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 <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: John Fastabend <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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";