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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 BA29AC28CBC for ; Wed, 6 May 2020 19:38:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9699C2075A for ; Wed, 6 May 2020 19:38:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="bJBtLCbp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729279AbgEFTiX (ORCPT ); Wed, 6 May 2020 15:38:23 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:34504 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729316AbgEFTiW (ORCPT ); Wed, 6 May 2020 15:38:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588793901; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=4yGP/vMyHodm9DIXtqpc9Y5085eYUUAufi7jwsRMqFY=; b=bJBtLCbpiYSfHeOTzpKfxlnfTdkiWiffsuNOi8hZY/kUUDYAgDYF4H+1DYaUuUdnO1cYPx g+LFd4QUn8FTapE7XEndlCuW8mPDfovnDjEveKLgzgHm/QJkQbnugEyy2P+HykxUDJ98Li pwG3EDYCKx2GHvMna8U9W8VkfxAEMDc= Received: from mail-qk1-f198.google.com (mail-qk1-f198.google.com [209.85.222.198]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-241-BghV_ulkOQ2QF-S-a2gkMA-1; Wed, 06 May 2020 15:38:19 -0400 X-MC-Unique: BghV_ulkOQ2QF-S-a2gkMA-1 Received: by mail-qk1-f198.google.com with SMTP id h186so2936349qkc.22 for ; Wed, 06 May 2020 12:38:19 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=4yGP/vMyHodm9DIXtqpc9Y5085eYUUAufi7jwsRMqFY=; b=AqKRs8HdLTrqQyJTZjhggDjTDSOzUYG6d2jVs0BIMxD3Ajxuh+4dFpcTLr6LyI9LTN Z1FAJ6xuziyUmLTFpUDjPOyguirK4xryQ8i8VqIJ0/wSNVInH3TRNG08TEHu55mR+8wt NcPpoid+toVroVOlGi59f4L8AKrdLaNAC3gBww2Dn6CDx+wT9XKSfTPSCtsLnRJ6sdNh UhMbwj8yKBukAPswoC/xK/DyqNfoslT2lIRiGFEgcwNzvpTusoCwd0JSgL+hGnKxXn+j jfFJ7epqjrw4Y1rwtod461rQ8mefDgOPay3Ui+mSU1I8FFwUTwXDuBBdoDPWc1NjvuUx KCFw== X-Gm-Message-State: AGi0PuZnno0bcnGDPjp0LkE3MERLEmnVN9YhLxxv4b6TA+fgosqV70k6 GSDs7TVvz5p5i6ia+oXo3F89gRp2oWlD8Cm3+tNjJ45YGFsmpVfp3sZdXTbWeuQNf2SR+87O/Vw B5WqW+YTGMQweRUhiIvfkXIjHVw== X-Received: by 2002:ac8:6cf:: with SMTP id j15mr10289654qth.143.1588793899434; Wed, 06 May 2020 12:38:19 -0700 (PDT) X-Google-Smtp-Source: APiQypJgeGRbgQoROxq+NzNkpj9p1DQBrBYEowm2aG2YpEWn4T7EEcbZzi+caA0aMstz/KZmNOVVMA== X-Received: by 2002:ac8:6cf:: with SMTP id j15mr10289631qth.143.1588793899217; Wed, 06 May 2020 12:38:19 -0700 (PDT) Received: from xz-x1 ([2607:9880:19c0:32::2]) by smtp.gmail.com with ESMTPSA id h188sm2445057qke.82.2020.05.06.12.38.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 May 2020 12:38:18 -0700 (PDT) Date: Wed, 6 May 2020 15:38:16 -0400 From: Peter Xu To: Daniel Colascione Cc: Jonathan Corbet , Alexander Viro , Luis Chamberlain , Kees Cook , Iurii Zaikin , Mauro Carvalho Chehab , Andrew Morton , Andy Shevchenko , Vlastimil Babka , Mel Gorman , Sebastian Andrzej Siewior , Andrea Arcangeli , Mike Rapoport , Jerome Glisse , Shaohua Li , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, timmurray@google.com, minchan@google.com, sspatil@google.com, lokeshgidra@google.com Subject: Re: [PATCH 2/2] Add a new sysctl knob: unprivileged_userfaultfd_user_mode_only Message-ID: <20200506193816.GB228260@xz-x1> References: <20200423002632.224776-1-dancol@google.com> <20200423002632.224776-3-dancol@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200423002632.224776-3-dancol@google.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Apr 22, 2020 at 05:26:32PM -0700, Daniel Colascione wrote: > +unprivileged_userfaultfd_user_mode_only > +======================================== > + > +This flag controls whether unprivileged users can use the userfaultfd > +system calls to handle page faults in kernel mode. If set to zero, > +userfaultfd works with or without UFFD_USER_MODE_ONLY, modulo > +unprivileged_userfaultfd above. If set to one, users without > +SYS_CAP_PTRACE must pass UFFD_USER_MODE_ONLY in order for userfaultfd > +to succeed. Prohibiting use of userfaultfd for handling faults from > +kernel mode may make certain vulnerabilities more difficult > +to exploit. > + > +The default value is 0. If this is going to be added... I am thinking whether it should be easier to add another value for unprivileged_userfaultfd, rather than a new sysctl. E.g.: "0": unprivileged userfaultfd forbidden "1": unprivileged userfaultfd allowed (both user/kernel faults) "2": unprivileged userfaultfd allowed (only user faults) Because after all unprivileged_userfaultfd_user_mode_only will be meaningless (iiuc) if unprivileged_userfaultfd=0. The default value will also be the same as before ("1") then. Thanks, -- Peter Xu