[RFC bpf-next v2 4/6] bpf: Provide bpf_copy_from_user() and bpf_copy_to_user().

[thinker.li@gmail.com]

From: Kui-Feng Lee <kuifeng@meta.com>

Provide bpf_copy_from_user() and bpf_copy_to_user() to the BPF programs
attached to cgroup/{set,get}sockopt. bpf_copy_to_user() is a new kfunc to
copy data from an kernel space buffer to a user space buffer. They are only
available for sleepable BPF programs. bpf_copy_to_user() is only available
to the BPF programs attached to cgroup/getsockopt.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 kernel/bpf/cgroup.c  |  6 ++++++
 kernel/bpf/helpers.c | 31 +++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 5bf3115b265c..c15a72860d2a 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -2461,6 +2461,12 @@ cg_sockopt_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 #endif
 	case BPF_FUNC_perf_event_output:
 		return &bpf_event_output_data_proto;
+
+	case BPF_FUNC_copy_from_user:
+		if (prog->aux->sleepable)
+			return &bpf_copy_from_user_proto;
+		return NULL;
+
 	default:
 		return bpf_base_func_proto(func_id);
 	}
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index eb91cae0612a..ff240db1512c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -669,6 +669,26 @@ const struct bpf_func_proto bpf_copy_from_user_proto = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
+/**
+ * int bpf_copy_to_user(void *dst, u32 size, const void *kern_ptr)
+ *     Description
+ *             Read *size* bytes from kernel space address *kern_ptr* and
+ *              store the data in user space address *dst*. This is a
+ *              wrapper of **copy_to_user**\ ().
+ *     Return
+ *             0 on success, or a negative error in case of failure.
+ */
+__bpf_kfunc int bpf_copy_to_user(void *dst__uninit, u32 dst__sz,
+				 const void *src__ign)
+{
+	int ret = copy_to_user(dst__uninit, src__ign, dst__sz);
+
+	if (unlikely(ret))
+		return -EFAULT;
+
+	return ret;
+}
+
 BPF_CALL_5(bpf_copy_from_user_task, void *, dst, u32, size,
 	   const void __user *, user_ptr, struct task_struct *, tsk, u64, flags)
 {
@@ -2456,6 +2476,7 @@ BTF_ID_FLAGS(func, bpf_cgroup_from_id, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_under_cgroup, KF_RCU)
 #endif
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_copy_to_user, KF_SLEEPABLE)
 BTF_SET8_END(generic_btf_ids)
 
 static const struct btf_kfunc_id_set generic_kfunc_set = {
@@ -2494,6 +2515,15 @@ static const struct btf_kfunc_id_set common_kfunc_set = {
 	.set   = &common_btf_ids,
 };
 
+BTF_SET8_START(cgroup_common_btf_ids)
+BTF_ID_FLAGS(func, bpf_copy_to_user, KF_SLEEPABLE)
+BTF_SET8_END(cgroup_common_btf_ids)
+
+static const struct btf_kfunc_id_set cgroup_kfunc_set = {
+	.owner	= THIS_MODULE,
+	.set	= &cgroup_common_btf_ids,
+};
+
 static int __init kfunc_init(void)
 {
 	int ret;
@@ -2513,6 +2543,7 @@ static int __init kfunc_init(void)
 	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &generic_kfunc_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &generic_kfunc_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &generic_kfunc_set);
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCKOPT, &cgroup_kfunc_set);
 	ret = ret ?: register_btf_id_dtor_kfuncs(generic_dtors,
 						  ARRAY_SIZE(generic_dtors),
 						  THIS_MODULE);
-- 
2.34.1