selftests/bpf: Test case for lacking CFI stub functions.

Ensure struct_ops rejects the registration of struct_ops types without
proper CFI stub functions.

bpf_test_no_cfi.ko is a module that attempts to register a struct_ops type
called "bpf_test_no_cfi_ops" with cfi_stubs of NULL and non-NULL value.
The NULL one should fail, and the non-NULL one should succeed. The module
can only be loaded successfully if these registrations yield the expected
results.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Link: https://lore.kernel.org/r/20240222021105.1180475-3-thinker.li@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/Makefile

@@ -132,7 +132,7 @@ TEST_GEN_PROGS_EXTENDED = test_sock_addr test_skb_cgroup_id_user \
 	flow_dissector_load test_flow_dissector test_tcp_check_syncookie_user \
 	test_lirc_mode2_user xdping test_cpp runqslower bench bpf_testmod.ko \
 	xskxceiver xdp_redirect_multi xdp_synproxy veristat xdp_hw_metadata \
-	xdp_features
+	xdp_features bpf_test_no_cfi.ko
 
 TEST_GEN_FILES += liburandom_read.so urandom_read sign-file uprobe_multi
 
@@ -254,6 +254,12 @@ $(OUTPUT)/bpf_testmod.ko: $(VMLINUX_BTF) $(RESOLVE_BTFIDS) $(wildcard bpf_testmo
 	$(Q)$(MAKE) $(submake_extras) RESOLVE_BTFIDS=$(RESOLVE_BTFIDS) -C bpf_testmod
 	$(Q)cp bpf_testmod/bpf_testmod.ko $@
 
+$(OUTPUT)/bpf_test_no_cfi.ko: $(VMLINUX_BTF) $(RESOLVE_BTFIDS) $(wildcard bpf_test_no_cfi/Makefile bpf_test_no_cfi/*.[ch])
+	$(call msg,MOD,,$@)
+	$(Q)$(RM) bpf_test_no_cfi/bpf_test_no_cfi.ko # force re-compilation
+	$(Q)$(MAKE) $(submake_extras) RESOLVE_BTFIDS=$(RESOLVE_BTFIDS) -C bpf_test_no_cfi
+	$(Q)cp bpf_test_no_cfi/bpf_test_no_cfi.ko $@
+
 DEFAULT_BPFTOOL := $(HOST_SCRATCH_DIR)/sbin/bpftool
 ifneq ($(CROSS_COMPILE),)
 CROSS_BPFTOOL := $(SCRATCH_DIR)/sbin/bpftool
@@ -631,6 +637,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c		\
 			 flow_dissector_load.h	\
 			 ip_check_defrag_frags.h
 TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\
+		       $(OUTPUT)/bpf_test_no_cfi.ko			\
 		       $(OUTPUT)/liburandom_read.so			\
 		       $(OUTPUT)/xdp_synproxy				\
 		       $(OUTPUT)/sign-file				\
@@ -759,6 +766,7 @@ EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR)			\
 	feature bpftool							\
 	$(addprefix $(OUTPUT)/,*.o *.skel.h *.lskel.h *.subskel.h	\
 			       no_alu32 cpuv4 bpf_gcc bpf_testmod.ko	\
+			       bpf_test_no_cfi.ko			\
 			       liburandom_read.so)
 
 .PHONY: docs docs-clean

tools/testing/selftests/bpf/bpf_test_no_cfi/Makefile

@@ -0,0 +1,19 @@
+BPF_TEST_NO_CFI_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))
+KDIR ?= $(abspath $(BPF_TEST_NO_CFI_DIR)/../../../../..)
+
+ifeq ($(V),1)
+Q =
+else
+Q = @
+endif
+
+MODULES = bpf_test_no_cfi.ko
+
+obj-m += bpf_test_no_cfi.o
+
+all:
+	+$(Q)make -C $(KDIR) M=$(BPF_TEST_NO_CFI_DIR) modules
+
+clean:
+	+$(Q)make -C $(KDIR) M=$(BPF_TEST_NO_CFI_DIR) clean
+

