From patchwork Sun Aug 2 22:29:46 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexei Starovoitov X-Patchwork-Id: 262816 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=-7.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT 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 64950C433E0 for ; Sun, 2 Aug 2020 22:29:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D1B4206F6 for ; Sun, 2 Aug 2020 22:29:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hcP8Vr1L" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726890AbgHBW3y (ORCPT ); Sun, 2 Aug 2020 18:29:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54918 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726364AbgHBW3x (ORCPT ); Sun, 2 Aug 2020 18:29:53 -0400 Received: from mail-pg1-x541.google.com (mail-pg1-x541.google.com [IPv6:2607:f8b0:4864:20::541]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95843C06174A; Sun, 2 Aug 2020 15:29:53 -0700 (PDT) Received: by mail-pg1-x541.google.com with SMTP id s15so7311005pgc.8; Sun, 02 Aug 2020 15:29:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=2YEGHQC4jdKKr/EU6iElIwGcMsdA5Y6VLblw4x+K/WQ=; b=hcP8Vr1LtqO0rqC0/Vx4p6QOxUOrNZMTW1XW9UtTMzwKLPPhbCcMHKieAy9ZBXXVkq sjjH2WujsAJKEElBYzw2cEezIcE1iPyLYY4hbxOxez5TRDZIb32UqyhbaAlB8sYJpBgv KPIubhlWk9LUMAQn7PORTeXsjOTE/3he2teRxLab68XKZNWAEDn4CgtDdj5qfJbSCQCt vGJlk5h/wR1rnq1KcDLIfyOT+yccc93RWcfdt0AdTqzn3rPW2b+Z7dd9h6FzvZUZWSbg riCzr9HGhqdxt5b04P7k+k7bKmHtVFvaCscvviEkNXsmUyS+9fx7WZ2BbKM+beHUqcQ1 FCdQ== 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:date:message-id; bh=2YEGHQC4jdKKr/EU6iElIwGcMsdA5Y6VLblw4x+K/WQ=; b=ao1d4KLG4DH2ZZ3P0pJ4BhvldTPrdwyz9aa2FJAc0xogo+LDwVJQt3osbsVaESAfEr A6NQlkNj/T+tF9CeSD/txcNHB/XidFap4yenbXngMpZjfp4o3ofuKX0vO1wFaMoYvPUc LNkfYf0CHNFbiTt/c6DKVceouB+tylnZcJwhRCwDF0/aIEFteuIp2lgJFEn8WyMLdk3g kLHcdYb3o2m251NurTk40Tgr7cDv4ivaT+qlcdo6xprICDpVxch9qxHpTdKZCmEUXgph A1k0v1MnaICD7G13w9ZrXxB3tmeT3NDIpiv2s/rMTZv7Gex8DMeyn4zyP3DJUpg2kbc6 uLQA== X-Gm-Message-State: AOAM532aEpD6EhG4/gCMMlKWl2STkZMtsFtvD05lEbyL10T0JahYlbxe TskqL5LYqIUkrX24I4wU63I= X-Google-Smtp-Source: ABdhPJw81mpZTVjC3m7wzg+FpF226YkPQjHBbO9ZLlHZBxw6rWRKXBXzKW8BFXd230DTS+ppVVh5iw== X-Received: by 2002:a62:7a42:: with SMTP id v63mr1679053pfc.313.1596407392989; Sun, 02 Aug 2020 15:29:52 -0700 (PDT) Received: from ast-mbp.thefacebook.com ([163.114.132.7]) by smtp.gmail.com with ESMTPSA id g5sm15544414pjl.31.2020.08.02.15.29.51 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 02 Aug 2020 15:29:52 -0700 (PDT) From: Alexei Starovoitov To: davem@davemloft.net Cc: daniel@iogearbox.net, netdev@vger.kernel.org, bpf@vger.kernel.org, kernel-team@fb.com Subject: [PATCH v5 bpf-next 0/4] bpf: Populate bpffs with map and prog iterators Date: Sun, 2 Aug 2020 15:29:46 -0700 Message-Id: <20200802222950.34696-1-alexei.starovoitov@gmail.com> X-Mailer: git-send-email 2.13.5 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Alexei Starovoitov v4->v5: - addressed Song and Andrii feedback. s/pages/max_entries/ v3->v4: - took THIS_MODULE in patch 3 as suggested by Daniel to simplify the code. - converted BPF iterator to use BTF (when available) to print full BPF program name instead of 16-byte truncated version. This is something I've been using drgn scripts for. Take a look at get_name() in iterators.bpf.c to see how short it is comparing to what user space bpftool would have to do to print the same full name: . get prog info via obj_info_by_fd . do get_fd_by_id from info->btf_id . fetch potentially large BTF of the program from the kernel . parse that BTF in user space to figure out all type boundaries and string section . read info->func_info to get btf_id of func_proto from there . find that btf_id in the parsed BTF That's quite a bit work for bpftool comparing to few lines in get_name(). I guess would be good to make bpftool do this info extraction anyway. While doing this BTF