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Date: Wed, 3 Nov 2021 23:30:34 -0700
From: Yonghong Song <yhs@...com>
To: "zhudi (E)" <zhudi2@...wei.com>,
"davem@...emloft.net" <davem@...emloft.net>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>,
"andrii@...nel.org" <andrii@...nel.org>,
"kafai@...com" <kafai@...com>,
"songliubraving@...com" <songliubraving@...com>,
"john.fastabend@...il.com" <john.fastabend@...il.com>,
"kpsingh@...nel.org" <kpsingh@...nel.org>,
"jakub@...udflare.com" <jakub@...udflare.com>
CC: "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 1/2] bpf: support BPF_PROG_QUERY for progs
attached to sockmap
On 11/3/21 11:07 PM, zhudi (E) wrote:
> > On 11/3/21 6:07 PM, Di Zhu wrote:
>>> Right now there is no way to query whether BPF programs are
>>> attached to a sockmap or not.
>>>
>>> we can use the standard interface in libbpf to query, such as:
>>> bpf_prog_query(mapFd, BPF_SK_SKB_STREAM_PARSER, 0, NULL, ...);
>>> the mapFd is the fd of sockmap.
>>>
>>> Signed-off-by: Di Zhu <zhudi2@...wei.com>
>>> ---
>>> /* v2 */
>>> - John Fastabend <john.fastabend@...il.com>
>>> - add selftest code
>>>
>>> /* v3 */
>>> - avoid sleeping caused by copy_to_user() in rcu critical zone
>>>
>>> /* v4 */
>>> - Alexei Starovoitov <alexei.starovoitov@...il.com>
>>> -split into two patches, one for core code and one for selftest.
>>>
>>> /* v5 */
>>> - Yonghong Song <yhs@...com>
>>> -Some naming and formatting changes
>>> ---
>>> include/linux/bpf.h | 9 ++++++
>>> kernel/bpf/syscall.c | 5 +++
>>> net/core/sock_map.c | 74
>> +++++++++++++++++++++++++++++++++++++++-----
>>> 3 files changed, 81 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>>> index d604c8251d88..235ea7fc5fd8 100644
>>> --- a/include/linux/bpf.h
>>> +++ b/include/linux/bpf.h
>>> @@ -1961,6 +1961,9 @@ int bpf_prog_test_run_syscall(struct bpf_prog
>> *prog,
>>> int sock_map_get_from_fd(const union bpf_attr *attr, struct bpf_prog
>> *prog);
>>> int sock_map_prog_detach(const union bpf_attr *attr, enum bpf_prog_type
>> ptype);
>>> int sock_map_update_elem_sys(struct bpf_map *map, void *key, void
>> *value, u64 flags);
>>> +int sock_map_bpf_prog_query(const union bpf_attr *attr,
>>> + union bpf_attr __user *uattr);
>>> +
>>> void sock_map_unhash(struct sock *sk);
>>> void sock_map_close(struct sock *sk, long timeout);
>>> #else
>>> @@ -2014,6 +2017,12 @@ static inline int sock_map_update_elem_sys(struct
>> bpf_map *map, void *key, void
>>> {
>>> return -EOPNOTSUPP;
>>> }
>>> +
>>> +static inline int sock_map_bpf_prog_query(const union bpf_attr *attr,
>>> + union bpf_attr __user *uattr)
>>> +{
>>> + return -EINVAL;
>>> +}
>>> #endif /* CONFIG_BPF_SYSCALL */
>>> #endif /* CONFIG_NET && CONFIG_BPF_SYSCALL */
>>>
>>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>>> index 4e50c0bfdb7d..748102c3e0c9 100644
>>> --- a/kernel/bpf/syscall.c
>>> +++ b/kernel/bpf/syscall.c
>>> @@ -3275,6 +3275,11 @@ static int bpf_prog_query(const union bpf_attr
>> *attr,
>>> case BPF_FLOW_DISSECTOR:
>>> case BPF_SK_LOOKUP:
>>> return netns_bpf_prog_query(attr, uattr);
>>> + case BPF_SK_SKB_STREAM_PARSER:
>>> + case BPF_SK_SKB_STREAM_VERDICT:
>>> + case BPF_SK_MSG_VERDICT:
>>> + case BPF_SK_SKB_VERDICT:
>>> + return sock_map_bpf_prog_query(attr, uattr);
>>> default:
>>> return -EINVAL;
>>> }
>>> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>>> index e252b8ec2b85..0320d27550fe 100644
>>> --- a/net/core/sock_map.c
>>> +++ b/net/core/sock_map.c
>>> @@ -1412,38 +1412,50 @@ static struct sk_psock_progs
>> *sock_map_progs(struct bpf_map *map)
>>> return NULL;
>>> }
>>>
>>> -static int sock_map_prog_update(struct bpf_map *map, struct bpf_prog
>> *prog,
