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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 9A4BFC2BA12 for ; Fri, 3 Apr 2020 13:56:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 77EF52073B for ; Fri, 3 Apr 2020 13:56:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391009AbgDCN4u (ORCPT ); Fri, 3 Apr 2020 09:56:50 -0400 Received: from mga12.intel.com ([192.55.52.136]:54582 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390883AbgDCN4t (ORCPT ); Fri, 3 Apr 2020 09:56:49 -0400 IronPort-SDR: flEouXuH0PyoTBVneQUKeYeAB/YyK0Qos4o5kKZMbEd3486T4z0trc59S5Y9avwane7faXPgep pffrscfTyYyA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Apr 2020 06:56:48 -0700 IronPort-SDR: sg/BjNhR9EPaUobM7/48I3JxZw/KmrC8Aq4/WNwtGT1eUOuEuvoYSJ4igirXB08rZO+HN27WLt P0imZBIZJ91w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,339,1580803200"; d="scan'208";a="253373358" Received: from linux.intel.com ([10.54.29.200]) by orsmga006.jf.intel.com with ESMTP; 03 Apr 2020 06:56:48 -0700 Received: from [10.249.254.224] (abudanko-mobl.ccr.corp.intel.com [10.249.254.224]) by linux.intel.com (Postfix) with ESMTP id 8DE9E5802C8; Fri, 3 Apr 2020 06:56:45 -0700 (PDT) Subject: Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON privileged process From: Alexey Budankov To: Alexei Starovoitov Cc: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , James Morris , Jiri Olsa , Andi Kleen , Alexander Shishkin , Namhyung Kim , linux-kernel References: <20200108160713.GI2844@hirez.programming.kicks-ass.net> <20200110140234.GO2844@hirez.programming.kicks-ass.net> <20200111005213.6dfd98fb36ace098004bde0e@kernel.org> <20200110164531.GA2598@kernel.org> <20200111084735.0ff01c758bfbfd0ae2e1f24e@kernel.org> <2B79131A-3F76-47F5-AAB4-08BCA820473F@fb.com> <5e191833.1c69fb81.8bc25.a88c@mx.google.com> <158a4033-f8d6-8af7-77b0-20e62ec913b0@linux.intel.com> <20200114122506.3cf442dc189a649d4736f86e@kernel.org> <81abaa29-d1be-a888-8b2f-fdf9b7e9fde8@linux.intel.com> <257a949a-b7cc-5ff1-6f1a-34bc44b1efc5@linux.intel.com> <687dc836-4d86-c281-75b3-c4df451e7cd1@linux.intel.com> Organization: Intel Corp. Message-ID: <6dfd7ded-3294-6ec5-dcc0-92303a5cecb5@linux.intel.com> Date: Fri, 3 Apr 2020 16:56:44 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <687dc836-4d86-c281-75b3-c4df451e7cd1@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01.04.2020 23:50, Alexey Budankov wrote: > Hi Alexei, > > On 15.01.2020 4:52, Alexei Starovoitov wrote: >> On Tue, Jan 14, 2020 at 10:50 AM Alexey Budankov >> wrote: >>> >>> >>> On 14.01.2020 21:06, Alexei Starovoitov wrote: >>>> On Tue, Jan 14, 2020 at 1:47 AM Alexey Budankov >>>> wrote: >>>>>>> >>>>>>> As we talked at RFC series of CAP_SYS_TRACING last year, I just expected >>>>>>> to open it for enabling/disabling kprobes, not for creation. >>>>>>> >>>>>>> If we can accept user who has no admin priviledge but the CAP_SYS_PERFMON, >>>>>>> to shoot their foot by their own risk, I'm OK to allow it. (Even though, >>>>>>> it should check the max number of probes to be created by something like >>>>>>> ulimit) >>>>>>> I think nowadays we have fixed all such kernel crash problems on x86, >>>>>>> but not sure for other archs, especially on the devices I can not reach. >>>>>>> I need more help to stabilize it. >>>>>> >>>>>> I don't see how enable/disable is any safer than creation. >>>>>> If there are kernel bugs in kprobes the kernel will crash anyway. >>>>>> I think such partial CAP_SYS_PERFMON would be very confusing to the users. >>>>>> CAP_* is about delegation of root privileges to non-root. >>>>>> Delegating some of it is ok, but disallowing creation makes it useless >>>>>> for bpf tracing, so we would need to add another CAP later. >>>>>> Hence I suggest to do it right away instead of breaking >>>>>> sys_perf_even_open() access into two CAPs. >>>>>> >>>>> >>>>> Alexei, Masami, >>>>> >>>>> Thanks for your meaningful input. >>>>> If we know in advance that it still can crash the system in some cases and on >>>>> some archs, even though root fully controls delegation thru CAP_SYS_PERFMON, >>>>> such delegation looks premature until the crashes are avoided. So it looks like >>>>> access to eBPF for CAP_SYS_PERFMON privileged processes is the subject for >>>>> a separate patch set. >>>> >>>> perf_event_open is always dangerous. sw cannot guarantee non-bugginess of hw. >>> >>> Sure, software cannot guarantee, but known software bugs could still be fixed, >>> that's what I meant. >>> >>>> imo adding a cap just for pmc is pointless. >>>> if you add a new cap it should cover all of sys_perf_event_open syscall. >>>> subdividing it into sw vs hw counters, kprobe create vs enable, etc will >>>> be the source of ongoing confusion. nack to such cap. >>>> >>> >>> Well, as this patch set already covers complete perf_event_open functionality, >>> and also eBPF related parts too, could you please review and comment on it? >>> Does the patches 2/9 and 5/9 already bring all required extentions? >> >> yes. the current patches 2 and 5 look good to me. > > Could this have you explicit Reviewed-by or Acked-by tag so > the changes could be driven into the kernel? > Latest v7 is here: https://lore.kernel.org/lkml/c8de937a-0b3a-7147-f5ef-69f467e87a13@linux.intel.com/ Posted v8 with all acquired tags so far: https://lore.kernel.org/lkml/f96f8f8a-e65c-3f36-dc85-fc3f5191e8c5@linux.intel.com/ Thanks, Alexey