From: Alexei Starovoitov <ast@fb.com>
To: Yonghong Song <yhs@fb.com>, Martin KaFai Lau <kafai@fb.com>
Cc: Andrii Nakryiko <andriin@fb.com>, <bpf@vger.kernel.org>,
<netdev@vger.kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
<kernel-team@fb.com>
Subject: Re: [PATCH bpf-next v1 03/19] bpf: add bpf_map iterator
Date: Tue, 28 Apr 2020 19:44:37 -0700 [thread overview]
Message-ID: <65a83b48-3965-5ae9-fafd-3e8836b03d2c@fb.com> (raw)
In-Reply-To: <a5255338-94e8-3f4b-518e-e7f7146f69f2@fb.com>
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.
next prev parent reply other threads:[~2020-04-29 2:44 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 [this message]
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
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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