From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751475AbaLLVlL (ORCPT ); Fri, 12 Dec 2014 16:41:11 -0500 Received: from www.sr71.net ([198.145.64.142]:54234 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750908AbaLLVlK (ORCPT ); Fri, 12 Dec 2014 16:41:10 -0500 Message-ID: <548B60F4.6020903@sr71.net> Date: Fri, 12 Dec 2014 13:41:08 -0800 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Andy Lutomirski CC: "linux-kernel@vger.kernel.org" , Thomas Gleixner , X86 ML Subject: Re: [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels References: <20141212191213.579887D2@viggo.jf.intel.com> <548B4E75.5010507@amacapital.net> <548B4FBE.5090101@sr71.net> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/12/2014 12:48 PM, Andy Lutomirski wrote: > On Fri, Dec 12, 2014 at 12:27 PM, Dave Hansen wrote: >> You want the same size structures with the same format for 32-bit and >> 64-bit modes? > > Yes. Especially because programs can switch between 32-bit and 64-bit > mode entirely in userspace. I don't know whether any do in practice, > but programs *can*. So, you want a 2GB of the 32-bit address space dedicated to a bounds directory, and half of the space for the bounds tables to be simply zero-filled unused address bits? That seems, um, a bit unreasonable. > Or better yet: Intel could have skipped supporting it at all in 32-bit > mode. So, we should not have this security feature for 32-bit apps... because it costs us 50 lines of code in the kernel to support? Did you look at the diffstat? > Isn't mpx somewhat of an address space hog anyway? Yes, it will be troublesome for 32-bit apps that are already bumping up against the virtual address space size to support it. But, really, how many of those *are* there these days?