From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f193.google.com ([209.85.222.193]:44668 "EHLO mail-qk1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727780AbeJRGbk (ORCPT ); Thu, 18 Oct 2018 02:31:40 -0400 Received: by mail-qk1-f193.google.com with SMTP id y8-v6so17587541qka.11 for ; Wed, 17 Oct 2018 15:33:52 -0700 (PDT) Date: Wed, 17 Oct 2018 16:33:47 -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: <20181017223347.GC14047@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: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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. Oh, if we decide to use the padded space? Yes, that makes sense. Ok, I'll switch it to a version. Tycho