selftests/bpf: Add test for zero offset or non-zero offset pointers as KF_ACQUIRE kfuncs argument

This patch adds test cases for zero offset (implicit cast) or non-zero
offset pointer as KF_ACQUIRE kfuncs argument. Currently KF_ACQUIRE
kfuncs should support passing in pointers like &sk->sk_write_queue
(non-zero offset) or &sk->__sk_common (zero offset) and not be rejected
by the verifier.

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

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

···
 {
 }
 
+__bpf_kfunc struct sk_buff *bpf_kfunc_nested_acquire_nonzero_offset_test(struct sk_buff_head *ptr)
+{
+	return NULL;
+}
+
+__bpf_kfunc struct sk_buff *bpf_kfunc_nested_acquire_zero_offset_test(struct sock_common *ptr)
+{
+	return NULL;
+}
+
+__bpf_kfunc void bpf_kfunc_nested_release_test(struct sk_buff *ptr)
+{
+}
+
 __bpf_kfunc struct bpf_testmod_ctx *
 bpf_testmod_ctx_create(int *err)
 {
···
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_value)
 BTF_ID_FLAGS(func, bpf_kfunc_common_test)
 BTF_ID_FLAGS(func, bpf_kfunc_dynptr_test)
+BTF_ID_FLAGS(func, bpf_kfunc_nested_acquire_nonzero_offset_test, KF_ACQUIRE)
+BTF_ID_FLAGS(func, bpf_kfunc_nested_acquire_zero_offset_test, KF_ACQUIRE)
+BTF_ID_FLAGS(func, bpf_kfunc_nested_release_test, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_testmod_ctx_create, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_testmod_ctx_release, KF_RELEASE)
 BTF_KFUNCS_END(bpf_testmod_common_kfunc_ids)

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

···
 struct bpf_testmod_ctx *bpf_testmod_ctx_create(int *err) __ksym;
 void bpf_testmod_ctx_release(struct bpf_testmod_ctx *ctx) __ksym;
 
+struct sk_buff *bpf_kfunc_nested_acquire_nonzero_offset_test(struct sk_buff_head *ptr) __ksym;
+struct sk_buff *bpf_kfunc_nested_acquire_zero_offset_test(struct sock_common *ptr) __ksym;
+void bpf_kfunc_nested_release_test(struct sk_buff *ptr) __ksym;
+
 #endif /* _BPF_TESTMOD_KFUNC_H */

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

···
 #include <test_progs.h>
 #include "nested_trust_failure.skel.h"
 #include "nested_trust_success.skel.h"
+#include "nested_acquire.skel.h"
 
 void test_nested_trust(void)
 {
 	RUN_TESTS(nested_trust_success);
 	RUN_TESTS(nested_trust_failure);
+
+	if (env.has_testmod)
+		RUN_TESTS(nested_acquire);
 }

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

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "../bpf_testmod/bpf_testmod_kfunc.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("tp_btf/tcp_probe")
+__success
+int BPF_PROG(test_nested_acquire_nonzero, struct sock *sk, struct sk_buff *skb)
+{
+	struct sk_buff *ptr;
+
+	ptr = bpf_kfunc_nested_acquire_nonzero_offset_test(&sk->sk_write_queue);
+
+	bpf_kfunc_nested_release_test(ptr);
+	return 0;
+}
+
+SEC("tp_btf/tcp_probe")
+__success
+int BPF_PROG(test_nested_acquire_zero, struct sock *sk, struct sk_buff *skb)
+{
+	struct sk_buff *ptr;
+
+	ptr = bpf_kfunc_nested_acquire_zero_offset_test(&sk->__sk_common);
+
+	bpf_kfunc_nested_release_test(ptr);
+	return 0;
+}