[PATCH bpf-next 6/6] selftests/bpf: add fixed vs rotating verifier log tests

[Andrii Nakryiko <andrii@kernel.org>]

Add selftests validating BPF_LOG_FIXED behavior, which used to be the
only behavior, and now default rotating BPF verifier log, which returns
just up to last N bytes of full verifier log, instead of returning
-ENOSPC.

To stress test correctness of in-kernel verifier log logic, we force it
to truncate program's verifier log to all lengths from 1 all the way to
its full size (about 450 bytes today). This was a useful stress test
while developing the feature.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 .../selftests/bpf/prog_tests/verifier_log.c   | 89 +++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/verifier_log.c

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier_log.c b/tools/testing/selftests/bpf/prog_tests/verifier_log.c
new file mode 100644
index 000000000000..4d9630d74ae0
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/verifier_log.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+
+#include "test_log_buf.skel.h"
+
+void test_verifier_log(void)
+{
+	LIBBPF_OPTS(bpf_prog_load_opts, opts);
+	char full_log[1024], log_buf[1024], *exp_log;
+	char prog_name[16], op_name[32];
+	struct test_log_buf *skel;
+	const struct bpf_insn *insns;
+	size_t insn_cnt, fixed_log_sz;
+	int i, err, prog_fd;
+
+	skel = test_log_buf__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	bpf_program__set_autoload(skel->progs.bad_prog, false);
+
+	err = test_log_buf__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	insns = bpf_program__insns(skel->progs.good_prog);
+	insn_cnt = bpf_program__insn_cnt(skel->progs.good_prog);
+
+	opts.log_buf = full_log;
+	opts.log_size = sizeof(full_log);
+	opts.log_level = 2 | 8 /* BPF_LOG_FIXED */;
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_RAW_TRACEPOINT, "log_fixed",
+				"GPL", insns, insn_cnt, &opts);
+	if (!ASSERT_GT(prog_fd, 0, "fixed_log_prog_load"))
+		goto cleanup;
+	close(prog_fd);
+
+	fixed_log_sz = strlen(full_log) + 1;
+	if (!ASSERT_GT(fixed_log_sz, 100, "fixed_log_sz"))
+		goto cleanup;
+
+	/* validate BPF_LOG_FIXED works as verifier log used to work, that is:
+	 * we get -ENOSPC and beginning of the full verifier log
+	 */
+	opts.log_buf = log_buf;
+	opts.log_level = 2 | 8; /* verbose level 2, fixed-length log */
+	opts.log_size = 50;
+
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_RAW_TRACEPOINT, "log_fixed50",
+				"GPL", insns, insn_cnt, &opts);
+	if (!ASSERT_EQ(prog_fd, -ENOSPC, "unexpected_log_fixed_prog_load_result")) {
+		if (prog_fd >= 0)
+			close(prog_fd);
+		goto cleanup;
+	}
+	if (!ASSERT_EQ(strlen(log_buf), 49, "log_fixed_50"))
+		goto cleanup;
+	if (!ASSERT_STRNEQ(log_buf, full_log, 49, op_name))
+		goto cleanup;
+
+	/* validate rolling verifier log logic: try all variations of log buf
+	 * length to force various truncation scenarios
+	 */
+	opts.log_buf = log_buf;
+	opts.log_level = 2; /* verbose level 2, rolling log */
+	for (i = 1; i <= fixed_log_sz; i++) {
+		opts.log_size = i;
+
+		snprintf(prog_name, sizeof(prog_name), "log_roll_%d", i);
+		prog_fd = bpf_prog_load(BPF_PROG_TYPE_RAW_TRACEPOINT, prog_name,
+					"GPL", insns, insn_cnt, &opts);
+
+		snprintf(op_name, sizeof(op_name), "log_roll_prog_load_%d", i);
+		if (!ASSERT_GT(prog_fd, 0, op_name))
+			goto cleanup;
+		close(prog_fd);
+
+		exp_log = full_log + fixed_log_sz - i;
+		snprintf(op_name, sizeof(op_name), "log_roll_contents_%d", i);
+		if (!ASSERT_STREQ(log_buf, exp_log, op_name))
+			goto cleanup;
+	}
+
+cleanup:
+	test_log_buf__destroy(skel);
+}
-- 
2.34.1