From: Alexei Starovoitov <ast@fb.com>
To: Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Martin KaFai Lau <kafai@fb.com>, Andrii Nakryiko <andriin@fb.com>,
bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next v1 03/19] bpf: add bpf_map iterator
Date: Tue, 28 Apr 2020 23:30:03 -0700 [thread overview]
Message-ID: <f9a3590f-1fd3-2151-5b52-4e7ddc0da934@fb.com> (raw)
In-Reply-To: <401b5bd2-dc43-4465-1232-34428a1b3e4e@fb.com>
On 4/28/20 11:20 PM, Yonghong Song wrote:
>
>
> On 4/28/20 11:08 PM, Andrii Nakryiko wrote:
>> On Tue, Apr 28, 2020 at 10:10 PM Yonghong Song <yhs@fb.com> wrote:
>>>
>>>
>>>
>>> On 4/28/20 7:44 PM, Alexei Starovoitov wrote:
>>>> On 4/28/20 6:15 PM, Yonghong Song wrote:
>>>>>
>>>>>
>>>>> On 4/28/20 5:48 PM, Alexei Starovoitov wrote:
>>>>>> On 4/28/20 5:37 PM, Martin KaFai Lau wrote:
>>>>>>>> + prog = bpf_iter_get_prog(seq, sizeof(struct
>>>>>>>> bpf_iter_seq_map_info),
>>>>>>>> + &meta.session_id, &meta.seq_num,
>>>>>>>> + v == (void *)0);
>>>>>>> From looking at seq_file.c, when will show() be called with "v ==
>>>>>>> NULL"?
>>>>>>>
>>>>>>
>>>>>> that v == NULL here and the whole verifier change just to allow
>>>>>> NULL...
>>>>>> may be use seq_num as an indicator of the last elem instead?
>>>>>> Like seq_num with upper bit set to indicate that it's last?
>>>>>
>>>>> We could. But then verifier won't have an easy way to verify that.
>>>>> For example, the above is expected:
>>>>>
>>>>> int prog(struct bpf_map *map, u64 seq_num) {
>>>>> if (seq_num >> 63)
>>>>> return 0;
>>>>> ... map->id ...
>>>>> ... map->user_cnt ...
>>>>> }
>>>>>
>>>>> But if user writes
>>>>>
>>>>> int prog(struct bpf_map *map, u64 seq_num) {
>>>>> ... map->id ...
>>>>> ... map->user_cnt ...
>>>>> }
>>>>>
>>>>> verifier won't be easy to conclude inproper map pointer tracing
>>>>> here and in the above map->id, map->user_cnt will cause
>>>>> exceptions and they will silently get value 0.
>>>>
>>>> I mean always pass valid object pointer into the prog.
>>>> In above case 'map' will always be valid.
>>>> Consider prog that iterating all map elements.
>>>> It's weird that the prog would always need to do
>>>> if (map == 0)
>>>> goto out;
>>>> even if it doesn't care about finding last.
>>>> All progs would have to have such extra 'if'.
>>>> If we always pass valid object than there is no need
>>>> for such extra checks inside the prog.
>>>> First and last element can be indicated via seq_num
>>>> or via another flag or via helper call like is_this_last_elem()
>>>> or something.
>>>
>>> Okay, I see what you mean now. Basically this means
>>> seq_ops->next() should try to get/maintain next two elements,
>>
>> What about the case when there are no elements to iterate to begin
>> with? In that case, we still need to call bpf_prog for (empty)
>> post-aggregation, but we have no valid element... For bpf_map
>> iteration we could have fake empty bpf_map that would be passed, but
>> I'm not sure it's applicable for any time of object (e.g., having a
>> fake task_struct is probably quite a bit more problematic?)...
>
> Oh, yes, thanks for reminding me of this. I put a call to
> bpf_prog in seq_ops->stop() especially to handle no object
> case. In that case, seq_ops->start() will return NULL,
> seq_ops->next() won't be called, and then seq_ops->stop()
> is called. My earlier attempt tries to hook with next()
> and then find it not working in all cases.
wait a sec. seq_ops->stop() is not the end.
With lseek of seq_file it can be called multiple times.
