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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Mon, 24 Jan 2022 20:42:52 -0800
Message-ID: <CAADnVQ+MPCmDnyWBP9rm_WDVrDqiTDYSej+ZfN_Z2K_TYYZKnA@mail.gmail.com>
Subject: Re: [PATCH bpf-next 1/1] bpf: Add bpf_copy_from_user_remote to read a
 process VM given its PID.
To:     Gabriele <phoenix1987@gmail.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Yonghong Song <yhs@fb.com>, bpf <bpf@vger.kernel.org>
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On Sun, Jan 23, 2022 at 2:47 AM Gabriele <phoenix1987@gmail.com> wrote:
>
> On Fri, 21 Jan 2022 at 02:09, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > How would bpf prog know the pid of the python interpreter?
> > Then how would it know the pids of the threads?
> > I'm not against exposing find_get_task_by_vpid(), but
> > we need to understand the real usage first.
> > If we do end up exposing find_get_task_by_vpid(), it's probably
> > best to do via refcnt-ed kfunc approach (unstable helpers).
> > For example: https://lore.kernel.org/all/20220114163953.1455836-7-memxor@gmail.com/
>
> This is a simple but somewhat unrealistic example but hopefully it
> will give the idea. Suppose we are tracing sys_kill on entry and that
> we have an application that uses it to check if a process exists by
> sending the 0 signal to its PID. During the handling of this event, we
> might want to read a certain area of the VM (which we would have
> identified a priori from user-space) of the process identified by the
> PID passed to the syscall.

Fair enough. Pls prepare a patch to make find_get_task_by_vpid
into refcnted unstable helper for certain prog types.
Probably sleepable only.