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=-4.7 required=3.0 tests=DATE_IN_PAST_12_24, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable 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 84087C43381 for ; Wed, 20 Mar 2019 06:09:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4F07E2184D for ; Wed, 20 Mar 2019 06:09:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726086AbfCTGJL (ORCPT ); Wed, 20 Mar 2019 02:09:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31937 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725300AbfCTGJL (ORCPT ); Wed, 20 Mar 2019 02:09:11 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DB45883F40; Wed, 20 Mar 2019 06:09:09 +0000 (UTC) Received: from sky.random (ovpn-120-78.rdu2.redhat.com [10.10.120.78]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8C5652E02F; Wed, 20 Mar 2019 06:09:03 +0000 (UTC) Date: Tue, 19 Mar 2019 14:07:29 -0400 From: Andrea Arcangeli To: Mike Rapoport Cc: Peter Xu , linux-kernel@vger.kernel.org, Paolo Bonzini , Hugh Dickins , Luis Chamberlain , Maxime Coquelin , Maya Gokhale , Jerome Glisse , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Denis Plotnikov , linux-mm@kvack.org, Marty McFadden , Mike Kravetz , Mike Rapoport , Kees Cook , Mel Gorman , "Kirill A . Shutemov" , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Dr . David Alan Gilbert" , Andrew Morton Subject: Re: [PATCH v2 1/1] userfaultfd/sysctl: add vm.unprivileged_userfaultfd Message-ID: <20190319180729.GA27618@redhat.com> References: <20190319030722.12441-1-peterx@redhat.com> <20190319030722.12441-2-peterx@redhat.com> <20190319071104.GA6392@rapoport-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190319071104.GA6392@rapoport-lnx> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 20 Mar 2019 06:09:10 +0000 (UTC) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hello, On Tue, Mar 19, 2019 at 09:11:04AM +0200, Mike Rapoport wrote: > Hi Peter, > > On Tue, Mar 19, 2019 at 11:07:22AM +0800, Peter Xu wrote: > > Add a global sysctl knob "vm.unprivileged_userfaultfd" to control > > whether userfaultfd is allowed by unprivileged users. When this is > > set to zero, only privileged users (root user, or users with the > > CAP_SYS_PTRACE capability) will be able to use the userfaultfd > > syscalls. > > > > Suggested-by: Andrea Arcangeli > > Suggested-by: Mike Rapoport > > Signed-off-by: Peter Xu > > Reviewed-by: Mike Rapoport > > Just one minor note below This looks fine with me too. > > + if (!sysctl_unprivileged_userfaultfd && !capable(CAP_SYS_PTRACE)) > > + return -EPERM; The only difference between the bpf sysctl and the userfaultfd sysctl this way is that the bpf sysctl adds the CAP_SYS_ADMIN capability requirement, while userfaultfd adds the CAP_SYS_PTRACE requirement, because the userfaultfd monitor is more likely to need CAP_SYS_PTRACE already if it's doing other kind of tracking on processes runtime, in addition of userfaultfd. In other words both syscalls works only for root, when the two sysctl are opt-in set to 1. Reviewed-by: Andrea Arcangeli