selftests/bpf: Add unit tests for pointers in global functions

test_global_func9 - check valid pointer's scenarios
test_global_func10 - check that a smaller type cannot be passed as a
larger one
test_global_func11 - check that CTX pointer cannot be passed
test_global_func12 - check access to a null pointer
test_global_func13 - check access to an arbitrary pointer value
test_global_func14 - check that an opaque pointer cannot be passed
test_global_func15 - check that a variable has an unknown value after
it was passed to a global function by pointer
test_global_func16 - check access to uninitialized stack memory

test_global_func_args - check read and write operations through a pointer

Signed-off-by: Dmitrii Banshchikov <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
+// SPDX-License-Identifier: GPL-2.0
+#include "test_progs.h"
+#include "network_helpers.h"
+
+static __u32 duration;
+
+static void test_global_func_args0(struct bpf_object *obj)
+{
+	int err, i, map_fd, actual_value;
+	const char *map_name = "values";
+
+	map_fd = bpf_find_map(__func__, obj, map_name);
+	if (CHECK(map_fd < 0, "bpf_find_map", "cannot find BPF map %s: %s\n",
+		map_name, strerror(errno)))
+		return;
+
+	struct {
+		const char *descr;
+		int expected_value;
+	} tests[] = {
+		{"passing NULL pointer", 0},
+		{"returning value", 1},
+		{"reading local variable", 100 },
+		{"writing local variable", 101 },
+		{"reading global variable", 42 },
+		{"writing global variable", 43 },
+		{"writing to pointer-to-pointer", 1 },
+	};
+
+	for (i = 0; i < ARRAY_SIZE(tests); ++i) {
+		const int expected_value = tests[i].expected_value;
+
+		err = bpf_map_lookup_elem(map_fd, &i, &actual_value);
+
+		CHECK(err || actual_value != expected_value, tests[i].descr,
+			 "err %d result %d expected %d\n", err, actual_value, expected_value);
+	}
+}
+
+void test_global_func_args(void)
+{
+	const char *file = "./test_global_func_args.o";
+	__u32 retval;
+	struct bpf_object *obj;
+	int err, prog_fd;
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_CGROUP_SKB, &obj, &prog_fd);
+	if (CHECK(err, "load program", "error %d loading %s\n", err, file))
+		return;
+
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, &retval, &duration);
+	CHECK(err || retval, "pass global func args run",
+	      "err %d errno %d retval %d duration %d\n",
+	      err, errno, retval, duration);
+
+	test_global_func_args0(obj);
+
+	bpf_object__close(obj);
+}

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

···
 		{ "test_global_func6.o" , "modified ctx ptr R2" },
 		{ "test_global_func7.o" , "foo() doesn't return scalar" },
 		{ "test_global_func8.o" },
+		{ "test_global_func9.o" },
+		{ "test_global_func10.o", "invalid indirect read from stack" },
+		{ "test_global_func11.o", "Caller passes invalid args into func#1" },
+		{ "test_global_func12.o", "invalid mem access 'mem_or_null'" },
+		{ "test_global_func13.o", "Caller passes invalid args into func#1" },
+		{ "test_global_func14.o", "reference type('FWD S') size cannot be determined" },
+		{ "test_global_func15.o", "At program exit the register R0 has value" },
+		{ "test_global_func16.o", "invalid indirect read from stack" },
 	};
 	libbpf_print_fn_t old_print_fn = NULL;
 	int err, i, duration = 0;

tools/testing/selftests/bpf/progs/test_global_func10.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct Small {
+	int x;
+};
+
+struct Big {
+	int x;
+	int y;
+};
+
+__noinline int foo(const struct Big *big)
+{
+	if (big == 0)
+		return 0;
+
+	return bpf_get_prandom_u32() < big->y;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	const struct Small small = {.x = skb->len };
+
+	return foo((struct Big *)&small) ? 1 : 0;
+}

tools/testing/selftests/bpf/progs/test_global_func11.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct S {
+	int x;
+};
+
+__noinline int foo(const struct S *s)
+{
+	return s ? bpf_get_prandom_u32() < s->x : 0;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	return foo(skb);
+}

tools/testing/selftests/bpf/progs/test_global_func12.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct S {
+	int x;
+};
+
+__noinline int foo(const struct S *s)
+{
+	return bpf_get_prandom_u32() < s->x;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	const struct S s = {.x = skb->len };
+
+	return foo(&s);
+}

tools/testing/selftests/bpf/progs/test_global_func13.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct S {
+	int x;
+};
+
+__noinline int foo(const struct S *s)
+{
+	if (s)
+		return bpf_get_prandom_u32() < s->x;
+
+	return 0;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	const struct S *s = (const struct S *)(0xbedabeda);
+
+	return foo(s);
+}