tools/testing/selftests/bpf/bpf_test_no_cfi/bpf_test_no_cfi.c

@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/init.h>
+#include <linux/module.h>
+
+struct bpf_test_no_cfi_ops {
+	void (*fn_1)(void);
+	void (*fn_2)(void);
+};
+
+static int dummy_init(struct btf *btf)
+{
+	return 0;
+}
+
+static int dummy_init_member(const struct btf_type *t,
+			     const struct btf_member *member,
+			     void *kdata, const void *udata)
+{
+	return 0;
+}
+
+static int dummy_reg(void *kdata)
+{
+	return 0;
+}
+
+static void dummy_unreg(void *kdata)
+{
+}
+
+static const struct bpf_verifier_ops dummy_verifier_ops;
+
+static void bpf_test_no_cfi_ops__fn_1(void)
+{
+}
+
+static void bpf_test_no_cfi_ops__fn_2(void)
+{
+}
+
+static struct bpf_test_no_cfi_ops __test_no_cif_ops = {
+	.fn_1 = bpf_test_no_cfi_ops__fn_1,
+	.fn_2 = bpf_test_no_cfi_ops__fn_2,
+};
+
+static struct bpf_struct_ops test_no_cif_ops = {
+	.verifier_ops = &dummy_verifier_ops,
+	.init = dummy_init,
+	.init_member = dummy_init_member,
+	.reg = dummy_reg,
+	.unreg = dummy_unreg,
+	.name = "bpf_test_no_cfi_ops",
+	.owner = THIS_MODULE,
+};
+
+static int bpf_test_no_cfi_init(void)
+{
+	int ret;
+
+	ret = register_bpf_struct_ops(&test_no_cif_ops,
+				      bpf_test_no_cfi_ops);
+	if (!ret)
+		return -EINVAL;
+
+	test_no_cif_ops.cfi_stubs = &__test_no_cif_ops;
+	ret = register_bpf_struct_ops(&test_no_cif_ops,
+				      bpf_test_no_cfi_ops);
+	return ret;
+}
+
+static void bpf_test_no_cfi_exit(void)
+{
+}
+
+module_init(bpf_test_no_cfi_init);
+module_exit(bpf_test_no_cfi_exit);
+
+MODULE_AUTHOR("Kuifeng Lee");
+MODULE_DESCRIPTION("BPF no cfi_stubs test module");
+MODULE_LICENSE("Dual BSD/GPL");
+

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

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <testing_helpers.h>
+
+static void load_bpf_test_no_cfi(void)
+{
+	int fd;
+	int err;
+
+	fd = open("bpf_test_no_cfi.ko", O_RDONLY);
+	if (!ASSERT_GE(fd, 0, "open"))
+		return;
+
+	/* The module will try to register a struct_ops type without
+	 * cfi_stubs and with cfi_stubs.
+	 *
+	 * The one without cfi_stub should fail. The module will be loaded
+	 * successfully only if the result of the registration is as
+	 * expected, or it fails.
+	 */
+	err = finit_module(fd, "", 0);
+	close(fd);
+	if (!ASSERT_OK(err, "finit_module"))
+		return;
+
+	err = delete_module("bpf_test_no_cfi", 0);
+	ASSERT_OK(err, "delete_module");
+}
+
+void test_struct_ops_no_cfi(void)
+{
+	if (test__start_subtest("load_bpf_test_no_cfi"))
+		load_bpf_test_no_cfi();
+}

tools/testing/selftests/bpf/testing_helpers.c

@@ -356,12 +356,12 @@ __u64 read_perf_max_sample_freq(void)
 	return sample_freq;
 }
 
-static int finit_module(int fd, const char *param_values, int flags)
+int finit_module(int fd, const char *param_values, int flags)
 {
 	return syscall(__NR_finit_module, fd, param_values, flags);
 }
 
-static int delete_module(const char *name, int flags)
+int delete_module(const char *name, int flags)
 {
 	return syscall(__NR_delete_module, name, flags);
 }

tools/testing/selftests/bpf/testing_helpers.h

@@ -36,6 +36,8 @@ __u64 read_perf_max_sample_freq(void);
 int load_bpf_testmod(bool verbose);
 int unload_bpf_testmod(bool verbose);
 int kern_sync_rcu(void);
+int finit_module(int fd, const char *param_values, int flags);
+int delete_module(const char *name, int flags);
 
 static inline __u64 get_time_ns(void)
 {