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=-5.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 E5E04C3A589 for ; Thu, 15 Aug 2019 20:17:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ABC932086C for ; Thu, 15 Aug 2019 20:17:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="SO6Tvy4C" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731328AbfHOURB (ORCPT ); Thu, 15 Aug 2019 16:17:01 -0400 Received: from mail-io1-f68.google.com ([209.85.166.68]:35606 "EHLO mail-io1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726370AbfHOURB (ORCPT ); Thu, 15 Aug 2019 16:17:01 -0400 Received: by mail-io1-f68.google.com with SMTP id i22so1727778ioh.2 for ; Thu, 15 Aug 2019 13:17:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=RzfaHuwhDPX68hBxarqniibN5HOn+nFygAl5ItvTjGo=; b=SO6Tvy4CDBkNn+chm2JQTQxZWZsAQJe7GproB/4MNL+bM9UY8ZBWMJzJKsyTh4Z6KI WR1fKoTpa3rsg3cDPBvn/tcvA7/zfMKgpu1++tXzyhlaqijlzIOX5vchXei0Zk51sRSS IV1O1Lm2uEmv7c7hg5VIwMpvC1btPtU6RDEuftJND0uEHbRbs+EUqzxyHdLhltNWa7sn 92LvT5dVeU8mQDW3o+TPipx2NH5TRX3OLca71i956lUH6JKOd7USj0DvJM9+nxvOWABv kc2pomYHtXHuFFzrXuFWZWfLmeILmvY/kjGfUaUsDNPWDXkUaYT/dRUKvr2H8Kkwf85A nf4g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=RzfaHuwhDPX68hBxarqniibN5HOn+nFygAl5ItvTjGo=; b=M8w5I0l/D9BS7+9Msaru9pGMKaGybs4Sxk5k6+icb7qH9sVUxxy8RrlF2E2U06/3kM vKJcSCCqXXenfLevC9o1ibT2YVru3DLtZLL0/2Ijf+BvpvPh2A5HfrqmVLh2f1xoYXeY juJKa36NvsbT93TmfY5XmbuFghylJDR7jZzTNz7LAaeoaFoTBbK+rdhJyq5He2GKor2j OBYuuOx2ZL4OXQKNs0MPeKgTz19c110hAIMqbbLkPsiyA8A4ORwZ0a71kqbjSEY86BEP LiMhY+OkiL3NuzgoduGWYPfjefMR3N/0Jx+5AW6v7eLn/OcPlxZdBHaO+Yiw/CRkg537 bJmA== X-Gm-Message-State: APjAAAWs7XllFwylJUUQJgC37O5zRZPaTVzFWqlByLyDfg00VVcFpuMC MZ0cSy3YgBsiraztne7oPMR7YpqKbtaRQfhDgHOtUw== X-Google-Smtp-Source: APXvYqxeQrXgCvtXAIKSRlNVokN3zDssxy0pudwbzeKJzc03KH/+EFkQ4pr9nG+ubvO0IBnaLvhbl1LtDi9pEmvOJJ8= X-Received: by 2002:a05:6638:517:: with SMTP id i23mr505221jar.71.1565900219755; Thu, 15 Aug 2019 13:16:59 -0700 (PDT) MIME-Version: 1.0 References: <291d2cda6ee75b4cd4c9ce717c177db18bf03a31.1565188228.git.ilubashe@akamai.com> <20190814184814.GM9280@kernel.org> <20190814185213.GN9280@kernel.org> <23f7b8c7616a467c93ee2c77e8ffd3cf@usma1ex-dag1mb6.msg.corp.akamai.com> In-Reply-To: <23f7b8c7616a467c93ee2c77e8ffd3cf@usma1ex-dag1mb6.msg.corp.akamai.com> From: Mathieu Poirier Date: Thu, 15 Aug 2019 14:16:48 -0600 Message-ID: Subject: Re: [PATCH v3 3/4] perf: Use CAP_SYSLOG with kptr_restrict checks To: "Lubashev, Igor" Cc: Arnaldo Carvalho de Melo , Linux Kernel Mailing List , Jiri Olsa , Alexey Budankov , Peter Zijlstra , Ingo Molnar , Alexander Shishkin , Namhyung Kim , Suzuki K Poulose , linux-arm-kernel , James Morris , Leo Yan Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 14 Aug 2019 at 14:02, Lubashev, Igor wrote: > > > On Wed, August 14, 2019 at 2:52 PM Arnaldo Carvalho de Melo wrote: > > Em Wed, Aug 14, 2019 at 03:48:14PM -0300, Arnaldo Carvalho de Melo > > escreveu: > > > Em Wed, Aug 14, 2019 at 12:04:33PM -0600, Mathieu Poirier escreveu: > > > > # echo 0 > /proc/sys/kernel/kptr_restrict # ./tools/perf/perf record > > > > -e instructions:k uname > > > > perf: Segmentation fault > > > > Obtained 10 stack frames. > > > > ./tools/perf/perf(sighandler_dump_stack+0x44) [0x55af9e5da5d4] > > > > /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20) [0x7fd31efb6f20] > > > > ./tools/perf/perf(perf_event__synthesize_kernel_mmap+0xa7) > > > > [0x55af9e590337] > > > > ./tools/perf/perf(+0x1cf5be) [0x55af9e50c5be] > > > > ./tools/perf/perf(cmd_record+0x1022) [0x55af9e50dff2] > > > > ./tools/perf/perf(+0x23f98d) [0x55af9e57c98d] > > > > ./tools/perf/perf(+0x23fc9e) [0x55af9e57cc9e] > > > > ./tools/perf/perf(main+0x369) [0x55af9e4f6bc9] > > > > /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) > > > > [0x7fd31ef99b97] > > > > ./tools/perf/perf(_start+0x2a) [0x55af9e4f704a] Segmentation fault > > > > > > > > I can reproduce this on both x86 and ARM64. > > > > > > I don't see this with these two csets removed: > > > > > > 7ff5b5911144 perf symbols: Use CAP_SYSLOG