selftests/bpf: Add test for libbpf's custom log_buf behavior

Add a selftest that validates that per-program and per-object log_buf
overrides work as expected. Also test same logic for low-level
bpf_prog_load() and bpf_btf_load() APIs.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211209193840.1248570-11-andrii@kernel.org

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+
+#include "test_log_buf.skel.h"
+
+static size_t libbpf_log_pos;
+static char libbpf_log_buf[1024 * 1024];
+static bool libbpf_log_error;
+
+static int libbpf_print_cb(enum libbpf_print_level level, const char *fmt, va_list args)
+{
+	int emitted_cnt;
+	size_t left_cnt;
+
+	left_cnt = sizeof(libbpf_log_buf) - libbpf_log_pos;
+	emitted_cnt = vsnprintf(libbpf_log_buf + libbpf_log_pos, left_cnt, fmt, args);
+
+	if (emitted_cnt < 0 || emitted_cnt + 1 > left_cnt) {
+		libbpf_log_error = true;
+		return 0;
+	}
+
+	libbpf_log_pos += emitted_cnt;
+	return 0;
+}
+
+static void obj_load_log_buf(void)
+{
+	libbpf_print_fn_t old_print_cb = libbpf_set_print(libbpf_print_cb);
+	LIBBPF_OPTS(bpf_object_open_opts, opts);
+	const size_t log_buf_sz = 1024 * 1024;
+	struct test_log_buf* skel;
+	char *obj_log_buf, *good_log_buf, *bad_log_buf;
+	int err;
+
+	obj_log_buf = malloc(3 * log_buf_sz);
+	if (!ASSERT_OK_PTR(obj_log_buf, "obj_log_buf"))
+		return;
+
+	good_log_buf = obj_log_buf + log_buf_sz;
+	bad_log_buf = obj_log_buf + 2 * log_buf_sz;
+	obj_log_buf[0] = good_log_buf[0] = bad_log_buf[0] = '\0';
+
+	opts.kernel_log_buf = obj_log_buf;
+	opts.kernel_log_size = log_buf_sz;
+	opts.kernel_log_level = 4; /* for BTF this will turn into 1 */
+
+	/* In the first round every prog has its own log_buf, so libbpf logs
+	 * don't have program failure logs
+	 */
+	skel = test_log_buf__open_opts(&opts);
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		goto cleanup;
+
+	/* set very verbose level for good_prog so we always get detailed logs */
+	bpf_program__set_log_buf(skel->progs.good_prog, good_log_buf, log_buf_sz);
+	bpf_program__set_log_level(skel->progs.good_prog, 2);
+
+	bpf_program__set_log_buf(skel->progs.bad_prog, bad_log_buf, log_buf_sz);
+	/* log_level 0 with custom log_buf means that verbose logs are not
+	 * requested if program load is successful, but libbpf should retry
+	 * with log_level 1 on error and put program's verbose load log into
+	 * custom log_buf
+	 */
+	bpf_program__set_log_level(skel->progs.bad_prog, 0);
+
+	err = test_log_buf__load(skel);
+	if (!ASSERT_ERR(err, "unexpected_load_success"))
+		goto cleanup;
+
+	ASSERT_FALSE(libbpf_log_error, "libbpf_log_error");
+
+	/* there should be no prog loading log because we specified per-prog log buf */
+	ASSERT_NULL(strstr(libbpf_log_buf, "-- BEGIN PROG LOAD LOG --"), "unexp_libbpf_log");
+	ASSERT_OK_PTR(strstr(libbpf_log_buf, "prog 'bad_prog': BPF program load failed"),
+		      "libbpf_log_not_empty");
+	ASSERT_OK_PTR(strstr(obj_log_buf, "DATASEC license"), "obj_log_not_empty");
+	ASSERT_OK_PTR(strstr(good_log_buf, "0: R1=ctx(id=0,off=0,imm=0) R10=fp0"),
+		      "good_log_verbose");
+	ASSERT_OK_PTR(strstr(bad_log_buf, "invalid access to map value, value_size=16 off=16000 size=4"),
+		      "bad_log_not_empty");
+
+	if (env.verbosity > VERBOSE_NONE) {
