From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754921AbaCZAYa (ORCPT ); Tue, 25 Mar 2014 20:24:30 -0400 Received: from mga02.intel.com ([134.134.136.20]:56067 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752163AbaCZAY3 (ORCPT ); Tue, 25 Mar 2014 20:24:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,732,1389772800"; d="scan'208";a="480016547" Message-ID: <53321E3B.8080709@linux.intel.com> Date: Tue, 25 Mar 2014 17:24:27 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: David Miller , dborkman@redhat.com CC: ast@plumgrid.com, netdev@vger.kernel.org, hagen@jauu.net, keescook@chromium.org, pmoore@redhat.com, mingo@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next v2 8/9] net: filter: rework/optimize internal BPF interpreter's instruction set References: <1395749457-16178-1-git-send-email-dborkman@redhat.com> <1395749457-16178-9-git-send-email-dborkman@redhat.com> <20140325.201712.1651156258234145348.davem@davemloft.net> In-Reply-To: <20140325.201712.1651156258234145348.davem@davemloft.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/25/2014 05:17 PM, David Miller wrote: > From: Daniel Borkmann > Date: Tue, 25 Mar 2014 13:10:56 +0100 > >> - Conditional jt/jf targets replaced with jt/fall-through, >> and forward/backward jumps now possible as well > > Ummm... does anyone even remember why backwards jumps were not allowed > in the original BPF? > > It's to guarentee forward progress in the filter. > > Allowing branching backward would allow endless loops. > > Please remove this feature. > If you allow loops, it greatly increases the expressibility of the language, but we would really need another control to limit CPU usage. -hpa