>>> - struct bpf_prog *old, u32 which)
>>> +static int sock_map_prog_lookup(struct bpf_map *map, struct bpf_prog
>> ***pprog,
>>> + u32 which)
>>> {
>>> struct sk_psock_progs *progs = sock_map_progs(map);
>>> - struct bpf_prog **pprog;
>>>
>>> if (!progs)
>>> return -EOPNOTSUPP;
>>>
>>> switch (which) {
>>> case BPF_SK_MSG_VERDICT:
>>> - pprog = &progs->msg_parser;
>>> + *pprog = &progs->msg_parser;
>>> break;
>>> #if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
>>> case BPF_SK_SKB_STREAM_PARSER:
>>> - pprog = &progs->stream_parser;
>>> + *pprog = &progs->stream_parser;
>>> break;
>>> #endif
>>> case BPF_SK_SKB_STREAM_VERDICT:
>>> if (progs->skb_verdict)
>>> return -EBUSY;
>>> - pprog = &progs->stream_verdict;
>>> + *pprog = &progs->stream_verdict;
>>> break;
>>> case BPF_SK_SKB_VERDICT:
>>> if (progs->stream_verdict)
>>> return -EBUSY;
>>> - pprog = &progs->skb_verdict;
>>> + *pprog = &progs->skb_verdict;
>>> break;
>>> default:
>>> return -EOPNOTSUPP;
>>> }
>>>
>>> + return 0;
>>> +}
>>> +
>>> +static int sock_map_prog_update(struct bpf_map *map, struct bpf_prog
>> *prog,
>>> + struct bpf_prog *old, u32 which)
>>> +{
>>> + struct bpf_prog **pprog;
>>> + int ret;
>>> +
>>> + ret = sock_map_prog_lookup(map, &pprog, which);
>>> + if (ret)
>>> + return ret;
>>> +
>>> if (old)
>>> return psock_replace_prog(pprog, prog, old);
>>>
>>> @@ -1451,6 +1463,54 @@ static int sock_map_prog_update(struct bpf_map
>> *map, struct bpf_prog *prog,
>>> return 0;
>>> }
>>>
>>> +int sock_map_bpf_prog_query(const union bpf_attr *attr,
>>> + union bpf_attr __user *uattr)
>>> +{
>>> + __u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
>>> + u32 prog_cnt = 0, flags = 0, ufd = attr->target_fd;
>>> + struct bpf_prog **pprog;
>>> + struct bpf_prog *prog;
>>> + struct bpf_map *map;
>>> + struct fd f;
>>> + u32 id = 0;
>>
>> There is no need to initialize 'id = 0'. id will be assigned later.
>
>
> if (!attr->query.prog_cnt || !prog_ids || !prog_cnt) is met, the id will not be assigned later.
> At the end of the function, we judge whether to copy the program ID by the value of the id.
Ya, that is true. id = 0 is indeed needed.
>
>
>>
>>> + int ret;
>>> +
>>> + if (attr->query.query_flags)
>>> + return -EINVAL;
>>> +
>>> + f = fdget(ufd);
>>> + map = __bpf_map_get(f);
>>> + if (IS_ERR(map))
>>> + return PTR_ERR(map);
>>> +
>>> + rcu_read_lock();
>>> +
>>> + ret = sock_map_prog_lookup(map, &pprog, attr->query.attach_type);
>>> + if (ret)
>>> + goto end;
>>> +
>>> + prog = *pprog;
>>> + prog_cnt = (!prog) ? 0 : 1;
>>
>> (!prog) => !prog ?
>
> Yes, It's just my habit
>
>>
>>> +
>>> + if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
>>> + goto end;
>>> +
>>> + id = prog->aux->id;
>>> + if (id == 0)
>>> + prog_cnt = 0;
>>
>>
>> id will never be 0, see function bpf_prog_alloc_id() is syscall.c.
>> So 'if (id == 0)' check is not needed.
>
>
> Because we do not hold the reference count, the program may be released synchronously
synchronously => asynchronously
> and its ID will be set to 0 in bpf_prog_free_id().
>
> Is that right?
Just checked the code again. You are right. Maybe add a comment here to
make it clear why we check id == 0 here?
>
>
>>
>>> +
>>> +end:
>>> + rcu_read_unlock();
>>> +
>>> + if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)) ||
>>> + (id != 0 && copy_to_user(prog_ids, &id, sizeof(u32))) ||
>>> + copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))
>>> + ret = -EFAULT;
>>> +
>>> + fdput(f);
>>> + return ret;
>>> +}
>>> +
>>> static void sock_map_unlink(struct sock *sk, struct sk_psock_link *link)
>>> {
>>> switch (link->map->map_type) {
>>>
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