selftests/bpf: test for malformed BPF_CORE_TYPE_ID_LOCAL relocation

Check that verifier rejects BPF program containing relocation
pointing to non-existent BTF type.

To force relocation resolution on kernel side test case uses
bpf_attr->core_relos field. This field is not exposed by libbpf,
so directly do BPF system call in the test.

Signed-off-by: Eduard Zingerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
+// SPDX-License-Identifier: GPL-2.0
+
+/* Test cases that can't load programs using libbpf and need direct
+ * BPF syscall access
+ */
+
+#include <sys/syscall.h>
+#include <bpf/libbpf.h>
+#include <bpf/btf.h>
+
+#include "test_progs.h"
+#include "test_btf.h"
+#include "bpf/libbpf_internal.h"
+
+static char log[16 * 1024];
+
+/* Check that verifier rejects BPF program containing relocation
+ * pointing to non-existent BTF type.
+ */
+static void test_bad_local_id(void)
+{
+	struct test_btf {
+		struct btf_header hdr;
+		__u32 types[15];
+		char strings[128];
+	} raw_btf = {
+		.hdr = {
+			.magic = BTF_MAGIC,
+			.version = BTF_VERSION,
+			.hdr_len = sizeof(struct btf_header),
+			.type_off = 0,
+			.type_len = sizeof(raw_btf.types),
+			.str_off = offsetof(struct test_btf, strings) -
+				   offsetof(struct test_btf, types),
+			.str_len = sizeof(raw_btf.strings),
+		},
+		.types = {
+			BTF_PTR_ENC(0),					/* [1] void*  */
+			BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),	/* [2] int    */
+			BTF_FUNC_PROTO_ENC(2, 1),			/* [3] int (*)(void*) */
+			BTF_FUNC_PROTO_ARG_ENC(8, 1),
+			BTF_FUNC_ENC(8, 3)			/* [4] FUNC 'foo' type_id=2   */
+		},
+		.strings = "\0int\0 0\0foo\0"
+	};
+	__u32 log_level = 1 | 2 | 4;
+	LIBBPF_OPTS(bpf_btf_load_opts, opts,
+		    .log_buf = log,
+		    .log_size = sizeof(log),
+		    .log_level = log_level,
+	);
+	struct bpf_insn insns[] = {
+		BPF_ALU64_IMM(BPF_MOV, BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	struct bpf_func_info funcs[] = {
+		{
+			.insn_off = 0,
+			.type_id = 4,
+		}
+	};
+	struct bpf_core_relo relos[] = {
+		{
+			.insn_off = 0,		/* patch first instruction (r0 = 0) */
+			.type_id = 100500,	/* !!! this type id does not exist */
+			.access_str_off = 6,	/* offset of "0" */
+			.kind = BPF_CORE_TYPE_ID_LOCAL,
+		}
+	};
+	union bpf_attr attr;
+	int saved_errno;
+	int prog_fd = -1;
+	int btf_fd = -1;
+
+	btf_fd = bpf_btf_load(&raw_btf, sizeof(raw_btf), &opts);
+	saved_errno = errno;
+	if (btf_fd < 0 || env.verbosity > VERBOSE_NORMAL) {
+		printf("-------- BTF load log start --------\n");
+		printf("%s", log);
+		printf("-------- BTF load log end ----------\n");
+	}
+	if (btf_fd < 0) {
+		PRINT_FAIL("bpf_btf_load() failed, errno=%d\n", saved_errno);
+		return;
+	}
+
+	log[0] = 0;
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_btf_fd = btf_fd;
+	attr.prog_type = BPF_TRACE_RAW_TP;
+	attr.license = (__u64)"GPL";
+	attr.insns = (__u64)&insns;
+	attr.insn_cnt = sizeof(insns) / sizeof(*insns);
+	attr.log_buf = (__u64)log;
+	attr.log_size = sizeof(log);
+	attr.log_level = log_level;
+	attr.func_info = (__u64)funcs;
+	attr.func_info_cnt = sizeof(funcs) / sizeof(*funcs);
+	attr.func_info_rec_size = sizeof(*funcs);
+	attr.core_relos = (__u64)relos;
+	attr.core_relo_cnt = sizeof(relos) / sizeof(*relos);
+	attr.core_relo_rec_size = sizeof(*relos);
+	prog_fd = sys_bpf_prog_load(&attr, sizeof(attr), 1);
+	saved_errno = errno;
+	if (prog_fd < 0 || env.verbosity > VERBOSE_NORMAL) {
+		printf("-------- program load log start --------\n");
+		printf("%s", log);
+		printf("-------- program load log end ----------\n");
+	}
+	if (prog_fd >= 0) {
+		PRINT_FAIL("sys_bpf_prog_load() expected to fail\n");
+		goto out;
+	}
+	ASSERT_HAS_SUBSTR(log, "relo #0: bad type id 100500", "program load log");
+
+out:
+	close(prog_fd);
+	close(btf_fd);
+}
+
+void test_core_reloc_raw(void)
+{
+	if (test__start_subtest("bad_local_id"))
+		test_bad_local_id();
+}