tools/testing/selftests/bpf/progs/test_global_func14.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct S;
+
+__noinline int foo(const struct S *s)
+{
+	if (s)
+		return bpf_get_prandom_u32() < *(const int *) s;
+
+	return 0;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+
+	return foo(NULL);
+}

tools/testing/selftests/bpf/progs/test_global_func15.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+__noinline int foo(unsigned int *v)
+{
+	if (v)
+		*v = bpf_get_prandom_u32();
+
+	return 0;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	unsigned int v = 1;
+
+	foo(&v);
+
+	return v;
+}

tools/testing/selftests/bpf/progs/test_global_func16.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+__noinline int foo(int (*arr)[10])
+{
+	if (arr)
+		return (*arr)[9];
+
+	return 0;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	int array[10];
+
+	const int rv = foo(&array);
+
+	return rv ? 1 : 0;
+}

tools/testing/selftests/bpf/progs/test_global_func9.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct S {
+	int x;
+};
+
+struct C {
+	int x;
+	int y;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, struct S);
+} map SEC(".maps");
+
+enum E {
+	E_ITEM
+};
+
+static int global_data_x = 100;
+static int volatile global_data_y = 500;
+
+__noinline int foo(const struct S *s)
+{
+	if (s)
+		return bpf_get_prandom_u32() < s->x;
+
+	return 0;
+}
+
+__noinline int bar(int *x)
+{
+	if (x)
+		*x &= bpf_get_prandom_u32();
+
+	return 0;
+}
+__noinline int baz(volatile int *x)
+{
+	if (x)
+		*x &= bpf_get_prandom_u32();
+
+	return 0;
+}
+
+__noinline int qux(enum E *e)
+{
+	if (e)
+		return *e;
+
+	return 0;
+}
+
+__noinline int quux(int (*arr)[10])
+{
+	if (arr)
+		return (*arr)[9];
+
+	return 0;
+}
+
+__noinline int quuz(int **p)
+{
+	if (p)
+		*p = NULL;
+
+	return 0;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	int result = 0;
+
+	{
+		const struct S s = {.x = skb->len };
+
+		result |= foo(&s);
+	}
+
+	{
+		const __u32 key = 1;
+		const struct S *s = bpf_map_lookup_elem(&map, &key);
+
+		result |= foo(s);
+	}
+
+	{
+		const struct C c = {.x = skb->len, .y = skb->family };
+
+		result |= foo((const struct S *)&c);
+	}
+
+	{
+		result |= foo(NULL);
+	}
+
+	{
+		bar(&result);
+		bar(&global_data_x);
+	}
+
+	{
+		result |= baz(&global_data_y);
+	}
+
+	{
+		enum E e = E_ITEM;
+
+		result |= qux(&e);
+	}
+
+	{
+		int array[10] = {0};
+
+		result |= quux(&array);
+	}
+
+	{
+		int *p;
+
+		result |= quuz(&p);
+	}
+
+	return result ? 1 : 0;
+}

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

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+
+#include <bpf/bpf_helpers.h>
+
+struct S {
+	int v;
+};
+
+static volatile struct S global_variable;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 7);
+	__type(key, __u32);
+	__type(value, int);
+} values SEC(".maps");
+
+static void save_value(__u32 index, int value)
+{
+	bpf_map_update_elem(&values, &index, &value, 0);
+}
+
+__noinline int foo(__u32 index, struct S *s)
+{
+	if (s) {
+		save_value(index, s->v);
+		return ++s->v;
+	}
+
+	save_value(index, 0);
+
+	return 1;
+}
+
+__noinline int bar(__u32 index, volatile struct S *s)
+{
+	if (s) {
+		save_value(index, s->v);
+		return ++s->v;
+	}
+
+	save_value(index, 0);
+
+	return 1;
+}
+
+__noinline int baz(struct S **s)
+{
+	if (s)
+		*s = 0;
+
+	return 0;
+}
+
+SEC("cgroup_skb/ingress")
+int test_cls(struct __sk_buff *skb)
+{
+	__u32 index = 0;
+
+	{
+		const int v = foo(index++, 0);
+
+		save_value(index++, v);
+	}
+
+	{
+		struct S s = { .v = 100 };
+
+		foo(index++, &s);
+		save_value(index++, s.v);
+	}
+
+	{
+		global_variable.v = 42;
+		bar(index++, &global_variable);
+		save_value(index++, global_variable.v);
+	}
+
+	{
+		struct S v, *p = &v;
+
+		baz(&p);
+		save_value(index++, !p);
+	}
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";