reading in the kernel realized that the verifier is not smart enough to follow double pointers (added to my todo list), otherwise get_name() would have been even shorter. v2->v3: - fixed module unload race (Daniel) - added selftest (Daniel) - fixed build bot warning v1->v2: - changed names to 'progs.debug' and 'maps.debug' to hopefully better indicate instability of the text output. Having dot in the name also guarantees that these special files will not conflict with normal bpf objects pinned in bpffs, since dot is disallowed for normal pins. - instead of hard coding link_name in the core bpf moved into UMD. - cleanedup error handling. - addressed review comments from Yonghong and Andrii. This patch set is the first real user of user moder driver facility. The general use case for user mode driver is to ship vmlinux with preloaded BPF programs. In this particular case the user mode driver populates bpffs instance with two BPF iterators. In several months BPF_LSM project would need to preload the kernel with its own set of BPF programs and attach to LSM hooks instead of bpffs. BPF iterators and BPF_LSM are unstable from uapi perspective. They are tracing based and peek into arbitrary kernel data structures. One can question why a kernel module cannot embed BPF programs inside. The reason is that libbpf is necessary to load them. First libbpf loads BPF Type Format, then creates BPF maps, populates them. Then it relocates code sections inside BPF programs, loads BPF programs, and finally attaches them to events. Theoretically libbpf can be rewritten to work in the kernel, but that is massive undertaking. The maintenance of in-kernel libbpf and user space libbpf would be another challenge. Another obstacle to embedding BPF programs into kernel module is sys_bpf api. Loading of programs, BTF, maps goes through the verifier. It validates and optimizes the code. It's possible to provide in-kernel api to all of sys_bpf commands (load progs, create maps, update maps, load BTF, etc), but that is huge amount of work and forever maintenance headache. Hence the decision is to ship vmlinux with user mode drivers that load BPF programs. Just like kernel modules extend vmlinux BPF programs are safe extensions of the kernel and some of them need to ship with vmlinux. This patch set adds a kernel module with user mode driver that populates bpffs with two BPF iterators. $ mount bpffs /my/bpffs/ -t bpf $ ls -la /my/bpffs/ total 4 drwxrwxrwt 2 root root 0 Jul 2 00:27 . drwxr-xr-x 19 root root 4096 Jul 2 00:09 .. -rw------- 1 root root 0 Jul 2 00:27 maps.debug -rw------- 1 root root 0 Jul 2 00:27 progs.debug The user mode driver will load BPF Type Formats, create BPF maps, populate BPF maps, load two BPF programs, attach them to BPF iterators, and finally send two bpf_link IDs back to the kernel. The kernel will pin two bpf_links into newly mounted bpffs instance under names "progs.debug" and "maps.debug". These two files become human readable. $ cat /my/bpffs/progs.debug id name attached 11 dump_bpf_map bpf_iter_bpf_map 12 dump_bpf_prog bpf_iter_bpf_prog 27 test_pkt_access 32 test_main test_pkt_access test_pkt_access 33 test_subprog1 test_pkt_access_subprog1 test_pkt_access 34 test_subprog2 test_pkt_access_subprog2 test_pkt_access 35 test_subprog3 test_pkt_access_subprog3 test_pkt_access 36 new_get_skb_len get_skb_len test_pkt_access 37 new_get_skb_ifindex get_skb_ifindex test_pkt_access 38 new_get_constant get_constant test_pkt_access The BPF program dump_bpf_prog() in iterators.bpf.c is printing this data about all BPF programs currently loaded in the system. This information is unstable and will change from kernel to kernel. In some sence this output is similar to 'bpftool prog show' that is using stable api to retreive information about BPF programs. The BPF subsytems grows quickly and there is always demand to show as much info about