selftests/bpf: Add tests to validate log_true_size feature

Add additional test cases validating that log_true_size is consistent
between fixed and rotating log modes, and that log_true_size can be
used *exactly* without causing -ENOSPC, while using just 1 byte shorter
log buffer would cause -ENOSPC.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Lorenz Bauer <lmb@isovalent.com>
Link: https://lore.kernel.org/bpf/20230406234205.323208-18-andrii@kernel.org

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

@@ -18,25 +18,41 @@ static bool check_prog_load(int prog_fd, bool expect_err, const char *tag)
 		if (!ASSERT_GT(prog_fd, 0, tag))
 			return false;
 	}
+	if (prog_fd >= 0)
+		close(prog_fd);
 	return true;
 }
 
+static 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;
+static const struct bpf_insn *insns;
+static size_t insn_cnt;
+
+static int load_prog(struct bpf_prog_load_opts *opts, bool expect_load_error)
+{
+	int prog_fd;
+
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_RAW_TRACEPOINT, "log_prog",
+				"GPL", insns, insn_cnt, opts);
+	check_prog_load(prog_fd, expect_load_error, "prog_load");
+
+	return prog_fd;
+}
+
 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, mode, err, prog_fd;
+	size_t fixed_log_sz;
+	__u32 log_true_sz_fixed, log_true_sz_rolling;
+	int i, mode, err, prog_fd, res;
 
 	skel = test_log_buf__open();
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
@@ -61,11 +77,7 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_
 	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);
+	load_prog(&opts, expect_load_error);
 
 	fixed_log_sz = strlen(logs.reference) + 1;
 	if (!ASSERT_GT(fixed_log_sz, 50, "fixed_log_sz"))
@@ -89,7 +101,7 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_
 		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",
+		prog_fd = bpf_prog_load(BPF_PROG_TYPE_RAW_TRACEPOINT, "log_fixed25",
 					"GPL", insns, insn_cnt, &opts);
 		if (!ASSERT_EQ(prog_fd, -ENOSPC, "unexpected_log_fixed_prog_load_result")) {
 			if (prog_fd >= 0)
@@ -162,6 +174,54 @@ static void verif_log_subtest(const char *name, bool expect_load_error, int log_
 		}
 	}
 
+	/* (FIXED) get actual log size */
+	opts.log_buf = logs.buf;
+	opts.log_level = log_level | 8; /* BPF_LOG_FIXED */
+	opts.log_size = sizeof(logs.buf);
+	res = load_prog(&opts, expect_load_error);
+	ASSERT_NEQ(res, -ENOSPC, "prog_load_res_fixed");
+
+	log_true_sz_fixed = opts.log_true_size;
+	ASSERT_GT(log_true_sz_fixed, 0, "log_true_sz_fixed");
+
+	/* (ROLLING) get actual log size */
+	opts.log_buf = logs.buf;
+	opts.log_level = log_level;
+	opts.log_size = sizeof(logs.buf);
+	res = load_prog(&opts, expect_load_error);
+	ASSERT_NEQ(res, -ENOSPC, "prog_load_res_rolling");
+
+	log_true_sz_rolling = opts.log_true_size;
+	ASSERT_EQ(log_true_sz_rolling, log_true_sz_fixed, "log_true_sz_eq");
+
+	/* (FIXED) expect -ENOSPC for one byte short log */
+	opts.log_buf = logs.buf;
+	opts.log_level = log_level | 8; /* BPF_LOG_FIXED */
+	opts.log_size = log_true_sz_fixed - 1;
+	res = load_prog(&opts, true /* should fail */);
+	ASSERT_EQ(res, -ENOSPC, "prog_load_res_too_short_fixed");
+
+	/* (FIXED) expect *not* -ENOSPC with exact log_true_size buffer */
+	opts.log_buf = logs.buf;
+	opts.log_level = log_level | 8; /* BPF_LOG_FIXED */
+	opts.log_size = log_true_sz_fixed;
+	res = load_prog(&opts, expect_load_error);
+	ASSERT_NEQ(res, -ENOSPC, "prog_load_res_just_right_fixed");
+
+	/* (ROLLING) expect -ENOSPC for one byte short log */
+	opts.log_buf = logs.buf;
+	opts.log_level = log_level;
+	opts.log_size = log_true_sz_rolling - 1;
+	res = load_prog(&opts, true /* should fail */);
+	ASSERT_EQ(res, -ENOSPC, "prog_load_res_too_short_rolling");
+
+	/* (ROLLING) expect *not* -ENOSPC with exact log_true_size buffer */
+	opts.log_buf = logs.buf;
+	opts.log_level = log_level;
+	opts.log_size = log_true_sz_rolling;
+	res = load_prog(&opts, expect_load_error);
+	ASSERT_NEQ(res, -ENOSPC, "prog_load_res_just_right_rolling");
+
 cleanup:
 	test_log_buf__destroy(skel);
 }