linux-kernel - Re: [PATCH bpf-next v5 4/5] bpf: Make fs kfuncs available for SYSCALL and TRACING program types

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Message-ID:
 <DB7PR03MB5081B6DC951ED1776640939199382@DB7PR03MB5081.eurprd03.prod.outlook.com>
Date: Fri, 13 Dec 2024 18:44:00 +0000
From: Juntong Deng <juntong.deng@...look.com>
To: Song Liu <song@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Christian Brauner <brauner@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>,
 Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>,
 snorcht@...il.com, bpf <bpf@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>,
 Linux-Fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 4/5] bpf: Make fs kfuncs available for SYSCALL
 and TRACING program types

On 2024/12/11 22:06, Song Liu wrote:
> On Wed, Dec 11, 2024 at 1:29 PM Juntong Deng <juntong.deng@...look.com> wrote:
>>
>> On 2024/12/10 18:58, Alexei Starovoitov wrote:
>>> On Tue, Dec 10, 2024 at 6:43 AM Christian Brauner <brauner@...nel.org> wrote:
>>>>
>>>> On Tue, Dec 10, 2024 at 02:03:53PM +0000, Juntong Deng wrote:
>>>>> Currently fs kfuncs are only available for LSM program type, but fs
>>>>> kfuncs are generic and useful for scenarios other than LSM.
>>>>>
>>>>> This patch makes fs kfuncs available for SYSCALL and TRACING
>>>>> program types.
>>>>
>>>> I would like a detailed explanation from the maintainers what it means
>>>> to make this available to SYSCALL program types, please.
>>>
>>> Sigh.
>>> This is obviously not safe from tracing progs.
>>>
>>>   From BPF_PROG_TYPE_SYSCALL these kfuncs should be safe to use,
>>> since those progs are not attached to anything.
>>> Such progs can only be executed via sys_bpf syscall prog_run command.
>>> They're sleepable, preemptable, faultable, in task ctx.
>>>
>>> But I'm not sure what's the value of enabling these kfuncs for
>>> BPF_PROG_TYPE_SYSCALL.
>>
>> Thanks for your reply.
>>
>> Song said here that we need some of these kfuncs to be available for
>> tracing functions [0].
> 
> I meant we can put the new kfuncs, such as bpf_get_file_ops_type, in
> bpf_fs_kfuncs.c, and make it available to tracing programs. But we
> cannot blindly make all of these kfuncs available to tracing programs.
> Instead, we need to review each kfunc and check whether it is safe
> for tracing programs.
> 
> Thanks,
> Song
> 

Thanks for joining the discussion.

Yes, we should do that.

Sorry for the misunderstanding.

>> If Song saw this email, could you please join the discussion?
>>
>> [0]:
>> https://lore.kernel.org/bpf/CAPhsuW6ud21v2xz8iSXf=CiDL+R_zpQ+p8isSTMTw=EiJQtRSw@mail.gmail.com/