[bpf-next,1/2] bpf: Add bpf_task_under_cgroup helper

From: Feng Zhou <zhoufeng.zf@bytedance.com>

This adds a bpf helper that's similar to the
bpf_current_task_under_cgroup. The difference is that it is a
designated task.

When hook sched related functions, sometimes it is necessary to
specify a task instead of the current task.

Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
---
 include/uapi/linux/bpf.h       | 13 +++++++++++++
 kernel/bpf/verifier.c          |  4 +++-
 kernel/trace/bpf_trace.c       | 31 +++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h | 13 +++++++++++++
 4 files changed, 60 insertions(+), 1 deletion(-)

在 2023/4/21 02:22, Alexei Starovoitov 写道:
> On Thu, Apr 20, 2023 at 12:27 AM Feng zhou <zhoufeng.zf@bytedance.com> wrote:
>> From: Feng Zhou <zhoufeng.zf@bytedance.com>
>>
>> This adds a bpf helper that's similar to the
>> bpf_current_task_under_cgroup. The difference is that it is a
>> designated task.
>>
>> When hook sched related functions, sometimes it is necessary to
>> specify a task instead of the current task.
>>
>> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
>> ---
>>   include/uapi/linux/bpf.h       | 13 +++++++++++++
>>   kernel/bpf/verifier.c          |  4 +++-
>>   kernel/trace/bpf_trace.c       | 31 +++++++++++++++++++++++++++++++
>>   tools/include/uapi/linux/bpf.h | 13 +++++++++++++
>>   4 files changed, 60 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 4b20a7269bee..3d31ddb39e10 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -5550,6 +5550,18 @@ union bpf_attr {
>>    *             0 on success.
>>    *
>>    *             **-ENOENT** if the bpf_local_storage cannot be found.
>> + *
>> + * long bpf_task_under_cgroup(struct bpf_map *map, struct task_struct *task, u32 index)
>> + *     Description
>> + *             Check whether the probe is being run is the context of a given
>> + *             subset of the cgroup2 hierarchy. The cgroup2 to test is held by
>> + *             *map* of type **BPF_MAP_TYPE_CGROUP_ARRAY**, at *index*.
>> + *     Return
>> + *             The return value depends on the result of the test, and can be:
>> + *
>> + *             * 1, if assigned task belongs to the cgroup2.
>> + *             * 0, if assigned task does not belong to the cgroup2.
>> + *             * A negative error code, if an error occurred.
>>    */
>>   #define ___BPF_FUNC_MAPPER(FN, ctx...)                 \
>>          FN(unspec, 0, ##ctx)                            \
>> @@ -5764,6 +5776,7 @@ union bpf_attr {
>>          FN(user_ringbuf_drain, 209, ##ctx)              \
>>          FN(cgrp_storage_get, 210, ##ctx)                \
>>          FN(cgrp_storage_delete, 211, ##ctx)             \
>> +       FN(task_under_cgroup, 212, ##ctx)               \
>>          /* */
>>
>>   /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 1e05355facdc..1e2c3c3e8d5f 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -7771,7 +7771,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>>                  break;
>>          case BPF_MAP_TYPE_CGROUP_ARRAY:
>>                  if (func_id != BPF_FUNC_skb_under_cgroup &&
>> -                   func_id != BPF_FUNC_current_task_under_cgroup)
>> +                   func_id != BPF_FUNC_current_task_under_cgroup &&
>> +                   func_id != BPF_FUNC_task_under_cgroup)
>>                          goto error;
>>                  break;
>>          case BPF_MAP_TYPE_CGROUP_STORAGE:
>> @@ -7902,6 +7903,7 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>>                          goto error;
>>                  break;
>>          case BPF_FUNC_current_task_under_cgroup:
>> +       case BPF_FUNC_task_under_cgroup:
>>          case BPF_FUNC_skb_under_cgroup:
>>                  if (map->map_type != BPF_MAP_TYPE_CGROUP_ARRAY)
>>                          goto error;
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index bcf91bc7bf71..b02a04768824 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -814,6 +814,35 @@ static const struct bpf_func_proto bpf_current_task_under_cgroup_proto = {
>>          .arg2_type      = ARG_ANYTHING,
>>   };
>>
>> +BPF_CALL_3(bpf_task_under_cgroup, struct bpf_map *, map, struct task_struct *,
>> +          task, u32, idx)
>> +{
>> +       struct bpf_array *array = container_of(map, struct bpf_array, map);
>> +       struct cgroup *cgrp;
>> +
>> +       if (unlikely(!task))
>> +               return -ENOENT;
>> +
>> +       if (unlikely(idx >= array->map.max_entries))
>> +               return -E2BIG;
>> +
>> +       cgrp = READ_ONCE(array->ptrs[idx]);
>> +       if (unlikely(!cgrp))
>> +               return -EAGAIN;
>> +
>> +       return task_under_cgroup_hierarchy(task, cgrp);
> We don't add helpers anymore.
> Please wrap task_under_cgroup_hierarchy() as a kfunc
> that takes two TRUSTED pointers task and cgroup.
Will do, thanks.