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

thinker.li
2023-08-11T04:31:39Z

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