.h>
 #include <Kernel/ARPPacket.h>
+#include <Kernel/IPv4Packet.h>
+#include <Kernel/ICMP.h>
 
 class NetworkAdapter {
 public:
@@ -18,6 +20,7 @@ public:
     void set_ipv4_address(const IPv4Address&);
 
     void send(const MACAddress&, const ARPPacket&);
+    void send_ipv4(const MACAddress&, const void*, size_t);
 
     ByteBuffer dequeue_packet();
 

Kernel/NetworkOrdered.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <AK/Types.h>
+
+template<typename T>
+T convert_between_host_and_network(T host_value)
+{
+    if constexpr (sizeof(T) == 4) {
+        auto* s = (byte*)&host_value;
+        return (dword)(s[0] << 24 | s[1] << 16 | s[2] << 8 | s[3]);
+    }
+    if constexpr (sizeof(T) == 2) {
+        auto* s = (byte*)&host_value;
+        return (word)(s[0] << 8 | s[1]);
+    }
+    if constexpr (sizeof(T) == 1)
+        return host_value;
+}
+
+template<typename T>
+class [[gnu::packed]] NetworkOrdered {
+public:
+    NetworkOrdered()
+        : m_network_value(0)
+    {
+    }
+
+    NetworkOrdered(const T& host_value)
+        : m_network_value(convert_between_host_and_network(host_value))
+    {
+    }
+
+    NetworkOrdered(const NetworkOrdered& other)
+        : m_network_value(other.m_network_value)
+    {
+    }
+
+    NetworkOrdered& operator=(const NetworkOrdered& other)
+    {
+        m_network_value = other.m_network_value;
+        return *this;
+    }
+
+    operator T() const { return convert_between_host_and_network(m_network_value); }
+
+private:
+    T m_network_value;
+};

Kernel/NetworkTask.cpp

@@ -1,12 +1,18 @@
 #include <Kernel/E1000NetworkAdapter.h>
 #include <Kernel/EthernetFrameHeader.h>
 #include <Kernel/ARPPacket.h>
+#include <Kernel/ICMP.h>
+#include <Kernel/IPv4Packet.h>
 #include <Kernel/Process.h>
 #include <Kernel/EtherType.h>
 #include <AK/Lock.h>
 
+//#define ETHERNET_DEBUG
+//#define IPV4_DEBUG
+
 static void handle_arp(const EthernetFrameHeader&, int frame_size);
 static void handle_ipv4(const EthernetFrameHeader&, int frame_size);
+static void handle_icmp(const EthernetFrameHeader&, int frame_size);
 
 Lockable<HashMap<IPv4Address, MACAddress>>& arp_table()
 {
@@ -35,12 +41,14 @@ void NetworkTask_main()
             continue;
         }
         auto& eth = *(const EthernetFrameHeader*)packet.pointer();
+#ifdef ETHERNET_DEBUG
         kprintf("NetworkTask: From %s to %s, ether_type=%w, packet_length=%u\n",
             eth.source().to_string().characters(),
             eth.destination().to_string().characters(),
             eth.ether_type(),
             packet.size()
         );
+#endif
 
         switch (eth.ether_type()) {
         case EtherType::ARP:
@@ -123,5 +131,61 @@ void handle_arp(const EthernetFrameHeader& eth, int frame_size)
 
 void handle_ipv4(const EthernetFrameHeader& eth, int frame_size)
 {
-
+    constexpr int minimum_ipv4_frame_size = sizeof(EthernetFrameHeader) + sizeof(IPv4Packet) + sizeof(EthernetFrameCheckSequence);
+    if (frame_size < minimum_ipv4_frame_size) {
+        kprintf("handle_ipv4: Frame too small (%d, need %d)\n", frame_size, minimum_ipv4_frame_size);
+        return;
+    }
+    auto& packet = *static_cast<const IPv4Packet*>(eth.payload());
+
+#ifdef IPV4_DEBUG
+    kprintf("handle_ipv4: source=%s, target=%s\n",
+        packet.source().to_string().characters(),
+        packet.destination().to_string().characters()
+    );
+#endif
+
+    switch (packet.protocol()) {
+    case IPv4Protocol::ICMP:
+        return handle_icmp(eth, frame_size);
+    default:
+        kprintf("handle_ipv4: Unhandled protocol %u\n", packet.protocol());
+        break;
+    }
+}
+
+void handle_icmp(const EthernetFrameHeader& eth, int frame_size)
+{
+    auto& ipv4_packet = *static_cast<const IPv4Packet*>(eth.payload());
+    auto& icmp_header = *static_cast<const ICMPHeader*>(ipv4_packet.payload());
+    kprintf("handle_icmp: type=%b, code=%b\n", icmp_header.type(), icmp_header.code());
+
+    auto& e1000 = *E1000NetworkAdapter::the();
+    if (ipv4_packet.destination() == e1000.ipv4_address()) {
+        // It's for me!
+        if (icmp_header.type() == ICMPType::EchoRequest) {
+            auto& request = reinterpret_cast<const ICMPEchoPacket&>(icmp_header);
+            kprintf("ICMP echo request: id=%u, seq=%u\n", (int)request.identifier, (int)request.sequence_number);
+            byte* response_buffer = (byte*)kmalloc(ipv4_packet.length());
+            memset(response_buffer, 0, ipv4_packet.length());
+            struct [[gnu::packed]] EchoResponse {
+                IPv4Packet ipv4;
+                ICMPEchoPacket icmp_echo;
+            };
+            auto& response = *(EchoResponse*)response_buffer;
+            response.ipv4.set_version(4);
+            response.ipv4.set_internet_header_length(5);
+            response.ipv4.set_source(e1000.ipv4_address());
+            response.ipv4.set_destination(ipv4_packet.source());
+            response.ipv4.set_protocol(IPv4Protocol::ICMP);
+            response.ipv4.set_length(sizeof(IPv4ICMPPacket));
+            response.icmp_echo.header.set_type(ICMPType::EchoReply);
+            response.icmp_echo.header.set_code(0);
+            response.icmp_echo.identifier = request.identifier;
+            response.icmp_echo.sequence_number = request.sequence_number;
+            memcpy(response.icmp_echo.payload, request.payload, ipv4_packet.length() - sizeof(ICMPEchoPacket));
+            e1000.send_ipv4(eth.source(), &response, ipv4_packet.length());
+            kfree(response_buffer);
+        }
+    }
 }