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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 41AADC43441 for ; Tue, 27 Nov 2018 19:13:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DC0E20663 for ; Tue, 27 Nov 2018 19:13:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0DC0E20663 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727558AbeK1GMA (ORCPT ); Wed, 28 Nov 2018 01:12:00 -0500 Received: from mga14.intel.com ([192.55.52.115]:30885 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727462AbeK1GMA (ORCPT ); Wed, 28 Nov 2018 01:12:00 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Nov 2018 11:13:07 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,287,1539673200"; d="scan'208";a="253430624" Received: from linux.intel.com ([10.54.29.200]) by orsmga004.jf.intel.com with ESMTP; 27 Nov 2018 11:13:07 -0800 Received: from [10.251.85.27] (abudanko-mobl.ccr.corp.intel.com [10.251.85.27]) by linux.intel.com (Postfix) with ESMTP id E953C580322; Tue, 27 Nov 2018 11:13:02 -0800 (PST) Subject: Re: [PATCH v4 1/2] Documentation/admin-guide: introduce perf-security.rst file To: Jonathan Corbet Cc: Thomas Gleixner , Kees Cook , Jann Horn , Ingo Molnar , Peter Zijlstra , Andi Kleen , Alexander Shishkin , Jiri Olsa , Arnaldo Carvalho de Melo , Mark Rutland , Tvrtko Ursulin , linux-kernel , "kernel-hardening@lists.openwall.com" , "linux-doc@vger.kernel.org" References: <20181127111148.75746f02@lwn.net> From: Alexey Budankov Organization: Intel Corp. Message-ID: <5e1e9c08-dff5-956d-4c2b-8ee090c387c3@linux.intel.com> Date: Tue, 27 Nov 2018 22:13:01 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181127111148.75746f02@lwn.net> 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 27.11.2018 21:11, Jonathan Corbet wrote: > On Tue, 27 Nov 2018 11:15:37 +0300 > Alexey Budankov wrote: > >> +To perform security checks, the Linux implementation splits processes into two >> +categories [6]_ : a) privileged processes (whose effective user ID is 0, referred >> +to as superuser or root), and b) unprivileged processes (whose effective UID is >> +nonzero). Privileged processes bypass all kernel security permission checks so >> +perf_events performance monitoring is fully available to privileged processes >> +without access, scope and resource restrictions. >> + >> +Unprivileged processes are subject to a full security permission check based on >> +the process's credentials [5]_ (usually: effective UID, effective GID, and >> +supplementary group list). >> + >> +Linux divides the privileges traditionally associated with superuser into >> +distinct units, known as capabilities [6]_ , which can be independently enabled >> +and disabled on per-thread basis for processes and files of unprivileged users. >> + >> +Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated as >> +privileged processes with respect to perf_events performance monitoring and >> +bypass *scope* permissions checks in the kernel. >> + >> +Unprivileged processes using perf_events system call API is also subject for >> +PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose outcome >> +determines whether monitoring is permitted. So unprivileged processes provided >> +with CAP_SYS_PTRACE capability are effectively permitted to pass the check. > > It's good to have more information here. I could certainly quibble > further with things - a process with CAP_SYS_ADMIN is not "unprivileged"! > - but I don't want to stand in the way of this any further. I *would* > still like to see an ack from the perf world, though. Thanks for meaningful comments! Looking forward to ack from perf world. > > With regard to Kees's comment on merging the two patches; I would probably > add the new document to index.rst in the same patch, but it doesn't matter > that much. Not worth redoing the patch just for that. Thanks, Alexey > > jon >