selftests/bpf: Cover trusted BTF ID argument provenance

Extend verifier_global_ptr_args.c with calls that pass bare and
RCU-protected task pointers to a global __arg_trusted parameter. Both
calls must be rejected because neither pointer is referenced or trusted.

Add paired test-module kfuncs that return and accept a nullable trusted
task pointer. Passing the return value directly must succeed, covering
PTR_TRUSTED | PTR_MAYBE_NULL handling in the common argument checker.

Signed-off-by: Yiyang Chen <chenyy23@mails.tsinghua.edu.cn>
Reviewed-by: Amery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/bpf/20261007-a3-arg-trusted-v4-v4-2-253ef3a1a69a@mails.tsinghua.edu.cn
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

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

@@ -46,6 +46,17 @@ int iter_next_trusted_or_null(const void *ctx)
 	return 0;
 }
 
+SEC("syscall")
+__success
+int trusted_nullable_kfunc(const void *ctx)
+{
+	struct task_struct *task;
+
+	task = bpf_kfunc_trusted_null_test();
+	bpf_kfunc_trusted_nullable_test(task);
+	return 0;
+}
+
 SEC("raw_tp/sys_enter")
 __success
 int iter_next_rcu(const void *ctx)

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

@@ -289,6 +289,41 @@ __weak int subprog_void_untrusted(void *p __arg_untrusted)
 	return *(int *)p;
 }
 
+__weak int subprog_trusted_bare(struct task_struct *task __arg_trusted)
+{
+	return task->pid;
+}
+
+SEC("tp_btf/task_newtask")
+__failure
+__msg("R1 must be referenced or trusted")
+__msg("Caller passes invalid args into func#{{.*}} ('subprog_trusted_bare')")
+int bare_to_trusted(void *ctx)
+{
+	struct task_struct *cur = bpf_get_current_task_btf();
+	struct task_struct *wakee;
+
+	if (!cur)
+		return 0;
+	wakee = cur->last_wakee;
+	if (!wakee)
+		return 0;
+	return subprog_trusted_bare(wakee);
+}
+
+SEC("tp_btf/task_newtask")
+__failure
+__msg("R1 must be referenced or trusted")
+__msg("Caller passes invalid args into func#{{.*}}")
+int memrcu_to_trusted(void *ctx)
+{
+	struct task_struct *cur = bpf_get_current_task_btf();
+
+	if (!cur)
+		return 0;
+	return subprog_trusted_task_nullable(cur->real_parent);
+}
+
 __weak int subprog_char_untrusted(char *p __arg_untrusted)
 {
 	return *(int *)p;

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

@@ -350,6 +350,15 @@ __bpf_kfunc void bpf_kfunc_trusted_task_test(struct task_struct *ptr)
 {
 }
 
+__bpf_kfunc struct task_struct *bpf_kfunc_trusted_null_test(void)
+{
+	return NULL;
+}
+
+__bpf_kfunc void bpf_kfunc_trusted_nullable_test(struct task_struct *ptr__nullable)
+{
+}
+
 __bpf_kfunc void bpf_kfunc_trusted_num_test(int *ptr)
 {
 }
@@ -957,6 +966,8 @@ 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_kfunc_trusted_vma_test)
 BTF_ID_FLAGS(func, bpf_kfunc_trusted_task_test)
+BTF_ID_FLAGS(func, bpf_kfunc_trusted_null_test, KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_kfunc_trusted_nullable_test)
 BTF_ID_FLAGS(func, bpf_kfunc_trusted_num_test)
 BTF_ID_FLAGS(func, bpf_kfunc_rcu_task_test, KF_RCU)
 BTF_ID_FLAGS(func, bpf_kfunc_ret_rcu_test, KF_RET_NULL | KF_RCU_PROTECTED)

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

@@ -353,6 +353,8 @@ int bpf_kfunc_st_ops_inc10(struct st_ops_args *args) __ksym;
 
 void bpf_kfunc_trusted_vma_test(struct vm_area_struct *ptr) __ksym;
 void bpf_kfunc_trusted_task_test(struct task_struct *ptr) __ksym;
+struct task_struct *bpf_kfunc_trusted_null_test(void) __ksym;
+void bpf_kfunc_trusted_nullable_test(struct task_struct *ptr__nullable) __ksym;
 void bpf_kfunc_trusted_num_test(int *ptr) __ksym;
 void bpf_kfunc_rcu_task_test(struct task_struct *ptr) __ksym;
 struct task_struct *bpf_kfunc_ret_rcu_test(void) __ksym;