+		printf("LIBBPF LOG:   \n=================\n%s=================\n", libbpf_log_buf);
+		printf("OBJ LOG:      \n=================\n%s=================\n", obj_log_buf);
+		printf("GOOD_PROG LOG:\n=================\n%s=================\n", good_log_buf);
+		printf("BAD_PROG  LOG:\n=================\n%s=================\n", bad_log_buf);
+	}
+
+	/* reset everything */
+	test_log_buf__destroy(skel);
+	obj_log_buf[0] = good_log_buf[0] = bad_log_buf[0] = '\0';
+	libbpf_log_buf[0] = '\0';
+	libbpf_log_pos = 0;
+	libbpf_log_error = false;
+
+	/* In the second round we let bad_prog's failure be logged through print callback */
+	opts.kernel_log_buf = NULL; /* let everything through into print callback */
+	opts.kernel_log_size = 0;
+	opts.kernel_log_level = 1;
+
+	skel = test_log_buf__open_opts(&opts);
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		goto cleanup;
+
+	/* set normal verbose level for good_prog to check log_level is taken into account */
+	bpf_program__set_log_buf(skel->progs.good_prog, good_log_buf, log_buf_sz);
+	bpf_program__set_log_level(skel->progs.good_prog, 1);
+
+	err = test_log_buf__load(skel);
+	if (!ASSERT_ERR(err, "unexpected_load_success"))
+		goto cleanup;
+
+	ASSERT_FALSE(libbpf_log_error, "libbpf_log_error");
+
+	/* this time prog loading error should be logged through print callback */
+	ASSERT_OK_PTR(strstr(libbpf_log_buf, "libbpf: prog 'bad_prog': -- BEGIN PROG LOAD LOG --"),
+		      "libbpf_log_correct");
+	ASSERT_STREQ(obj_log_buf, "", "obj_log__empty");
+	ASSERT_STREQ(good_log_buf, "processed 4 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0\n",
+		     "good_log_ok");
+	ASSERT_STREQ(bad_log_buf, "", "bad_log_empty");
+
+	if (env.verbosity > VERBOSE_NONE) {
+		printf("LIBBPF LOG:   \n=================\n%s=================\n", libbpf_log_buf);
+		printf("OBJ LOG:      \n=================\n%s=================\n", obj_log_buf);
+		printf("GOOD_PROG LOG:\n=================\n%s=================\n", good_log_buf);
+		printf("BAD_PROG  LOG:\n=================\n%s=================\n", bad_log_buf);
+	}
+
+cleanup:
+	free(obj_log_buf);
+	test_log_buf__destroy(skel);
+	libbpf_set_print(old_print_cb);
+}
+
+static void bpf_prog_load_log_buf(void)
+{
+	const struct bpf_insn good_prog_insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	const size_t good_prog_insn_cnt = sizeof(good_prog_insns) / sizeof(struct bpf_insn);
+	const struct bpf_insn bad_prog_insns[] = {
+		BPF_EXIT_INSN(),
+	};
+	size_t bad_prog_insn_cnt = sizeof(bad_prog_insns) / sizeof(struct bpf_insn);
+	LIBBPF_OPTS(bpf_prog_load_opts, opts);
+	const size_t log_buf_sz = 1024 * 1024;
+	char *log_buf;
+	int fd = -1;
+
+	log_buf = malloc(log_buf_sz);
+	if (!ASSERT_OK_PTR(log_buf, "log_buf_alloc"))
+		return;
+	opts.log_buf = log_buf;
+	opts.log_size = log_buf_sz;
+
+	/* with log_level == 0 log_buf shoud stay empty for good prog */
+	log_buf[0] = '\0';
+	opts.log_level = 0;
+	fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "good_prog", "GPL",
+			   good_prog_insns, good_prog_insn_cnt, &opts);
+	ASSERT_STREQ(log_buf, "", "good_log_0");
+	ASSERT_GE(fd, 0, "good_fd1");
+	if (fd >= 0)
+		close(fd);
+	fd = -1;
+
+	/* log_level == 2 should always fill log_buf, even for good prog */
