[PATCH bpf-next v2 10/11] selftests/bpf: Add negative test for greater-than-8-byte kfunc stack argument

Yonghong Song
2026-04-05T16:55:01Z

Add a test that the verifier rejects kfunc calls where a stack argument
exceeds 8 bytes (the register-sized slot limit).

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
.../selftests/bpf/prog_tests/stack_arg_fail.c | 24 ++++++++++++++
.../selftests/bpf/progs/stack_arg_fail.c | 32 +++++++++++++++++++
.../selftests/bpf/test_kmods/bpf_testmod.c | 7 ++++
.../bpf/test_kmods/bpf_testmod_kfunc.h | 8 +++++
4 files changed, 71 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/stack_arg_fail.c
create mode 100644 tools/testing/selftests/bpf/progs/stack_arg_fail.c

diff --git a/tools/testing/selftests/bpf/prog_tests/stack_arg_fail.c b/tools/testing/selftests/bpf/prog_tests/stack_arg_fail.c
new file mode 100644
index 000000000000..328a79edee45
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/stack_arg_fail.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include "stack_arg_fail.skel.h"
+
+void test_stack_arg_fail(void)
+{
+ struct stack_arg_fail *skel;
+
+ skel = stack_arg_fail__open();
+ if (!ASSERT_OK_PTR(skel, "open"))
+ return;
+
+ if (!skel->rodata->has_stack_arg) {
+ test__skip();
+ goto out;
+ }
+
+ ASSERT_ERR(stack_arg_fail__load(skel), "load_should_fail");
+
+out:
+ stack_arg_fail__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/stack_arg_fail.c b/tools/testing/selftests/bpf/progs/stack_arg_fail.c
new file mode 100644
index 000000000000..caa63b6f6a80
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/stack_arg_fail.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "../test_kmods/bpf_testmod_kfunc.h"
+
+#if defined(__BPF_FEATURE_STACK_ARGUMENT)
+
+const volatile bool has_stack_arg = true;
+
+SEC("tc")
+int test_stack_arg_big(struct __sk_buff *skb)
+{
+ struct prog_test_big_arg s = { .a = 1, .b = 2 };
+
+ return bpf_kfunc_call_stack_arg_big(1, 2, 3, 4, 5, s);
+}
+
+#else
+
+const volatile bool has_stack_arg = false;
+
+SEC("tc")
+int test_stack_arg_big(struct __sk_buff *skb)
+{
+ return 0;
+}
+
+#endif
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index 4fcdb13e4a9a..861c564cc330 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -881,6 +881,12 @@ __bpf_kfunc u64 bpf_kfunc_call_stack_arg_timer(u64 a, u64 b, u64 c, u64 d, u64 e
return a + b + c + d + e;
}

+__bpf_kfunc u64 bpf_kfunc_call_stack_arg_big(u64 a, u64 b, u64 c, u64 d, u64 e,
+ struct prog_test_big_arg s)
+{
+ return a + b + c + d + e + s.a + s.b;
+}
+
static struct prog_test_ref_kfunc prog_test_struct = {
.a = 42,
.b = 108,
@@ -1352,6 +1358,7 @@ BTF_ID_FLAGS(func, bpf_kfunc_call_stack_arg_mem)
BTF_ID_FLAGS(func, bpf_kfunc_call_stack_arg_iter)
BTF_ID_FLAGS(func, bpf_kfunc_call_stack_arg_const_str)
BTF_ID_FLAGS(func, bpf_kfunc_call_stack_arg_timer)
+BTF_ID_FLAGS(func, bpf_kfunc_call_stack_arg_big)
BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_pass1)
BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail1)
BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail2)
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
index 2c1cb118f886..2a40f80b074a 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
@@ -50,6 +50,11 @@ struct prog_test_pass2 {
} x;
};

+struct prog_test_big_arg {
+ long a;
+ long b;
+};
+
struct prog_test_fail1 {
void *p;
int x;
@@ -130,6 +135,9 @@ __u64 bpf_kfunc_call_stack_arg_const_str(__u64 a, __u64 b, __u64 c, __u64 d, __u
const char *str__str) __ksym;
__u64 bpf_kfunc_call_stack_arg_timer(__u64 a, __u64 b, __u64 c, __u64 d, __u64 e,
struct bpf_timer *timer) __ksym;
+__u64 bpf_kfunc_call_stack_arg_big(__u64 a, __u64 b, __u64 c, __u64 d, __u64 e,
+ struct prog_test_big_arg s) __ksym;
+
void bpf_kfunc_call_test_pass_ctx(struct __sk_buff *skb) __ksym;
void bpf_kfunc_call_test_pass1(struct prog_test_pass1 *p) __ksym;
void bpf_kfunc_call_test_pass2(struct prog_test_pass2 *p) __ksym;
--
2.52.0