selftests/bpf: Add skb_pkt_end test

Add a test that currently makes LLVM generate assembly code:

$ llvm-objdump -S skb_pkt_end.o
0000000000000000 <main_prog>:
; 	if (skb_shorter(skb, ETH_IPV4_TCP_SIZE))
       0:	61 12 50 00 00 00 00 00	r2 = *(u32 *)(r1 + 80)
       1:	61 14 4c 00 00 00 00 00	r4 = *(u32 *)(r1 + 76)
       2:	bf 43 00 00 00 00 00 00	r3 = r4
       3:	07 03 00 00 36 00 00 00	r3 += 54
       4:	b7 01 00 00 00 00 00 00	r1 = 0
       5:	2d 23 02 00 00 00 00 00	if r3 > r2 goto +2 <LBB0_2>
       6:	07 04 00 00 0e 00 00 00	r4 += 14
; 	if (skb_shorter(skb, ETH_IPV4_TCP_SIZE))
       7:	bf 41 00 00 00 00 00 00	r1 = r4
0000000000000040 <LBB0_2>:
       8:	b4 00 00 00 ff ff ff ff	w0 = -1
; 	if (!(ip = get_iphdr(skb)))
       9:	2d 23 05 00 00 00 00 00	if r3 > r2 goto +5 <LBB0_6>
; 	proto = ip->protocol;
      10:	71 12 09 00 00 00 00 00	r2 = *(u8 *)(r1 + 9)
; 	if (proto != IPPROTO_TCP)
      11:	56 02 03 00 06 00 00 00	if w2 != 6 goto +3 <LBB0_6>
; 	if (tcp->dest != 0)
      12:	69 12 16 00 00 00 00 00	r2 = *(u16 *)(r1 + 22)
      13:	56 02 01 00 00 00 00 00	if w2 != 0 goto +1 <LBB0_6>
; 	return tcp->urg_ptr;
      14:	69 10 26 00 00 00 00 00	r0 = *(u16 *)(r1 + 38)
0000000000000078 <LBB0_6>:
; }
      15:	95 00 00 00 00 00 00 00	exit
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20201111031213.25109-3-alexei.starovoitov@gmail.com

tools/testing/selftests/bpf/prog_tests/test_skb_pkt_end.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "skb_pkt_end.skel.h"
+
+static int sanity_run(struct bpf_program *prog)
+{
+	__u32 duration, retval;
+	int err, prog_fd;
+
+	prog_fd = bpf_program__fd(prog);
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, &retval, &duration);
+	if (CHECK(err || retval != 123, "test_run",
+		  "err %d errno %d retval %d duration %d\n",
+		  err, errno, retval, duration))
+		return -1;
+	return 0;
+}
+
+void test_test_skb_pkt_end(void)
+{
+	struct skb_pkt_end *skb_pkt_end_skel = NULL;
+	__u32 duration = 0;
+	int err;
+
+	skb_pkt_end_skel = skb_pkt_end__open_and_load();
+	if (CHECK(!skb_pkt_end_skel, "skb_pkt_end_skel_load", "skb_pkt_end skeleton failed\n"))
+		goto cleanup;
+
+	err = skb_pkt_end__attach(skb_pkt_end_skel);
+	if (CHECK(err, "skb_pkt_end_attach", "skb_pkt_end attach failed: %d\n", err))
+		goto cleanup;
+
+	if (sanity_run(skb_pkt_end_skel->progs.main_prog))
+		goto cleanup;
+
+cleanup:
+	skb_pkt_end__destroy(skb_pkt_end_skel);
+}

tools/testing/selftests/bpf/progs/skb_pkt_end.c

+// SPDX-License-Identifier: GPL-2.0
+#define BPF_NO_PRESERVE_ACCESS_INDEX
+#include <vmlinux.h>
+#include <bpf/bpf_core_read.h>
+#include <bpf/bpf_helpers.h>
+
+#define NULL 0
+#define INLINE __always_inline
+
+#define skb_shorter(skb, len) ((void *)(long)(skb)->data + (len) > (void *)(long)skb->data_end)
+
+#define ETH_IPV4_TCP_SIZE (14 + sizeof(struct iphdr) + sizeof(struct tcphdr))
+
+static INLINE struct iphdr *get_iphdr(struct __sk_buff *skb)
+{
+	struct iphdr *ip = NULL;
+	struct ethhdr *eth;
+
+	if (skb_shorter(skb, ETH_IPV4_TCP_SIZE))
+		goto out;
+
+	eth = (void *)(long)skb->data;
+	ip = (void *)(eth + 1);
+
+out:
+	return ip;
+}
+
+SEC("classifier/cls")
+int main_prog(struct __sk_buff *skb)
+{
+	struct iphdr *ip = NULL;
+	struct tcphdr *tcp;
+	__u8 proto = 0;
+
+	if (!(ip = get_iphdr(skb)))
+		goto out;
+
+	proto = ip->protocol;
+
+	if (proto != IPPROTO_TCP)
+		goto out;
+
+	tcp = (void*)(ip + 1);
+	if (tcp->dest != 0)
+		goto out;
+	if (!tcp)
+		goto out;
+
+	return tcp->urg_ptr;
+out:
+	return -1;
+}
+char _license[] SEC("license") = "GPL";