BPF things as possible. But we cannot expose all that info via stable uapi of bpf syscall, since the details change so much. Right now a BPF program can be attached to only one other BPF program. Folks are working on patches to enable multi-attach, but for debugging it's necessary to see the current state. There is no uapi for that, but above output shows it: 37 new_get_skb_ifindex get_skb_ifindex test_pkt_access 38 new_get_constant get_constant test_pkt_access [1] [2] [3] [1] is the full name of BPF prog from BTF. [2] is the name of function inside target BPF prog. [3] is the name of target BPF prog. [2] and [3] are not exposed via uapi, since they will change from single to multi soon. There are many other cases where bpf internals are useful for debugging, but shouldn't be exposed via uapi due to high rate of changes. systemd mounts /sys/fs/bpf at the start, so this kernel module with user mode driver needs to be available early. BPF_LSM most likely would need to preload BPF programs even earlier. Few interesting observations: - though bpffs comes with two human readble files "progs.debug" and "maps.debug" they can be removed. 'rm -f /sys/fs/bpf/progs.debug' will remove bpf_link and kernel will automatically unload corresponding BPF progs, maps, BTFs. In the future '-o remount' will be able to restore them. This is not implemented yet. - 'ps aux|grep bpf_preload' shows nothing. User mode driver loaded BPF iterators and exited. Nothing is lingering in user space at this point. - We can consider giving 0644 permissions to "progs.debug" and "maps.debug" to allow unprivileged users see BPF things loaded in the system. We cannot do so with "bpftool prog show", since it's using cap_sys_admin parts of bpf syscall. - The functionality split between core kernel, bpf_preload kernel module and user mode driver is very similar to bpfilter style of interaction. - Similar BPF iterators can be used as unstable extensions to /proc. Like mounting /proc can prepopolate some subdirectory in there with a BPF iterator that will print QUIC sockets instead of tcp and udp. Alexei Starovoitov (4): bpf: Factor out bpf_link_by_id() helper. bpf: Add BPF program and map iterators as built-in BPF programs. bpf: Add kernel module with user mode driver that populates bpffs. selftests/bpf: Add bpffs preload test. include/linux/bpf.h | 1 + init/Kconfig | 2 + kernel/bpf/Makefile | 1 + kernel/bpf/inode.c | 116 ++++- kernel/bpf/preload/Kconfig | 18 + kernel/bpf/preload/Makefile | 21 + kernel/bpf/preload/bpf_preload.h | 16 + kernel/bpf/preload/bpf_preload_kern.c | 91 ++++ kernel/bpf/preload/bpf_preload_umd_blob.S | 7 + kernel/bpf/preload/iterators/.gitignore | 2 + kernel/bpf/preload/iterators/Makefile | 57 +++ kernel/bpf/preload/iterators/README | 4 + .../preload/iterators/bpf_preload_common.h | 13 + kernel/bpf/preload/iterators/iterators.bpf.c | 114 +++++ kernel/bpf/preload/iterators/iterators.c | 94 ++++ kernel/bpf/preload/iterators/iterators.skel.h | 410 ++++++++++++++++++ kernel/bpf/syscall.c | 46 +- .../selftests/bpf/prog_tests/test_bpffs.c | 94 ++++ 18 files changed, 1086 insertions(+), 21 deletions(-) create mode 100644 kernel/bpf/preload/Kconfig create mode 100644 kernel/bpf/preload/Makefile create mode 100644 kernel/bpf/preload/bpf_preload.h create mode 100644 kernel/bpf/preload/bpf_preload_kern.c create mode 100644 kernel/bpf/preload/bpf_preload_umd_blob.S create mode 100644 kernel/bpf/preload/iterators/.gitignore create mode 100644 kernel/bpf/preload/iterators/Makefile create mode 100644 kernel/bpf/preload/iterators/README create mode 100644 kernel/bpf/preload/iterators/bpf_preload_common.h create mode 100644 kernel/bpf/preload/iterators/iterators.bpf.c create mode 100644 kernel/bpf/preload/iterators/iterators.c create mode 100644 kernel/bpf/preload/iterators/iterators.skel.h create mode 100644 tools/testing/selftests/bpf/prog_tests/test_bpffs.c