selftests/bpf: Test module kfunc calls under spin lock

The verifier uses kfunc registration flags to decide whether a kfunc may
be called while a BPF program holds a bpf_spin_lock.

Mark bpf_testmod_test_mod_kfunc() as KF_SPINLOCK_SAFE and verify that it
can be called while holding a bpf_spin_lock. Also attempt to call the
unmarked bpf_kfunc_trigger_ctx_check() under the lock and verify that the
program is rejected.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Acked-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/bpf/20260805153340.34776-4-kaitao.cheng@linux.dev
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

4 files changed, 27 insertions, 1 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
index 7af5560f2a08..2b39cc1b09f9 100644
--- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
+++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
@@ -71,8 +71,10 @@ static struct kfunc_test_params kfunc_tests[] = {
 	TC_FAIL(kfunc_call_test_get_mem_fail_not_const, 0, "is not a const"),
 	TC_FAIL(kfunc_call_test_mem_acquire_fail, 0, "acquire kernel function does not return PTR_TO_BTF_ID"),
 	TC_FAIL(kfunc_call_test_pointer_arg_type_mismatch, 0, "R1 expected pointer to ctx, but got scalar"),
+	TC_FAIL(kfunc_call_test_spin_lock_unsafe, 0, "function calls are not allowed while holding a lock"),
 
 	/* success cases */
+	TC_TEST(kfunc_call_test_spin_lock_safe, 0),
 	TC_TEST(kfunc_call_test1, 12),
 	TC_TEST(kfunc_call_test2, 3),
 	TC_TEST(kfunc_call_test4, -1234),
diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_fail.c b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
index 64b6a0b0ab1c..7e93f7fb1329 100644
--- a/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
+++ b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
@@ -4,6 +4,18 @@
 #include <bpf/bpf_helpers.h>
 #include "../test_kmods/bpf_testmod_kfunc.h"
 
+static struct bpf_spin_lock kfunc_call_lock SEC(".data.A");
+
+SEC("?tc")
+int kfunc_call_test_spin_lock_unsafe(struct __sk_buff *skb)
+{
+	bpf_spin_lock(&kfunc_call_lock);
+	bpf_kfunc_trigger_ctx_check();
+	bpf_spin_unlock(&kfunc_call_lock);
+
+	return 0;
+}
+
 struct syscall_test_args {
 	__u8 data[16];
 	size_t size;
diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_test.c b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
index 5edc51564f71..8e6560c31e78 100644
--- a/tools/testing/selftests/bpf/progs/kfunc_call_test.c
+++ b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
@@ -5,6 +5,18 @@
 #include "bpf_misc.h"
 #include "../test_kmods/bpf_testmod_kfunc.h"
 
+static struct bpf_spin_lock kfunc_call_lock SEC(".data.A");
+
+SEC("tc")
+int kfunc_call_test_spin_lock_safe(struct __sk_buff *skb)
+{
+	bpf_spin_lock(&kfunc_call_lock);
+	bpf_testmod_test_mod_kfunc(42);
+	bpf_spin_unlock(&kfunc_call_lock);
+
+	return 0;
+}
+
 SEC("tc")
 int kfunc_call_test5(struct __sk_buff *skb)
 {
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index eb0f9b5e18d8..0585794606ed 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -1384,7 +1384,7 @@ __bpf_kfunc void bpf_kfunc_trigger_ctx_check(void)
 }
 
 BTF_KFUNCS_START(bpf_testmod_check_kfunc_ids)
-BTF_ID_FLAGS(func, bpf_testmod_test_mod_kfunc)
+BTF_ID_FLAGS(func, bpf_testmod_test_mod_kfunc, KF_SPINLOCK_SAFE)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test1)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test2)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test3)