[PATCHv2 bpf-next 4/8] selftests/bpf: Test const kfunc memory arguments

[Jiri Olsa <jolsa@kernel.org>]

Verify that const kfunc arguments accept read-only global data,
writable stack data, and const scalar structs. Check that read-only
data is rejected when passed to a writable memory argument.

Assisted-by: Codex:GPT-6
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 .../testing/selftests/bpf/prog_tests/kfunc_call.c  |  2 ++
 .../testing/selftests/bpf/progs/kfunc_call_fail.c  | 10 ++++++++++
 .../testing/selftests/bpf/progs/kfunc_call_test.c  | 14 ++++++++++++++
 .../testing/selftests/bpf/test_kmods/bpf_testmod.c | 10 ++++++++++
 .../selftests/bpf/test_kmods/bpf_testmod_kfunc.h   |  2 ++
 5 files changed, 38 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
index 0063e60d6f2f..f2152591982b 100644
--- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
+++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
@@ -63,6 +63,7 @@ static struct kfunc_test_params kfunc_tests[] = {
 	 */
 	SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_fail, -EINVAL, "processed 4 insns"),
 	SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_null_fail, -EINVAL, "processed 4 insns"),
+	TC_FAIL(kfunc_call_test_mem_len_fail_readonly, 0, "write into map forbidden"),
 	TC_FAIL(kfunc_call_test_get_mem_fail_rdonly, 0, "R0 cannot write into rdonly_mem"),
 	TC_FAIL(kfunc_call_test_get_mem_fail_use_after_free, 0, "invalid mem access 'scalar'"),
 	TC_FAIL(kfunc_call_test_get_mem_fail_oob, 0, "min value is outside of the allowed memory range"),
@@ -82,6 +83,7 @@ static struct kfunc_test_params kfunc_tests[] = {
 	TC_TEST(kfunc_call_test5_asm, 0),
 	TC_TEST(kfunc_call_test_ref_btf_id, 0),
 	TC_TEST(kfunc_call_test_get_mem, 42),
+	TC_TEST(kfunc_call_test_const_mem, 0),
 	SYSCALL_TEST(kfunc_syscall_test, 0),
 	SYSCALL_NULL_CTX_TEST(kfunc_syscall_test_null, 0),
 	TC_TEST(kfunc_call_test_static_unused_arg, 0),
diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_fail.c b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
index 7e93f7fb1329..bef956d3f89e 100644
--- a/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
+++ b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
@@ -4,6 +4,8 @@
 #include <bpf/bpf_helpers.h>
 #include "../test_kmods/bpf_testmod_kfunc.h"
 
+static const char kfunc_mem_rodata[] = "read-only data";
+
 static struct bpf_spin_lock kfunc_call_lock SEC(".data.A");
 
 SEC("?tc")
@@ -47,6 +49,14 @@ int kfunc_syscall_test_null_fail(struct syscall_test_args *args)
 	return 0;
 }
 
+SEC("?tc")
+int kfunc_call_test_mem_len_fail_readonly(struct __sk_buff *skb)
+{
+	bpf_kfunc_call_test_mem_len_pass1((void *)kfunc_mem_rodata,
+					  sizeof(kfunc_mem_rodata));
+	return 0;
+}
+
 SEC("?tc")
 int kfunc_call_test_get_mem_fail_rdonly(struct __sk_buff *skb)
 {
diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_test.c b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
index 8e6560c31e78..4f4a6713aa6e 100644
--- a/tools/testing/selftests/bpf/progs/kfunc_call_test.c
+++ b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
@@ -5,6 +5,9 @@
 #include "bpf_misc.h"
 #include "../test_kmods/bpf_testmod_kfunc.h"
 
+static const char kfunc_const_data[] = "read-only source";
+static const struct prog_test_pass1 kfunc_const_struct = { .x0 = 1 };
+
 static struct bpf_spin_lock kfunc_call_lock SEC(".data.A");
 
 SEC("tc")
@@ -208,6 +211,17 @@ int kfunc_call_test_pass(struct __sk_buff *skb)
 	return 0;
 }
 
+SEC("tc")
+int kfunc_call_test_const_mem(struct __sk_buff *skb)
+{
+	char stack_data[] = "read-write";
+
+	bpf_kfunc_call_test_const_mem(kfunc_const_data, sizeof(kfunc_const_data));
+	bpf_kfunc_call_test_const_mem(stack_data, sizeof(stack_data));
+	bpf_kfunc_call_test_const_struct(&kfunc_const_struct);
+	return 0;
+}
+
 struct syscall_test_args {
 	__u8 data[16];
 	size_t size;
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index 76fbe64755ef..41ff36f0ca77 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -1049,6 +1049,8 @@ BTF_ID_FLAGS(func, bpf_kfunc_arena_args5_test)
 BTF_ID_FLAGS(func, bpf_kfunc_arena_stack_arg_test)
 BTF_ID_FLAGS(func, bpf_kfunc_arena_mixed_test)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_pass1)
+BTF_ID_FLAGS(func, bpf_kfunc_call_test_const_mem)
+BTF_ID_FLAGS(func, bpf_kfunc_call_test_const_struct)
 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)
@@ -1552,6 +1554,14 @@ __bpf_kfunc void bpf_kfunc_call_test_mem_len_pass1(void *mem, int mem__sz)
 {
 }
 
+__bpf_kfunc void bpf_kfunc_call_test_const_mem(const void *mem, int mem__sz)
+{
+}
+
+__bpf_kfunc void bpf_kfunc_call_test_const_struct(const struct prog_test_pass1 *p)
+{
+}
+
 __bpf_kfunc void bpf_kfunc_call_test_mem_len_fail1(void *mem, int len)
 {
 }
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 e9902e651d72..0a7df1798603 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
@@ -203,6 +203,8 @@ void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p) __ksym;
 void bpf_kfunc_call_test_ref(struct prog_test_ref_kfunc *p) __ksym;
 
 void bpf_kfunc_call_test_mem_len_pass1(void *mem, int len) __ksym;
+void bpf_kfunc_call_test_const_mem(const void *mem, int mem__sz) __ksym;
+void bpf_kfunc_call_test_const_struct(const struct prog_test_pass1 *p) __ksym;
 __u64 bpf_kfunc_arena_arg_test(__u64 *val__arena) __ksym;
 __u64 bpf_kfunc_arena_cap_test(__u64 *val__arena) __ksym;
 __u64 bpf_kfunc_arena_cap_nullable_test(__u64 *val__arena__nullable) __ksym;
-- 
2.43.0