with kptr_restrict checks > > > d7604b66102e perf tools: Use CAP_SYS_ADMIN with perf_event_paranoid > > > checks > > > > > > Which were the ones I guessed were related to the problem you > > > reported, so they are out of my ongoing perf/core pull request to > > > Ingo/Thomas, now trying with these applied and your instructions... > > > > Can't repro: > > > > [root@quaco ~]# cat /proc/sys/kernel/kptr_restrict > > 0 > > [root@quaco ~]# perf record -e instructions:k uname Linux [ perf record: > > Woken up 1 times to write data ] [ perf record: Captured and wrote 0.024 MB > > perf.data (1 samples) ] [root@quaco ~]# echo 1 > > > /proc/sys/kernel/kptr_restrict [root@quaco ~]# perf record -e instructions:k > > uname Linux [ perf record: Woken up 1 times to write data ] [ perf record: > > Captured and wrote 0.024 MB perf.data (1 samples) ] [root@quaco ~]# echo > > 0 > /proc/sys/kernel/kptr_restrict [root@quaco ~]# perf record -e > > instructions:k uname Linux [ perf record: Woken up 1 times to write data ] [ > > perf record: Captured and wrote 0.024 MB perf.data (1 samples) ] > > [root@quaco ~]# > > > > [acme@quaco perf]$ git log --oneline --author Lubashev tools/ > > 7ff5b5911144 (HEAD -> perf/cap, acme.korg/tmp.perf/cap, > > acme.korg/perf/cap) perf symbols: Use CAP_SYSLOG with kptr_restrict > > checks d7604b66102e perf tools: Use CAP_SYS_ADMIN with > > perf_event_paranoid checks c766f3df635d perf ftrace: Use CAP_SYS_ADMIN > > instead of euid==0 c22e150e3afa perf tools: Add helpers to use capabilities if > > present > > 74d5f3d06f70 tools build: Add capability-related feature detection perf > > version 5.3.rc4.g7ff5b5911144 [acme@quaco perf]$ > > I got an ARM64 cloud VM, but I cannot reproduce. > # cat /proc/sys/kernel/kptr_restrict > 0 > > Perf trace works fine (does not die): > # ./perf trace -a > > Here is my setup: > Repo: git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git > Branch: tmp.perf/cap > Commit: 7ff5b5911 "perf symbols: Use CAP_SYSLOG with kptr_restrict checks" > gcc --version: gcc (Ubuntu/Linaro 7.4.0-1ubuntu1~18.04.1) 7.4.0 > uname -a: Linux arm-4-par-1 4.9.93-mainline-rev1 #1 SMP Tue Apr 10 09:54:46 UTC 2018 aarch64 aarch64 aarch64 GNU/Linux > lsb_release -a: Ubuntu 18.04.3 LTS > > Auto-detecting system features: > ... dwarf: [ on ] > ... dwarf_getlocations: [ on ] > ... glibc: [ on ] > ... gtk2: [ on ] > ... libaudit: [ on ] > ... libbfd: [ on ] > ... libcap: [ on ] > ... libelf: [ on ] > ... libnuma: [ on ] > ... numa_num_possible_cpus: [ on ] > ... libperl: [ on ] > ... libpython: [ on ] > ... libcrypto: [ on ] > ... libunwind: [ on ] > ... libdw-dwarf-unwind: [ on ] > ... zlib: [ on ] > ... lzma: [ on ] > ... get_cpuid: [ OFF ] > ... bpf: [ on ] > ... libaio: [ on ] > ... libzstd: [ on ] > ... disassembler-four-args: [ on ] > > I also could not reproduce on x86: > lsb_release -a: Ubuntu 18.04.1 LTS > gcc --version: gcc (Ubuntu 7.4.0-1ubuntu1~18.04aka10.0.0) 7.4.0 > uname -r: 4.4.0-154-generic I isolated the problem to libcap-dev - if it is not installed a segmentation fault will occur. Since this set is about using capabilities it is obvious that not having it on a system should fail a trace session, but it should not crash it. If libcap-dev is not installed function symbol__restricted_filename() will return true, which in turn will prevent symbol_name to be set in machine__get_running_kernel_start(). That prevents function map__set_kallsyms_ref_reloc_sym() from being called in machine__create_kernel_maps(), resulting in kmap->ref_reloc_sym being NULL in _perf_event__synthesize_kernel_mmap() and a segmentation fault. I am not sure how this can be fixed. I counted a total of 19 instances where kmap->ref_reloc_sym->XYZ is called, only 2 of wich care to check if kmap->ref_reloc_sym is valid before proceeding. As such I must hope that in the 17 other cases, kmap->ref_reloc_sym is guaranteed to be valid. If I am correct then all we need is to check for a valid pointer in _perf_event__synthesize_kernel_mmap(). Otherwise it will be a little harder. Mathieu