Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933105AbbLNXjg (ORCPT ); Mon, 14 Dec 2015 18:39:36 -0500 Received: from mail-io0-f172.google.com ([209.85.223.172]:35937 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933085AbbLNXjc (ORCPT ); Mon, 14 Dec 2015 18:39:32 -0500 MIME-Version: 1.0 In-Reply-To: <566F52CE.6080501@sr71.net> References: <20151214190542.39C4886D@viggo.jf.intel.com> <20151214190632.6A741188@viggo.jf.intel.com> <566F52CE.6080501@sr71.net> Date: Mon, 14 Dec 2015 15:39:31 -0800 Message-ID: Subject: Re: [PATCH 31/32] x86, pkeys: execute-only support From: Kees Cook To: Dave Hansen Cc: LKML , Linux-MM , "x86@kernel.org" , Linus Torvalds , Andrew Morton , Andy Lutomirski , 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: 1754 Lines: 41 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? Yeah, dunno. I was curious to see this working on a real example first, and then we could figure out how the linker should behave generally. Sounds like we need some kind of ELF flag to say "please use unreadable-exec memory mappings for this program, too. -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/