selftests/bpf: Adding test for arg dereference in extension trace

Adding test that setup following program:

  SEC("classifier/test_pkt_md_access")
  int test_pkt_md_access(struct __sk_buff *skb)

with its extension:

  SEC("freplace/test_pkt_md_access")
  int test_pkt_md_access_new(struct __sk_buff *skb)

and tracing that extension with:

  SEC("fentry/test_pkt_md_access_new")
  int BPF_PROG(fentry, struct sk_buff *skb)

The test verifies that the tracing program can
dereference skb argument properly.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/160138355603.48470.9072073357530773228.stgit@toke.dk

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

+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <test_progs.h>
+#include <network_helpers.h>
+#include <sys/stat.h>
+#include <linux/sched.h>
+#include <sys/syscall.h>
+
+#include "test_pkt_md_access.skel.h"
+#include "test_trace_ext.skel.h"
+#include "test_trace_ext_tracing.skel.h"
+
+static __u32 duration;
+
+void test_trace_ext(void)
+{
+	struct test_pkt_md_access *skel_pkt = NULL;
+	struct test_trace_ext_tracing *skel_trace = NULL;
+	struct test_trace_ext_tracing__bss *bss_trace;
+	struct test_trace_ext *skel_ext = NULL;
+	struct test_trace_ext__bss *bss_ext;
+	int err, pkt_fd, ext_fd;
+	struct bpf_program *prog;
+	char buf[100];
+	__u32 retval;
+	__u64 len;
+
+	/* open/load/attach test_pkt_md_access */
+	skel_pkt = test_pkt_md_access__open_and_load();
+	if (CHECK(!skel_pkt, "setup", "classifier/test_pkt_md_access open failed\n"))
+		goto cleanup;
+
+	err = test_pkt_md_access__attach(skel_pkt);
+	if (CHECK(err, "setup", "classifier/test_pkt_md_access attach failed: %d\n", err))
+		goto cleanup;
+
+	prog = skel_pkt->progs.test_pkt_md_access;
+	pkt_fd = bpf_program__fd(prog);
+
+	/* open extension */
+	skel_ext = test_trace_ext__open();
+	if (CHECK(!skel_ext, "setup", "freplace/test_pkt_md_access open failed\n"))
+		goto cleanup;
+
+	/* set extension's attach target - test_pkt_md_access  */
+	prog = skel_ext->progs.test_pkt_md_access_new;
+	bpf_program__set_attach_target(prog, pkt_fd, "test_pkt_md_access");
+
+	/* load/attach extension */
+	err = test_trace_ext__load(skel_ext);
+	if (CHECK(err, "setup", "freplace/test_pkt_md_access load failed\n")) {
+		libbpf_strerror(err, buf, sizeof(buf));
+		fprintf(stderr, "%s\n", buf);
+		goto cleanup;
+	}
+
+	err = test_trace_ext__attach(skel_ext);
+	if (CHECK(err, "setup", "freplace/test_pkt_md_access attach failed: %d\n", err))
+		goto cleanup;
+
+	prog = skel_ext->progs.test_pkt_md_access_new;
+	ext_fd = bpf_program__fd(prog);
+
+	/* open tracing  */
+	skel_trace = test_trace_ext_tracing__open();
+	if (CHECK(!skel_trace, "setup", "tracing/test_pkt_md_access_new open failed\n"))
+		goto cleanup;
+
+	/* set tracing's attach target - fentry */
+	prog = skel_trace->progs.fentry;
+	bpf_program__set_attach_target(prog, ext_fd, "test_pkt_md_access_new");
+
+	/* set tracing's attach target - fexit */
+	prog = skel_trace->progs.fexit;
+	bpf_program__set_attach_target(prog, ext_fd, "test_pkt_md_access_new");
+
+	/* load/attach tracing */
+	err = test_trace_ext_tracing__load(skel_trace);
+	if (CHECK(err, "setup", "tracing/test_pkt_md_access_new load failed\n")) {
+		libbpf_strerror(err, buf, sizeof(buf));
+		fprintf(stderr, "%s\n", buf);
+		goto cleanup;
+	}
+
+	err = test_trace_ext_tracing__attach(skel_trace);
+	if (CHECK(err, "setup", "tracing/test_pkt_md_access_new attach failed: %d\n", err))
+		goto cleanup;
+
+	/* trigger the test */
+	err = bpf_prog_test_run(pkt_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, &retval, &duration);
+	CHECK(err || retval, "run", "err %d errno %d retval %d\n", err, errno, retval);
+
+	bss_ext = skel_ext->bss;
+	bss_trace = skel_trace->bss;
+
+	len = bss_ext->ext_called;
+
+	CHECK(bss_ext->ext_called == 0,
+		"check", "failed to trigger freplace/test_pkt_md_access\n");
+	CHECK(bss_trace->fentry_called != len,
+		"check", "failed to trigger fentry/test_pkt_md_access_new\n");
+	CHECK(bss_trace->fexit_called != len,
+		"check", "failed to trigger fexit/test_pkt_md_access_new\n");
+
+cleanup:
+	test_trace_ext_tracing__destroy(skel_trace);
+	test_trace_ext__destroy(skel_ext);
+	test_pkt_md_access__destroy(skel_pkt);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+#include <linux/bpf.h>
+#include <stdbool.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+#include <bpf/bpf_tracing.h>
+
+__u64 ext_called = 0;
+
+SEC("freplace/test_pkt_md_access")
+int test_pkt_md_access_new(struct __sk_buff *skb)
+{
+	ext_called = skb->len;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

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

+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+__u64 fentry_called = 0;
+
+SEC("fentry/test_pkt_md_access_new")
+int BPF_PROG(fentry, struct sk_buff *skb)
+{
+	fentry_called = skb->len;
+	return 0;
+}
+
+__u64 fexit_called = 0;
+
+SEC("fexit/test_pkt_md_access_new")
+int BPF_PROG(fexit, struct sk_buff *skb)
+{
+	fexit_called = skb->len;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";