ebpf-lab

commit b184aa2dfa60f724fe717e97722744f7d6d25929
parent 81e3d302f2d322d60ed68ecbbc1e9bcd4538bc41
Author: Andreas Gruhler <andreas.gruhler@adfinis.com>
Date:   Sun, 14 May 2023 11:24:57 +0200

feat: add xdp networking example

Diffstat:
A
samples/xdp/Makefile
 | 
12
++++++++++++
A
samples/xdp/hello-xdp.bcc.c
 | 
70
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
samples/xdp/hello-xdp.bcc.o
 | 
0

3 files changed, 82 insertions(+), 0 deletions(-)
diff --git a/samples/xdp/Makefile b/samples/xdp/Makefile
@@ -0,0 +1,12 @@
+# Build BPF target:
+# * optimization level 2 required, unknown opcode 8d on bpftool prog load
+# otherwise
+# * include debugging symbols (-g) to pretty print map data with `pbftool map
+# dump`
+build:
+	clang \
+		-target bpf \
+		-O2 \
+		-g \
+		-o hello-xdp.bcc.o -c hello-xdp.bcc.c
+
diff --git a/samples/xdp/hello-xdp.bcc.c b/samples/xdp/hello-xdp.bcc.c
@@ -0,0 +1,70 @@
+#include <linux/bpf.h>
+// sections, printk, license, etc.
+#include <bpf/bpf_helpers.h>
+// bpf_ntohs
+#include <bpf/bpf_endian.h>
+// struct ethhdr
+#include <linux/if_ether.h>
+// struct iphdr
+#include <linux/ip.h>
+
+// https://github.com/lizrice/learning-ebpf/blob/main/chapter8
+
+// XDP type of BPF program
+SEC("xdp")
+
+int hello_xdp(struct xdp_md *ctx) {
+  // libpf version of BCCs bpf_trace_printk()
+  bpf_printk("received packet");
+  // XDP_PASS      : let the packet pass
+  // XDP_DROP      : you shall not pass
+  // XDP_TC        : send packet back through the interface it came through
+  // XDP_REDIRECT  : send packet to different interface
+
+  // Parse xdp packet and detect request type/protocol
+  int protocol = 0;
+
+  // pointers to start and end of packet in memory
+  void* data = (void*)(long)ctx->data;
+  void* data_end = (void*)(long)ctx->data_end;
+
+  // start of ethernet header
+  // /usr/include/linux/if_ether.h
+  // we could already lookup dest/source here
+  struct ethhdr* eth = data;
+
+  // check that packet is big enough for entire ethernet header
+  if (data + sizeof(struct ethhdr) > data_end)
+  // try to check this falsely and the verifiy will shout at you during bptool
+  // prog load (offset is outside of the packet)
+  //if (data + sizeof(struct ethhdr) <= data_end)
+    return XDP_DROP;
+
+  // check that it's an IP packet
+  // bpf_ntohs is a bpf helper
+  if (bpf_ntohs(eth->h_proto) != ETH_P_IP)
+    return XDP_DROP;
+
+  // start address of IP header
+  struct iphdr* iph = data + sizeof(struct ethhdr);
+
+  // check that entire header fits the packet
+  if (data + sizeof(struct ethhdr) + sizeof(struct iphdr) > data_end)
+    return XDP_DROP;
+
+  // fetch protocol type from IP header
+  // /usr/include/linux/ip.h
+  protocol = iph->protocol;
+
+  if (protocol == 1) {
+    // ICMP
+    bpf_printk("dropping ICMP packet");
+    return XDP_DROP;
+  }
+  return XDP_PASS;
+}
+
+// cannot call GPL-restricted functions (e.g., bpf_trace_printk) from non-GPL
+// compatible program
+char LICENSE[] SEC("license") = "GPL";
+
diff --git a/samples/xdp/hello-xdp.bcc.o b/samples/xdp/hello-xdp.bcc.o
Binary files differ.