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=-2.3 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 9150FECDE43 for ; Sun, 21 Oct 2018 16:04:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 365052083C for ; Sun, 21 Oct 2018 16:04:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=tycho-ws.20150623.gappssmtp.com header.i=@tycho-ws.20150623.gappssmtp.com header.b="Tz6+2vzl" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 365052083C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=tycho.ws 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 S1727939AbeJVAT2 (ORCPT ); Sun, 21 Oct 2018 20:19:28 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:42767 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727408AbeJVAT2 (ORCPT ); Sun, 21 Oct 2018 20:19:28 -0400 Received: by mail-wr1-f66.google.com with SMTP id f8-v6so2753190wro.9 for ; Sun, 21 Oct 2018 09:04:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tycho-ws.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=21P02KsXQVVmg3Huv2uEG5HLR0+58fRmI+DDclHAhIw=; b=Tz6+2vzlhYatUQZLbtl9qPc2F9pv1R1bSMqmJ2f/fFFt5lEl5oj0wqcFkgTVnhF/XA zDAHUshEQu8jNuOCNCgwPG/JT01wbqZ6FDbPtjCjOTThNaSqLAP0Q/nPaltvjeRsZXm3 yDYzqbCzcsajzf6u03vCqgCRVuC7P5IE7/thyKxxsgirTIHPVtQBeH4ebSWNOxq376Pf 1SZi+DW+ZOva+A51eAvp+f2gpYhHQeCz10Yl2S3oK0L2QDcnq+cnMucYP6mWQHtyx3R9 9NhwYd+KCtMM0TUGRfCou8j6ZctZ7H4CaqDdcyvrUmeiDCU+4DWWGBwYnCWbiyQqCmqY +ZoA== 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:user-agent; bh=21P02KsXQVVmg3Huv2uEG5HLR0+58fRmI+DDclHAhIw=; b=f4suKSnqwEBkpHV7utYXz6AIc+6YmBvNqLjCsivZJ9y80jLb5/USrFR61DWVYY1UrR VHX3lQJGL67d+wEnHYtUzFApT4A+Mct2XG19SUah4oX3mVvecedpH0VleyhWmTS3NO7Q 2po7r0fShmd+c3mzL8hKYFrjjmv3TeAqpPz58AkAMo+4j9YK622RGwt1h7qaCRq0KEls B5yND0rd9KM6MUQJ522pJkfmRaLCqIepcf615KAwqaBcQSQLWrMW5JFxea5UVGRQD088 n+eXBJ2jIKQ/dtlZJk+JnR2c/ZJcZP/XiaU+8iRfDWVbFt0v2sl3dFWsQA2YXAdF3anv tL3A== X-Gm-Message-State: ABuFfohaxY86s4ae9Iop1/HqJHtREeXmIkGfYljyucLhY0aUi1Ujs76g r8pywA/GJ4uQeqDAL0MBq9KKf2gsk8hF70mm X-Google-Smtp-Source: ACcGV63koRRAhAN79IJols9FxYMh9bYBaUq9je/tRhcenH1LHF4PpAlYPq4wBej3VEOAghvQk8I/pw== X-Received: by 2002:adf:b313:: with SMTP id j19-v6mr21495679wrd.207.1540137879902; Sun, 21 Oct 2018 09:04:39 -0700 (PDT) Received: from cisco ([109.144.219.53]) by smtp.gmail.com with ESMTPSA id l10-v6sm673406wrv.29.2018.10.21.09.04.38 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 21 Oct 2018 09:04:38 -0700 (PDT) Date: Sun, 21 Oct 2018 17:04:37 +0100 From: Tycho Andersen To: Kees Cook Cc: LKML , Linux Containers , Linux API , Andy Lutomirski , Oleg Nesterov , "Eric W . Biederman" , "Serge E . Hallyn" , Christian Brauner , Tyler Hicks , Akihiro Suda , Jann Horn , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH v7 1/6] seccomp: add a return code to trap to userspace Message-ID: <20181021160437.GB25202@cisco> References: <20180927151119.9989-1-tycho@tycho.ws> <20180927151119.9989-2-tycho@tycho.ws> <20181017202933.GB14047@cisco> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 17, 2018 at 03:21:02PM -0700, Kees Cook wrote: > On Wed, Oct 17, 2018 at 1:29 PM, Tycho Andersen wrote: > > On Thu, Sep 27, 2018 at 02:31:24PM -0700, Kees Cook wrote: > >> On Thu, Sep 27, 2018 at 8:11 AM, Tycho Andersen wrote: > >> > @@ -60,4 +62,29 @@ struct seccomp_data { > >> > __u64 args[6]; > >> > }; > >> > > >> > +struct seccomp_notif { > >> > + __u16 len; > >> > + __u64 id; > >> > + __u32 pid; > >> > + __u8 signaled; > >> > + struct seccomp_data