Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933137AbbLNXly (ORCPT ); Mon, 14 Dec 2015 18:41:54 -0500 Received: from mail-io0-f172.google.com ([209.85.223.172]:36522 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932535AbbLNXlx (ORCPT ); Mon, 14 Dec 2015 18:41:53 -0500 MIME-Version: 1.0 In-Reply-To: References: <20151214190542.39C4886D@viggo.jf.intel.com> <20151214190632.6A741188@viggo.jf.intel.com> <566F52CE.6080501@sr71.net> Date: Mon, 14 Dec 2015 15:41:52 -0800 Message-ID: Subject: Re: [PATCH 31/32] x86, pkeys: execute-only support From: Kees Cook To: Andy Lutomirski Cc: Dave Hansen , LKML , Linux-MM , "x86@kernel.org" , Linus Torvalds , Andrew Morton , Dave Hansen Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1971 Lines: 48 On Mon, Dec 14, 2015 at 3:39 PM, Andy Lutomirski wrote: > On Mon, Dec 14, 2015 at 3:37 PM, Dave Hansen wrote: >> On 12/14/2015 12:05 PM, Kees Cook wrote: >>> On Mon, Dec 14, 2015 at 11:06 AM, Dave Hansen wrote: >>>> > From: Dave Hansen >>>> > Protection keys provide new page-based protection in hardware. >>>> > But, they have an interesting attribute: they only affect data >>>> > accesses and never affect instruction fetches. That means that >>>> > if we set up some memory which is set as "access-disabled" via >>>> > protection keys, we can still execute from it. >> ... >>>> > I haven't found any userspace that does this today. >>> To realistically take advantage of this, it sounds like the linker >>> would need to know to keep bss and data page-aligned away from text, >>> and then set text to PROT_EXEC only? >>> >>> Do you have any example linker scripts for this? >> >> Nope. My linker-fu is weak. >> >> Can we even depend on the linker by itself? Even if the sections were >> marked --x, we can't actually use them with those permissions unless we >> have protection keys. >> >> Do we need some special tag on the section to tell the linker to map it >> as --x under some conditions and r-x for others? >> > > Why? Wouldn't --x just end up acting like r-x if PKRU is absent? Good point! What was the mixed section problem that came up before? I realize I said "bss/data" before, but that's not right: those are already page-aligned since they're writable, and rodata would be too, only non-executable. What was the case of memory that needed to be readable? ENEEDCOFFEE. -Kees -- Kees Cook Chrome OS & Brillo Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/