What's the point calling bpf prog with NULL then?
next prev parent reply other threads:[~2020-04-29 6:30 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-27 20:12 [PATCH bpf-next v1 00/19] bpf: implement bpf iterator for kernel data Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 01/19] net: refactor net assignment for seq_net_private structure Yonghong Song
2020-04-29 5:38 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 02/19] bpf: implement an interface to register bpf_iter targets Yonghong Song
2020-04-28 16:20 ` Martin KaFai Lau
2020-04-28 16:50 ` Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 03/19] bpf: add bpf_map iterator Yonghong Song
2020-04-29 0:37 ` Martin KaFai Lau
2020-04-29 0:48 ` Alexei Starovoitov
2020-04-29 1:15 ` Yonghong Song
2020-04-29 2:44 ` Alexei Starovoitov
2020-04-29 5:09 ` Yonghong Song
2020-04-29 6:08 ` Andrii Nakryiko
2020-04-29 6:20 ` Yonghong Song
2020-04-29 6:30 ` Alexei Starovoitov [this message]
2020-04-29 6:40 ` Andrii Nakryiko
2020-04-29 6:44 ` Yonghong Song
2020-04-29 15:34 ` Alexei Starovoitov
2020-04-29 18:14 ` Yonghong Song
2020-04-29 19:19 ` Andrii Nakryiko
2020-04-29 20:15 ` Yonghong Song
2020-04-30 3:06 ` Alexei Starovoitov
2020-04-30 4:01 ` Yonghong Song
2020-04-29 6:34 ` Martin KaFai Lau
2020-04-29 6:51 ` Yonghong Song
2020-04-29 19:25 ` Andrii Nakryiko
2020-04-29 1:02 ` Yonghong Song
2020-04-29 6:04 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 04/19] bpf: allow loading of a bpf_iter program Yonghong Song
2020-04-29 0:54 ` Martin KaFai Lau
2020-04-29 1:27 ` Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 05/19] bpf: support bpf tracing/iter programs for BPF_LINK_CREATE Yonghong Song
2020-04-29 1:17 ` [Potential Spoof] " Martin KaFai Lau
2020-04-29 6:25 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 06/19] bpf: support bpf tracing/iter programs for BPF_LINK_UPDATE Yonghong Song
2020-04-29 1:32 ` Martin KaFai Lau
2020-04-29 5:04 ` Yonghong Song
2020-04-29 5:58 ` Martin KaFai Lau
2020-04-29 6:32 ` Andrii Nakryiko
2020-04-29 6:41 ` Martin KaFai Lau
2020-04-27 20:12 ` [PATCH bpf-next v1 07/19] bpf: create anonymous bpf iterator Yonghong Song
2020-04-29 5:39 ` Martin KaFai Lau
2020-04-29 6:56 ` Andrii Nakryiko
2020-04-29 7:06 ` Yonghong Song
2020-04-29 18:16 ` Andrii Nakryiko
2020-04-29 18:46 ` Martin KaFai Lau
2020-04-29 19:20 ` Yonghong Song
2020-04-29 20:50 ` Martin KaFai Lau
2020-04-29 20:54 ` Yonghong Song
2020-04-29 19:39 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 08/19] bpf: create file " Yonghong Song
2020-04-29 20:40 ` Andrii Nakryiko
2020-04-30 18:02 ` Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 09/19] bpf: add PTR_TO_BTF_ID_OR_NULL support Yonghong Song
2020-04-29 20:46 ` Andrii Nakryiko
2020-04-29 20:51 ` Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 10/19] bpf: add netlink and ipv6_route targets Yonghong Song
2020-04-28 19:49 ` kbuild test robot
2020-04-28 19:50 ` [RFC PATCH] bpf: __bpf_iter__netlink() can be static kbuild test robot
2020-04-27 20:12 ` [PATCH bpf-next v1 11/19] bpf: add task and task/file targets Yonghong Song
2020-04-30 2:08 ` Andrii Nakryiko
2020-05-01 17:23 ` Yonghong Song
2020-05-01 19:01 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 12/19] bpf: add bpf_seq_printf and bpf_seq_write helpers Yonghong Song
2020-04-28 6:02 ` kbuild test robot
2020-04-28 16:35 ` Yonghong Song
2020-04-30 20:06 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 13/19] bpf: handle spilled PTR_TO_BTF_ID properly when checking stack_boundary Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 14/19] bpf: support variable length array in tracing programs Yonghong Song
2020-04-30 20:04 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 15/19] tools/libbpf: add bpf_iter support Yonghong Song
2020-04-30 1:41 ` Andrii Nakryiko
2020-05-02 7:17 ` Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 16/19] tools/bpftool: add bpf_iter support for bptool Yonghong Song
2020-04-28 9:27 ` Quentin Monnet
2020-04-28 17:35 ` Yonghong Song
2020-04-29 8:37 ` Quentin Monnet
2020-04-27 20:12 ` [PATCH bpf-next v1 17/19] tools/bpf: selftests: add iterator programs for ipv6_route and netlink Yonghong Song
2020-04-30 2:12 ` Andrii Nakryiko
2020-04-27 20:12 ` [PATCH bpf-next v1 18/19] tools/bpf: selftests: add iter progs for bpf_map/task/task_file Yonghong Song
2020-04-27 20:12 ` [PATCH bpf-next v1 19/19] tools/bpf: selftests: add bpf_iter selftests Yonghong Song
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