From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6D08C2D0E5 for ; Mon, 30 Mar 2020 13:53:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B4447206CC for ; Mon, 30 Mar 2020 13:53:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="S+aud7CL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728481AbgC3NxM (ORCPT ); Mon, 30 Mar 2020 09:53:12 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:60107 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725268AbgC3NxM (ORCPT ); Mon, 30 Mar 2020 09:53:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585576390; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sfr3Wz8gZlZ4mZJliKB/GXqT+ZcydbsQOHciCQAiptI=; b=S+aud7CLlPCo5qsTPamXXfUsaqb/1wlnINeNE+nS0HeDAh27cRdFUNlsN7k4dinaaCR7VN Ci5ECQajIP8zCACjdQPIsMBh0piP0CqB0sIQYUqqZfboZ5cHZQxTs9ovdRop9Kw8FJCst+ e9+GO1q4UGOk+mCoR2cQqhIQBSDn/AU= Received: from mail-lf1-f70.google.com (mail-lf1-f70.google.com [209.85.167.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-176-PdnwnAksN-uBH1O2DMhiQA-1; Mon, 30 Mar 2020 09:53:06 -0400 X-MC-Unique: PdnwnAksN-uBH1O2DMhiQA-1 Received: by mail-lf1-f70.google.com with SMTP id b16so489179lfb.19 for ; Mon, 30 Mar 2020 06:53:06 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version:content-transfer-encoding; bh=sfr3Wz8gZlZ4mZJliKB/GXqT+ZcydbsQOHciCQAiptI=; b=t1gijxR5qEy1MMRqa1oqwa2NlLSVGhQQdAU5QI6JH6ydjn4O/7exUmaCEywtUswg14 7ohYeTLfORjkG6FwTSmLeCpaO+3QPgvEkE7+poFs1zMwkchTqyrgkmTZ7HrG2Y37ohBi XgDzCfd2KOiPJa9qu7CYoQH9nLEJQ/N0+LQ9b6r/RC1Xi1MU+MoLclTy6ayQnl+E9v1V x4KkyWDZbCapHtB4E/c4mVFpyunbUx9vTI5mFsEbcpGAPIQnWIi3kTMt74xKvF356uDq bwGVSBDoEVXz7VGljk2MdtD685oiBGrN+IG3yzyPj9ABIxD2+puziyLuoaPG3/11jvNz IH7w== X-Gm-Message-State: AGi0Pubp1jXH4uy2cZA4q7Y9hDI+y2wyIO507xfEF0hfvGgxwDRgP4Hg mhc6Y12waRcLQSyytF1yHFBIfZu9AW13+KVWPYpag2pNWn9TtHCWpP6fCgSY7w4/Z5c6DsBDL46 hWFp6Rkfx1YWd X-Received: by 2002:a2e:7c19:: with SMTP id x25mr6730955ljc.253.1585576384897; Mon, 30 Mar 2020 06:53:04 -0700 (PDT) X-Google-Smtp-Source: APiQypK1KlcuJjhO8efN6nW+lV97DOA1p7DFyGNHe4mVWvFV+Fx9stojzIzoLv6oVJ7Y0uSTN3lCJw== X-Received: by 2002:a2e:7c19:: with SMTP id x25mr6730944ljc.253.1585576384568; Mon, 30 Mar 2020 06:53:04 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id o21sm6892952ljg.71.2020.03.30.06.53.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Mar 2020 06:53:03 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id CA79918158B; Mon, 30 Mar 2020 15:53:01 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Andrii Nakryiko Cc: Alexei Starovoitov , John Fastabend , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , "David S. Miller" , Jesper Dangaard Brouer , Lorenz Bauer , Andrey Ignatov , Networking , bpf Subject: Re: [PATCH bpf-next 1/4] xdp: Support specifying expected existing program when attaching XDP In-Reply-To: References: <87tv2e10ly.fsf@toke.dk> <87369wrcyv.fsf@toke.dk> <87pncznvjy.fsf@toke.dk> <20200326195859.u6inotgrm3ubw5bx@ast-mbp> <87imiqm27d.fsf@toke.dk> <20200327230047.ois5esl35s63qorj@ast-mbp> <87lfnll0eh.fsf@toke.dk> <20200328022609.zfupojim7see5cqx@ast-mbp> <87eetcl1e3.fsf@toke.dk> X-Clacks-Overhead: GNU Terry Pratchett Date: Mon, 30 Mar 2020 15:53:01 +0200 Message-ID: <87y2rihruq.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Andrii Nakryiko writes: > On Sat, Mar 28, 2020 at 12:34 PM Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> >> Alexei Starovoitov writes: >> >> > On Sat, Mar 28, 2020 at 02:43:18AM +0100, Toke H=C3=B8iland-J=C3=B8rge= nsen wrote: >> >> >> >> No, I was certainly not planning to use that to teach libxdp to just >> >> nuke any bpf_link it finds attached to an interface. Quite the contra= ry, >> >> the point of this series is to allow libxdp to *avoid* replacing >> >> something on the interface that it didn't put there itself. >> > >> > Exactly! "that it didn't put there itself". >> > How are you going to do that? >> > I really hope you thought it through and came up with magic. >> > Because I tried and couldn't figure out how to do that with IFLA_XDP* >> > Please walk me step by step how do you think it's possible. >> >> I'm inspecting the BPF program itself to make sure it's compatible. >> Specifically, I'm embedding a piece of metadata into the program BTF, >> using Andrii's encoding trick that we also use for defining maps. So >> xdp-dispatcher.c contains this[0]: >> >> __uint(dispatcher_version, XDP_DISPATCHER_VERSION) SEC(XDP_METADATA_SECT= ION); >> >> and libxdp will refuse to touch any program that it finds loaded on an > > But you can't say the same about other XDP applications that do not > use libxdp. So will your library come with a huge warning, e.g.: > > WARNING! ANY XDP APPLICATION YOU INSTALL ON YOUR MACHINE THAT DOESN'T > USE LIBXDP WILL BREAK YOUR FIREWALLS/ROUTERS/OTHER LIBXDP > APPLICATIONS. USE AT YOUR OWN RISK. > > So you install your libxdp-based firewalls and are happy. Then you > decide to install this awesome packet analyzer, which doesn't know > about libxdp yet. Suddenly, you get all packets analyzer, but no more > firewall, until users somehow notices that it's gone. Or firewall > periodically checks that it's still runinng. Both not great, IMO, but > might be acceptable for some users, I guess. But imagine all the > confusion for user, especially if he doesn't give a damn about XDP and > other buzzwords, but only needs a reliable firewall :) Yes, whereas if the firewall is using bpf_link, then the packet analyser will be locked out and can't do its thing. Either way you end up with a broken application; it's just moving the breakage. In the case of firewall vs packet analyser it's probably clear what the right precedence is, but what if it's firewall vs IDS? Or two different firewall-type applications? This is the reason I don't believe the problem bpf_link solves is such a big deal: Since multi-prog is implemented in userspace it *fundamentally requires* applications to coordinate. So all the kernel needs to provide, is a way to help well-behaved applications do this coordination, for which REPLACE_FD is sufficient. Now, this picture changes a bit if you have a more-privileged application managing things - such as the "xdp daemon" I believe you're using, right? In that case it becomes obvious which application should have precedence, and the "lock-out" feature makes sense (assuming you can't just use capabilities to enforce the access restriction). This is why I keep saying that I understand why you want bpf_link for you use case, I just don't think it'll help mine much... :) -Toke