From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f180.google.com (mail-ig0-f180.google.com [209.85.213.180]) by kanga.kvack.org (Postfix) with ESMTP id AC5B96B0255 for ; Mon, 14 Dec 2015 18:39:32 -0500 (EST) Received: by mail-ig0-f180.google.com with SMTP id ph11so95580135igc.1 for ; Mon, 14 Dec 2015 15:39:32 -0800 (PST) Received: from mail-io0-x236.google.com (mail-io0-x236.google.com. [2607:f8b0:4001:c06::236]) by mx.google.com with ESMTPS id o35si266234ioi.152.2015.12.14.15.39.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 14 Dec 2015 15:39:32 -0800 (PST) Received: by mail-io0-x236.google.com with SMTP id e126so1333063ioa.1 for ; Mon, 14 Dec 2015 15:39:32 -0800 (PST) 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 Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: LKML , Linux-MM , "x86@kernel.org" , Linus Torvalds , Andrew Morton , Andy Lutomirski , Dave Hansen 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org