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, URIBL_BLOCKED,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 58C0EECDE32 for ; Wed, 17 Oct 2018 20:29:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 09A51205C9 for ; Wed, 17 Oct 2018 20:29:39 +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="gQF6Cfbx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 09A51205C9 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 S1727883AbeJRE07 (ORCPT ); Thu, 18 Oct 2018 00:26:59 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:40509 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725798AbeJRE07 (ORCPT ); Thu, 18 Oct 2018 00:26:59 -0400 Received: by mail-pl1-f195.google.com with SMTP id 1-v6so13223581plv.7 for ; Wed, 17 Oct 2018 13:29:37 -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=FCQASoYRSaFzlH8fQN2IkGFzJDnxB4c3yZeFtDyQ6uA=; b=gQF6CfbxT7dpq9qMO4/5h2rOPvSTIRIInP2kk+siMkC8QOg5c5kinUWfEPzzOcXAh9 xdoHyqV69ZALqv07+soF0Lzy28MM9rFbCCpf4CJKcNInmgQhfeIWojx2v+3cVPXqAHhf 3GPeuHEioN8QuZJ3Wod2YPINzCOX8gIGuj3c7cU8C77/QQIQedv1xvpTXIKKvFE2sZkW XrXrxvqQa0uGNEDDj1+eltlM9AtXcsIE6p+NgYebPb44ZQU26XeaM3Ys7XJhJFW0rvLy Ptr8dKXLpeflNRonHH/RubGK6FmZKGJ3s3IdUxmhWyM2YCOYFuqOR7CIJWHkxInrlneW dOoA== 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=FCQASoYRSaFzlH8fQN2IkGFzJDnxB4c3yZeFtDyQ6uA=; b=OSpdZMgPB817z1o5qA2aMZvGxMCDX+cXHWvvZRLbYIy6GKLQljS/tnJbEIdwiIiseW ow+Ic0xR4AWOTyVr0ca6CfwkHx7Mw47SD6XbB+7h3sKlWNsMrhYgf30D1R/RdJN/KRYL QzHtqherQOFxZoBe7wXxVHlb3idrt1B6kNSyro7Ob0LCjiA9XNjwATvnpU9CxAdlN+u4 MypaqZbwtQEwN6zKaE5/gZSjJr4Cq0I4pT6pJWdrpMzOlvrabzSIzov7LL7HFfp/NH+k bD24fN4maoZQ1XF6bBNabQIR4OBbszJ7fT531Kz/2a75bm+Xtc/W6208lknXJ0hDVuFh yTlQ== X-Gm-Message-State: ABuFfogvbVr0GyYyWmsYXWo/GmnFWrC+bI8rMeKOil5cXHhM2G3/REG0 KQcpgAUq3UdQ8p0Z/qTvNxIvJg== X-Google-Smtp-Source: ACcGV61fhAxrZa9j28teOHkm2u6RSoGloLQmvEhcVJSuVXAcMVzN+xh3fJZTEzWasc3qMABnlmlQVg== X-Received: by 2002:a17:902:9047:: with SMTP id w7-v6mr27183566plz.4.1539808176278; Wed, 17 Oct 2018 13:29:36 -0700 (PDT) Received: from cisco ([128.107.241.189]) by smtp.gmail.com with ESMTPSA id y7-v6sm20459392pfl.57.2018.10.17.13.29.34 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 17 Oct 2018 13:29:35 -0700 (PDT) Date: Wed, 17 Oct 2018 14:29:33 -0600 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: <20181017202933.GB14047@cisco> References: <20180927151119.9989-1-tycho@tycho.ws> <20180927151119.9989-2-tycho@tycho.ws> 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 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. Tycho