[bpf-next,v3,2/3] selftests/bpf: Add test for recursive attachment of tracing progs

Commit Message

Dmitry Dolgov Nov. 29, 2023, 7:16 p.m. UTC

Verify the fact that an fentry prog could be attached to another one,
building up an attachment chain of limited size. Use existing
bpf_testmod as a start of the chain.

Note, that currently it's not possible to:
* form a cycle within an attachment chain
* splice two attachment chains

Those limitations are coming from the fact that attach_prog_fd is
specified at the prog load (thus making it impossible to attach to a
program loaded after it in this way), as well as tracing progs not
implementing link_detach. This is the reason there is only one test for
the chain length.

Signed-off-by: Dmitrii Dolgov <[e-mail]>
---
 .../bpf/prog_tests/recursive_attach.c         | 85 +++++++++++++++++++
 .../selftests/bpf/progs/fentry_recursive.c    | 19 +++++
 .../bpf/progs/fentry_recursive_target.c       | 20 +++++
 3 files changed, 124 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/recursive_attach.c
 create mode 100644 tools/testing/selftests/bpf/progs/fentry_recursive.c
 create mode 100644 tools/testing/selftests/bpf/progs/fentry_recursive_target.c

Patch

diff --git a/tools/testing/selftests/bpf/prog_tests/recursive_attach.c b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c
new file mode 100644
index 000000000000..9c422dd92c4e
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c
@@ -0,0 +1,85 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Red Hat, Inc. */
+#include <test_progs.h>
+#include "fentry_recursive.skel.h"
+#include "fentry_recursive_target.skel.h"
+#include <bpf/btf.h>
+#include "bpf/libbpf_internal.h"
+
+#define ATTACH_DEPTH 33
+
+/*
+ * Test following scenarios:
+ * - one can attach fentry progs recursively, one fentry to another one
+ * - an attachment chain generated this way is limited, after 32 attachment no
+ *   more progs could be added
+ */
+void test_recursive_fentry_attach(void)
+{
+	struct fentry_recursive_target *target_skel = NULL;
+	struct fentry_recursive *tracing_chain[ATTACH_DEPTH + 1] = {};
+	struct bpf_program *prog;
+	int prev_fd, err;
+
+	target_skel = fentry_recursive_target__open_and_load();
+	if (!ASSERT_OK_PTR(target_skel, "fentry_recursive_target__open_and_load"))
+		goto close_prog;
+
+	/* This is going to be the start of the chain */
+	tracing_chain[0] = fentry_recursive__open();
+	if (!ASSERT_OK_PTR(tracing_chain[0], "fentry_recursive__open"))
+		goto close_prog;
+
+	prog = tracing_chain[0]->progs.recursive_attach;
+	prev_fd = bpf_program__fd(target_skel->progs.test1);
+	err = bpf_program__set_attach_target(prog, prev_fd, "test1");
+	if (!ASSERT_OK(err, "bpf_program__set_attach_target"))
+		goto close_prog;
+
+	err = fentry_recursive__load(tracing_chain[0]);
+	if (!ASSERT_OK(err, "fentry_recursive__load"))
+		goto close_prog;
+
+	/* Create an attachment chain to exhaust the limit */
+	for (int i = 1; i < ATTACH_DEPTH; i++) {
+		tracing_chain[i] = fentry_recursive__open();
+		if (!ASSERT_OK_PTR(tracing_chain[i], "fentry_recursive__open"))
+			goto close_prog;
+
+		prog = tracing_chain[i]->progs.recursive_attach;
+		prev_fd = bpf_program__fd(tracing_chain[i-1]->progs.recursive_attach);
+		err = bpf_program__set_attach_target(prog, prev_fd, "recursive_attach");
+		if (!ASSERT_OK(err, "bpf_program__set_attach_target"))
+			goto close_prog;
+
+		err = fentry_recursive__load(tracing_chain[i]);
+		if (!ASSERT_OK(err, "fentry_recursive__load"))
+			goto close_prog;
+
+		err = fentry_recursive__attach(tracing_chain[i]);
+		if (!ASSERT_OK(err, "fentry_recursive__attach"))
+			goto close_prog;
+	}
+
+	/* The next attachment would fail */
+	tracing_chain[ATTACH_DEPTH] = fentry_recursive__open();
+	if (!ASSERT_OK_PTR(tracing_chain[ATTACH_DEPTH], "last fentry_recursive__open"))
+		goto close_prog;
+
+	prog = tracing_chain[ATTACH_DEPTH]->progs.recursive_attach;
+	prev_fd = bpf_program__fd(tracing_chain[ATTACH_DEPTH - 1]->progs.recursive_attach);
+	err = bpf_program__set_attach_target(prog, prev_fd, "recursive_attach");
+	if (!ASSERT_OK(err, "last bpf_program__set_attach_target"))
+		goto close_prog;
+
+	err = fentry_recursive__load(tracing_chain[ATTACH_DEPTH]);
+	if (!ASSERT_ERR(err, "last fentry_recursive__load"))
+		goto close_prog;
+
+close_prog:
+	fentry_recursive_target__destroy(target_skel);
+	for (int i = 1; i < ATTACH_DEPTH + 1; i++) {
+		if (tracing_chain[i])
+			fentry_recursive__destroy(tracing_chain[i]);
+	}
+}
diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive.c b/tools/testing/selftests/bpf/progs/fentry_recursive.c
new file mode 100644
index 000000000000..1df490230344
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/fentry_recursive.c
@@ -0,0 +1,19 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Red Hat, Inc. */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u64 test1_result = 0;
+
+/*
+ * Dummy fentry bpf prog for testing fentry attachment chains
+ */
+SEC("fentry/XXX")
+int BPF_PROG(recursive_attach, int a)
+{
+	test1_result = a == 1;
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive_target.c b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c
new file mode 100644
index 000000000000..b6fb8ebd598d
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c
@@ -0,0 +1,20 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Red Hat, Inc. */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u64 test1_result = 0;
+
+/*
+ * Dummy fentry bpf prog for testing fentry attachment chains. It's going to be
+ * a start of the chain.
+ */
+SEC("fentry/bpf_testmod_fentry_test1")
+int BPF_PROG(test1, int a)
+{
+	test1_result = a == 1;
+	return 0;
+}