+	log_buf[0] = '\0';
+	opts.log_level = 2;
+	fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "good_prog", "GPL",
+			   good_prog_insns, good_prog_insn_cnt, &opts);
+	ASSERT_OK_PTR(strstr(log_buf, "0: R1=ctx(id=0,off=0,imm=0) R10=fp0"), "good_log_2");
+	ASSERT_GE(fd, 0, "good_fd2");
+	if (fd >= 0)
+		close(fd);
+	fd = -1;
+
+	/* log_level == 0 should fill log_buf for bad prog */
+	log_buf[0] = '\0';
+	opts.log_level = 0;
+	fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "bad_prog", "GPL",
+			   bad_prog_insns, bad_prog_insn_cnt, &opts);
+	ASSERT_OK_PTR(strstr(log_buf, "R0 !read_ok"), "bad_log_0");
+	ASSERT_LT(fd, 0, "bad_fd");
+	if (fd >= 0)
+		close(fd);
+	fd = -1;
+
+	free(log_buf);
+}
+
+static void bpf_btf_load_log_buf(void)
+{
+	LIBBPF_OPTS(bpf_btf_load_opts, opts);
+	const size_t log_buf_sz = 1024 * 1024;
+	const void *raw_btf_data;
+	__u32 raw_btf_size;
+	struct btf *btf;
+	char *log_buf;
+	int fd = -1;
+
+	btf = btf__new_empty();
+	if (!ASSERT_OK_PTR(btf, "empty_btf"))
+		return;
+
+	ASSERT_GT(btf__add_int(btf, "int", 4, 0), 0, "int_type");
+
+	raw_btf_data = btf__raw_data(btf, &raw_btf_size);
+	if (!ASSERT_OK_PTR(raw_btf_data, "raw_btf_data_good"))
+		goto cleanup;
+
+	log_buf = malloc(log_buf_sz);
+	if (!ASSERT_OK_PTR(log_buf, "log_buf_alloc"))
+		goto cleanup;
+	opts.log_buf = log_buf;
+	opts.log_size = log_buf_sz;
+
+	/* with log_level == 0 log_buf shoud stay empty for good BTF */
+	log_buf[0] = '\0';
+	opts.log_level = 0;
+	fd = bpf_btf_load(raw_btf_data, raw_btf_size, &opts);
+	ASSERT_STREQ(log_buf, "", "good_log_0");
+	ASSERT_GE(fd, 0, "good_fd1");
+	if (fd >= 0)
+		close(fd);
+	fd = -1;
+
+	/* log_level == 2 should always fill log_buf, even for good BTF */
+	log_buf[0] = '\0';
+	opts.log_level = 2;
+	fd = bpf_btf_load(raw_btf_data, raw_btf_size, &opts);
+	printf("LOG_BUF: %s\n", log_buf);
+	ASSERT_OK_PTR(strstr(log_buf, "magic: 0xeb9f"), "good_log_2");
+	ASSERT_GE(fd, 0, "good_fd2");
+	if (fd >= 0)
+		close(fd);
+	fd = -1;
+
+	/* make BTF bad, add pointer pointing to non-existing type */
+	ASSERT_GT(btf__add_ptr(btf, 100), 0, "bad_ptr_type");
+
+	raw_btf_data = btf__raw_data(btf, &raw_btf_size);
+	if (!ASSERT_OK_PTR(raw_btf_data, "raw_btf_data_bad"))
+		goto cleanup;
+
+	/* log_level == 0 should fill log_buf for bad BTF */
+	log_buf[0] = '\0';
+	opts.log_level = 0;
+	fd = bpf_btf_load(raw_btf_data, raw_btf_size, &opts);
+	printf("LOG_BUF: %s\n", log_buf);
+	ASSERT_OK_PTR(strstr(log_buf, "[2] PTR (anon) type_id=100 Invalid type_id"), "bad_log_0");
+	ASSERT_LT(fd, 0, "bad_fd");
+	if (fd >= 0)
+		close(fd);
+	fd = -1;
+
+cleanup:
+	free(log_buf);
+	btf__free(btf);
+}
+
+void test_log_buf(void)
+{
+	if (test__start_subtest("obj_load_log_buf"))
+		obj_load_log_buf();
+	if (test__start_subtest("bpf_prog_load_log_buf"))
+		bpf_prog_load_log_buf();
+	if (test__start_subtest("bpf_btf_load_log_buf"))
+		bpf_btf_load_log_buf();
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+int a[4];
+const volatile int off = 4000;
+
+SEC("raw_tp/sys_enter")
+int good_prog(const void *ctx)
+{
+	a[0] = (int)(long)ctx;
+	return a[1];
+}
+
+SEC("raw_tp/sys_enter")
+int bad_prog(const void *ctx)
+{
+	/* out of bounds access */
+	return a[off];
+}
+
+char _license[] SEC("license") = "GPL";