selftests/bpf: Add bpf_testmod kernel module for testing

Add bpf_testmod module, which is conceptually out-of-tree module and provides
ways for selftests/bpf to test various kernel module-related functionality:
raw tracepoint, fentry/fexit/fmod_ret, etc. This module will be auto-loaded by
test_progs test runner and expected by some of selftests to be present and
loaded.

Pahole currently isn't able to generate BTF for static functions in kernel
modules, so make sure traced function is global.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201203204634.1325171-7-andrii@kernel.org

tools/testing/selftests/bpf/.gitignore

@@ -35,3 +35,4 @@ test_cpp
 /tools
 /runqslower
 /bench
+*.ko

tools/testing/selftests/bpf/Makefile

@@ -80,7 +80,7 @@ TEST_PROGS_EXTENDED := with_addr.sh \
 # Compile but not part of 'make run_tests'
 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
+	test_lirc_mode2_user xdping test_cpp runqslower bench bpf_testmod.ko
 
 TEST_CUSTOM_PROGS = urandom_read
 
@@ -104,6 +104,7 @@ OVERRIDE_TARGETS := 1
 override define CLEAN
 	$(call msg,CLEAN)
 	$(Q)$(RM) -r $(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED) $(TEST_GEN_FILES) $(EXTRA_CLEAN)
+	$(Q)$(MAKE) -C bpf_testmod clean
 endef
 
 include ../lib.mk
@@ -136,6 +137,11 @@ $(OUTPUT)/urandom_read: urandom_read.c
 	$(call msg,BINARY,,$@)
 	$(Q)$(CC) $(LDFLAGS) -o $@ $< $(LDLIBS) -Wl,--build-id=sha1
 
+$(OUTPUT)/bpf_testmod.ko: $(VMLINUX_BTF) $(wildcard bpf_testmod/Makefile bpf_testmod/*.[ch])
+	$(call msg,MOD,,$@)
+	$(Q)$(MAKE) $(submake_extras) -C bpf_testmod
+	$(Q)cp bpf_testmod/bpf_testmod.ko $@
+
 $(OUTPUT)/test_stub.o: test_stub.c $(BPFOBJ)
 	$(call msg,CC,,$@)
 	$(Q)$(CC) -c $(CFLAGS) -o $@ $<
@@ -388,7 +394,7 @@ TRUNNER_BPF_PROGS_DIR := progs
 TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
 			 network_helpers.c testing_helpers.c		\
 			 btf_helpers.c	flow_dissector_load.h
-TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read				\
+TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\
 		       ima_setup.sh					\
 		       $(wildcard progs/btf_dump_test_case_*.c)
 TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
@@ -460,4 +466,4 @@ $(OUTPUT)/bench: $(OUTPUT)/bench.o $(OUTPUT)/testing_helpers.o \
 EXTRA_CLEAN := $(TEST_CUSTOM_PROGS) $(SCRATCH_DIR)			\
 	prog_tests/tests.h map_tests/tests.h verifier/tests.h		\
 	feature								\
-	$(addprefix $(OUTPUT)/,*.o *.skel.h no_alu32 bpf_gcc)
+	$(addprefix $(OUTPUT)/,*.o *.skel.h no_alu32 bpf_gcc bpf_testmod.ko)

tools/testing/selftests/bpf/bpf_testmod/.gitignore

@@ -0,0 +1,6 @@
+*.mod
+*.mod.c
+*.o
+.ko
+/Module.symvers
+/modules.order

tools/testing/selftests/bpf/bpf_testmod/Makefile

@@ -0,0 +1,20 @@
+BPF_TESTMOD_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))
+KDIR ?= $(abspath $(BPF_TESTMOD_DIR)/../../../../..)
+
+ifeq ($(V),1)
+Q =
+else
+Q = @
+endif
+
+MODULES = bpf_testmod.ko
+
+obj-m += bpf_testmod.o
+CFLAGS_bpf_testmod.o = -I$(src)
+
+all:
+	+$(Q)make -C $(KDIR) M=$(BPF_TESTMOD_DIR) modules
+
+clean:
+	+$(Q)make -C $(KDIR) M=$(BPF_TESTMOD_DIR) clean
+

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h

@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2020 Facebook */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM bpf_testmod
+
+#if !defined(_BPF_TESTMOD_EVENTS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _BPF_TESTMOD_EVENTS_H
+
+#include <linux/tracepoint.h>
+#include "bpf_testmod.h"
+
+TRACE_EVENT(bpf_testmod_test_read,
+	TP_PROTO(struct task_struct *task, struct bpf_testmod_test_read_ctx *ctx),
+	TP_ARGS(task, ctx),
+	TP_STRUCT__entry(
+		__field(pid_t, pid)
+		__array(char, comm, TASK_COMM_LEN)
+		__field(loff_t, off)
+		__field(size_t, len)
+	),
+	TP_fast_assign(
+		__entry->pid = task->pid;
+		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+		__entry->off = ctx->off;
+		__entry->len = ctx->len;
+	),
+	TP_printk("pid=%d comm=%s off=%llu len=%zu",
+		  __entry->pid, __entry->comm, __entry->off, __entry->len)
+);
+
+#endif /* _BPF_TESTMOD_EVENTS_H */
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE bpf_testmod-events
+#include <trace/define_trace.h>

