[PATCH v2 bpf-next 6/6] selftests/bpf: add fixed vs rotating verifier log tests

Andrii Nakryiko
2023-03-28T23:57:17Z

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.

For both fixed and rotating log modes we expect -ENOSPC if log contents
doesn't fit in user-supplied log buffer.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
.../selftests/bpf/prog_tests/verifier_log.c | 164 ++++++++++++++++++
1 file changed, 164 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..afe9e0384055
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/verifier_log.c
@@ -0,0 +1,164 @@
+// 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"
+
+
+static bool check_prog_load(int prog_fd, bool expect_err, const char *tag)
+{
+ if (expect_err) {
+ if (!ASSERT_LT(prog_fd, 0, tag)) {
+ close(prog_fd);
+ return false;
+ }
+ } else /* !expect_err */ {
+ if (!ASSERT_GT(prog_fd, 0, tag))
+ return false;
+ }
+ return true;
+}
+
+static void verif_log_subtest(const char *name, bool expect_load_error, int log_level)
+{
+ LIBBPF_OPTS(bpf_prog_load_opts, opts);
+ struct {
+ /* strategically placed before others to avoid accidental modification by kernel */
+ char filler[1024];
+ char buf[1024];
+ /* strategically placed after buf[] to catch more accidental corruptions */
+ char reference[1024];
+ } logs;
+ char *exp_log, prog_name[16], op_name[32];
+ struct test_log_buf *skel;
+ struct bpf_program *prog;
+ 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_object__for_each_program(prog, skel->obj) {
+ if (strcmp(bpf_program__name(prog), name) == 0)
+ bpf_program__set_autoload(prog, true);
+ else
+ bpf_program__set_autoload(prog, false);
+ }
+
+ err = test_log_buf__load(skel);
+ if (!expect_load_error && !ASSERT_OK(err, "unexpected_load_failure"))
+ goto cleanup;
+ if (expect_load_error && !ASSERT_ERR(err, "unexpected_load_success"))
+ goto cleanup;
+
+ insns = bpf_program__insns(skel->progs.good_prog);
+ insn_cnt = bpf_program__insn_cnt(skel->progs.good_prog);
+
+ opts.log_buf = logs.reference;
+ opts.log_size = sizeof(logs.reference);
+ opts.log_level = log_level | 8 /* BPF_LOG_FIXED */;
+ prog_fd = bpf_prog_load(BPF_PROG_TYPE_RAW_TRACEPOINT, "log_fixed",
+ "GPL", insns, insn_cnt, &opts);
+ if (!check_prog_load(prog_fd, expect_load_error, "fixed_buf_prog_load"))
+ goto cleanup;
+ close(prog_fd);
+
+ fixed_log_sz = strlen(logs.reference) + 1;
+ if (!ASSERT_GT(fixed_log_sz, 50, "fixed_log_sz"))
+ goto cleanup;
+ memset(logs.reference + fixed_log_sz, 0, sizeof(logs.reference) - fixed_log_sz);
+
+ /* validate BPF_LOG_FIXED works as verifier log used to work, that is:
+ * we get -ENOSPC and beginning of the full verifier log. This only
+ * works for log_level 2 and log_level 1 + failed program. For log
+ * level 2 we don't reset log at all. For log_level 1 + failed program
+ * we don't get to verification stats output. With log level 1
+ * for successful program final result will be just verifier stats.
+ * But if provided too short log buf, kernel will NULL-out log->ubuf
+ * and will stop emitting further log. This means we'll never see
+ * predictable verifier stats.
+ * Long story short, we do the following -ENOSPC test only for
+ * predictable combinations.
+ */
+ if (log_level >= 2 || expect_load_error) {
+ opts.log_buf = logs.buf;
+ opts.log_level = log_level | 8; /* fixed-length log */
+ opts.log_size = 25;
+
+ 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(logs.buf), 24, "log_fixed_25"))
+ goto cleanup;
+ if (!ASSERT_STRNEQ(logs.buf, logs.reference, 24, op_name))
+ goto cleanup;
+ }
+
+ /* validate rolling verifier log logic: try all variations of log buf
+ * length to force various truncation scenarios
+ */
+ opts.log_buf = logs.buf;
+ opts.log_level = log_level; /* rolling log */
+
+ /* prefill logs.buf with 'A's to detect any write beyond allowed length */
+ memset(logs.filler, 'A', sizeof(logs.filler));
+ logs.filler[sizeof(logs.filler) - 1] = '\0';
+ memset(logs.buf, 'A', sizeof(logs.buf));
+ logs.buf[sizeof(logs.buf) - 1] = '\0';
+
+ 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_EQ(prog_fd, -ENOSPC, op_name)) {
+ if (prog_fd >= 0)
+ close(prog_fd);
+ goto cleanup;
+ }
+
+ exp_log = logs.reference + fixed_log_sz - i;
+ snprintf(op_name, sizeof(op_name), "log_roll_contents_%d", i);
+ if (!ASSERT_STREQ(logs.buf, exp_log, op_name)) {
+ printf("CMP:%d\nS1:'%s'\nS2:'%s'\n",
+ strcmp(logs.buf, exp_log),
+ logs.buf, exp_log);
+ goto cleanup;
+ }
+
+ /* check that unused portions of logs.buf is not overwritten */
+ snprintf(op_name, sizeof(op_name), "log_roll_unused_tail_%d", i);
+ if (!ASSERT_STREQ(logs.buf + i, logs.filler + i, op_name)) {
+ printf("CMP:%d\nS1:'%s'\nS2:'%s'\n",
+ strcmp(logs.buf + i, logs.filler + i),
+ logs.buf + i, logs.filler + i);
+ goto cleanup;
+ }
+ }
+
+cleanup:
+ test_log_buf__destroy(skel);
+}
+
+void test_verifier_log(void)
+{
+ if (test__start_subtest("good_prog-level1"))
+ verif_log_subtest("good_prog", false, 1);
+ if (test__start_subtest("good_prog-level2"))
+ verif_log_subtest("good_prog", false, 2);
+ if (test__start_subtest("bad_prog-level1"))
+ verif_log_subtest("bad_prog", true, 1);
+ if (test__start_subtest("bad_prog-level2"))
+ verif_log_subtest("bad_prog", true, 2);
+}
--
2.34.1