bpf/selftests: coverage for bpf_map_ops errors

These tests expose the issue of being unable to properly check for errors
returned from inlined bpf map helpers that make calls to the bpf_map_ops
functions. At best, a check for zero or non-zero can be done but these
tests show it is not possible to check for a negative value or for a
specific error value.

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230322194754.185781-2-inwardvessel@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 138 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_map_ops.c b/tools/testing/selftests/bpf/progs/test_map_ops.c
new file mode 100644
index 000000000000..b53b46a090c8
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_map_ops.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} hash_map SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_STACK);
+	__uint(max_entries, 1);
+	__type(value, int);
+} stack_map SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} array_map SEC(".maps");
+
+const volatile pid_t pid;
+long err = 0;
+
+static u64 callback(u64 map, u64 key, u64 val, u64 ctx, u64 flags)
+{
+	return 0;
+}
+
+SEC("tp/syscalls/sys_enter_getpid")
+int map_update(void *ctx)
+{
+	const int key = 0;
+	const int val = 1;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	err = bpf_map_update_elem(&hash_map, &key, &val, BPF_NOEXIST);
+
+	return 0;
+}
+
+SEC("tp/syscalls/sys_enter_getppid")
+int map_delete(void *ctx)
+{
+	const int key = 0;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	err = bpf_map_delete_elem(&hash_map, &key);
+
+	return 0;
+}
+
+SEC("tp/syscalls/sys_enter_getuid")
+int map_push(void *ctx)
+{
+	const int val = 1;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	err = bpf_map_push_elem(&stack_map, &val, 0);
+
+	return 0;
+}
+
+SEC("tp/syscalls/sys_enter_geteuid")
+int map_pop(void *ctx)
+{
+	int val;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	err = bpf_map_pop_elem(&stack_map, &val);
+
+	return 0;
+}
+
+SEC("tp/syscalls/sys_enter_getgid")
+int map_peek(void *ctx)
+{
+	int val;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	err = bpf_map_peek_elem(&stack_map, &val);
+
+	return 0;
+}
+
+SEC("tp/syscalls/sys_enter_gettid")
+int map_for_each_pass(void *ctx)
+{
+	const int key = 0;
+	const int val = 1;
+	const u64 flags = 0;
+	int callback_ctx;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	bpf_map_update_elem(&array_map, &key, &val, flags);
+
+	err = bpf_for_each_map_elem(&array_map, callback, &callback_ctx, flags);
+
+	return 0;
+}
+
+SEC("tp/syscalls/sys_enter_getpgid")
+int map_for_each_fail(void *ctx)
+{
+	const int key = 0;
+	const int val = 1;
+	const u64 flags = BPF_NOEXIST;
+	int callback_ctx;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	bpf_map_update_elem(&array_map, &key, &val, flags);
+
+	/* calling for_each with non-zero flags will return error */
+	err = bpf_for_each_map_elem(&array_map, callback, &callback_ctx, flags);
+
+	return 0;
+}