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <linux/error-injection.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/sysfs.h>
+#include <linux/tracepoint.h>
+#include "bpf_testmod.h"
+
+#define CREATE_TRACE_POINTS
+#include "bpf_testmod-events.h"
+
+noinline ssize_t
+bpf_testmod_test_read(struct file *file, struct kobject *kobj,
+		      struct bin_attribute *bin_attr,
+		      char *buf, loff_t off, size_t len)
+{
+	struct bpf_testmod_test_read_ctx ctx = {
+		.buf = buf,
+		.off = off,
+		.len = len,
+	};
+
+	trace_bpf_testmod_test_read(current, &ctx);
+
+	return -EIO; /* always fail */
+}
+EXPORT_SYMBOL(bpf_testmod_test_read);
+ALLOW_ERROR_INJECTION(bpf_testmod_test_read, ERRNO);
+
+static struct bin_attribute bin_attr_bpf_testmod_file __ro_after_init = {
+	.attr = { .name = "bpf_testmod", .mode = 0444, },
+	.read = bpf_testmod_test_read,
+};
+
+static int bpf_testmod_init(void)
+{
+	return sysfs_create_bin_file(kernel_kobj, &bin_attr_bpf_testmod_file);
+}
+
+static void bpf_testmod_exit(void)
+{
+	return sysfs_remove_bin_file(kernel_kobj, &bin_attr_bpf_testmod_file);
+}
+
+module_init(bpf_testmod_init);
+module_exit(bpf_testmod_exit);
+
+MODULE_AUTHOR("Andrii Nakryiko");
+MODULE_DESCRIPTION("BPF selftests module");
+MODULE_LICENSE("Dual BSD/GPL");
+

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2020 Facebook */
+#ifndef _BPF_TESTMOD_H
+#define _BPF_TESTMOD_H
+
+#include <linux/types.h>
+
+struct bpf_testmod_test_read_ctx {
+	char *buf;
+	loff_t off;
+	size_t len;
+};
+
+#endif /* _BPF_TESTMOD_H */

tools/testing/selftests/bpf/test_progs.c

@@ -360,6 +360,58 @@ int extract_build_id(char *build_id, size_t size)
 	return -1;
 }
 
+static 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)
+{
+	return syscall(__NR_delete_module, name, flags);
+}
+
+static void unload_bpf_testmod(void)
+{
+	if (delete_module("bpf_testmod", 0)) {
+		if (errno == ENOENT) {
+			if (env.verbosity > VERBOSE_NONE)
+				fprintf(stdout, "bpf_testmod.ko is already unloaded.\n");
+			return;
+		}
+		fprintf(env.stderr, "Failed to unload bpf_testmod.ko from kernel: %d\n", -errno);
+		exit(1);
+	}
+	if (env.verbosity > VERBOSE_NONE)
+		fprintf(stdout, "Successfully unloaded bpf_testmod.ko.\n");
+}
+
+static int load_bpf_testmod(void)
+{
+	int fd;
+
+	/* ensure previous instance of the module is unloaded */
+	unload_bpf_testmod();
+
+	if (env.verbosity > VERBOSE_NONE)
+		fprintf(stdout, "Loading bpf_testmod.ko...\n");
+
+	fd = open("bpf_testmod.ko", O_RDONLY);
+	if (fd < 0) {
+		fprintf(env.stderr, "Can't find bpf_testmod.ko kernel module: %d\n", -errno);
+		return -ENOENT;
+	}
+	if (finit_module(fd, "", 0)) {
+		fprintf(env.stderr, "Failed to load bpf_testmod.ko into the kernel: %d\n", -errno);
+		close(fd);
+		return -EINVAL;
+	}
+	close(fd);
+
+	if (env.verbosity > VERBOSE_NONE)
+		fprintf(stdout, "Successfully loaded bpf_testmod.ko.\n");
+	return 0;
+}
+
 /* extern declarations for test funcs */
 #define DEFINE_TEST(name) extern void test_##name(void);
 #include <prog_tests/tests.h>
@@ -678,6 +730,11 @@ int main(int argc, char **argv)
 
 	save_netns();
 	stdio_hijack();
+	env.has_testmod = true;
+	if (load_bpf_testmod()) {
+		fprintf(env.stderr, "WARNING! Selftests relying on bpf_testmod.ko will be skipped.\n");
+		env.has_testmod = false;
+	}
 	for (i = 0; i < prog_test_cnt; i++) {
 		struct prog_test_def *test = &prog_test_defs[i];
 
@@ -722,6 +779,8 @@ int main(int argc, char **argv)
 		if (test->need_cgroup_cleanup)
 			cleanup_cgroup_environment();
 	}
+	if (env.has_testmod)
+		unload_bpf_testmod();
 	stdio_restore();
 
 	if (env.get_test_cnt) {

tools/testing/selftests/bpf/test_progs.h

@@ -66,6 +66,7 @@ struct test_env {
 	enum verbosity verbosity;
 
 	bool jit_enabled;
+	bool has_testmod;
 	bool get_test_cnt;
 	bool list_test_names;