data; > >> > +}; > >> > + > >> > +struct seccomp_notif_resp { > >> > + __u16 len; > >> > + __u64 id; > >> > + __s32 error; > >> > + __s64 val; > >> > +}; > >> > >> So, len has to come first, for versioning. However, since it's ahead > >> of a u64, this leaves a struct padding hole. pahole output: > >> > >> struct seccomp_notif { > >> __u16 len; /* 0 2 */ > >> > >> /* XXX 6 bytes hole, try to pack */ > >> > >> __u64 id; /* 8 8 */ > >> __u32 pid; /* 16 4 */ > >> __u8 signaled; /* 20 1 */ > >> > >> /* XXX 3 bytes hole, try to pack */ > >> > >> struct seccomp_data data; /* 24 64 */ > >> /* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */ > >> > >> /* size: 88, cachelines: 2, members: 5 */ > >> /* sum members: 79, holes: 2, sum holes: 9 */ > >> /* last cacheline: 24 bytes */ > >> }; > >> struct seccomp_notif_resp { > >> __u16 len; /* 0 2 */ > >> > >> /* XXX 6 bytes hole, try to pack */ > >> > >> __u64 id; /* 8 8 */ > >> __s32 error; /* 16 4 */ > >> > >> /* XXX 4 bytes hole, try to pack */ > >> > >> __s64 val; /* 24 8 */ > >> > >> /* size: 32, cachelines: 1, members: 4 */ > >> /* sum members: 22, holes: 2, sum holes: 10 */ > >> /* last cacheline: 32 bytes */ > >> }; > >> > >> How about making len u32, and moving pid and error above "id"? This > >> leaves a hole after signaled, so changing "len" won't be sufficient > >> for versioning here. Perhaps move it after data? > > > > Just to confirm my understanding; I've got these as: > > > > struct seccomp_notif { > > __u32 len; /* 0 4 */ > > __u32 pid; /* 4 4 */ > > __u64 id; /* 8 8 */ > > __u8 signaled; /* 16 1 */ > > > > /* XXX 7 bytes hole, try to pack */ > > > > struct seccomp_data data; /* 24 64 */ > > /* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */ > > > > /* size: 88, cachelines: 2, members: 5 */ > > /* sum members: 81, holes: 1, sum holes: 7 */ > > /* last cacheline: 24 bytes */ > > }; > > struct seccomp_notif_resp { > > __u32 len; /* 0 4 */ > > __s32 error; /* 4 4 */ > > __u64 id; /* 8 8 */ > > __s64 val; /* 16 8 */ > > > > /* size: 24, cachelines: 1, members: 4 */ > > /* last cacheline: 24 bytes */ > > }; > > > > in the next version. Since the structure has no padding at the end of > > it, I think the Right Thing will happen. Note that this is slightly > > different than what Kees suggested, if I add signaled after data, then > > I end up with: > > > > struct seccomp_notif { > > __u32 len; /* 0 4 */ > > __u32 pid; /* 4 4 */ > > __u64 id; /* 8 8 */ > > struct seccomp_data data; /* 16 64 */ > > /* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */ > > __u8 signaled; /* 80 1 */ > > > > /* size: 88, cachelines: 2, members: 5 */ > > /* padding: 7 */ > > /* last cacheline: 24 bytes */ > > }; > > > > which I think will have the versioning problem if the next member > > introduces is < 7 bytes. > > It'll be a problem in either place. What I was thinking was that > specific versioning is required instead of just length. Euh, so I implemented this, and it sucks :). It's ugly, and generally feels bad. What if instead we just get rid of versioning all together, and instead introduce a u32 flags? We could have one flag right now (SECCOMP_NOTIF_FLAG_SIGNALED), and use introduce others as we add more information to the response. Then we can add SECCOMP_NOTIF_FLAG_EXTRA_FOO, and add another SECCOMP_IOCTL_GET_FOO to grab the info? FWIW, it's not really clear to me that we'll ever add anything to the response since hopefully we'll land PUT_FD, so maybe this is all moot anyway. Tycho