From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f169.google.com (mail-ob0-f169.google.com [209.85.214.169]) by kanga.kvack.org (Postfix) with ESMTP id 306186B0257 for ; Mon, 14 Dec 2015 18:39:49 -0500 (EST) Received: by obc18 with SMTP id 18so144314781obc.2 for ; Mon, 14 Dec 2015 15:39:49 -0800 (PST) Received: from mail-oi0-x22a.google.com (mail-oi0-x22a.google.com. [2607:f8b0:4003:c06::22a]) by mx.google.com with ESMTPS id mp2si5754982oeb.77.2015.12.14.15.39.48 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 14 Dec 2015 15:39:48 -0800 (PST) Received: by oigy66 with SMTP id y66so28721297oig.0 for ; Mon, 14 Dec 2015 15:39:48 -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> From: Andy Lutomirski Date: Mon, 14 Dec 2015 15:39:28 -0800 Message-ID: Subject: Re: [PATCH 31/32] x86, pkeys: execute-only support Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Kees Cook , LKML , Linux-MM , "x86@kernel.org" , Linus Torvalds , Andrew Morton , 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? > Why? Wouldn't --x just end up acting like r-x if PKRU is absent? --Andy -- Andy Lutomirski AMA Capital Management, LLC -- 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