From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f174.google.com (mail-ob0-f174.google.com [209.85.214.174]) by kanga.kvack.org (Postfix) with ESMTP id 3A0D06B0253 for ; Wed, 17 Feb 2016 17:18:06 -0500 (EST) Received: by mail-ob0-f174.google.com with SMTP id xk3so37710623obc.2 for ; Wed, 17 Feb 2016 14:18:06 -0800 (PST) Received: from mail-ob0-x230.google.com (mail-ob0-x230.google.com. [2607:f8b0:4003:c01::230]) by mx.google.com with ESMTPS id u2si4205090oev.32.2016.02.17.14.18.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Feb 2016 14:18:05 -0800 (PST) Received: by mail-ob0-x230.google.com with SMTP id jq7so37444882obb.0 for ; Wed, 17 Feb 2016 14:18:05 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <20160212210152.9CAD15B0@viggo.jf.intel.com> <20160212210240.CB4BB5CA@viggo.jf.intel.com> From: Andy Lutomirski Date: Wed, 17 Feb 2016 14:17:45 -0800 Message-ID: Subject: Re: [PATCH 33/33] x86, pkeys: execute-only support Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Kees Cook Cc: Dave Hansen , X86 ML , Linux-MM , Andrew Morton , LKML , Linus Torvalds , Dave Hansen On Feb 17, 2016 1:27 PM, "Kees Cook" wrote: > > On Fri, Feb 12, 2016 at 1:02 PM, 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. > > > > This patch uses protection keys to set up mappings to do just that. > > If a user calls: > > > > mmap(..., PROT_EXEC); > > or > > mprotect(ptr, sz, PROT_EXEC); > > > > (note PROT_EXEC-only without PROT_READ/WRITE), the kernel will > > notice this, and set a special protection key on the memory. It > > also sets the appropriate bits in the Protection Keys User Rights > > (PKRU) register so that the memory becomes unreadable and > > unwritable. > > > > I haven't found any userspace that does this today. With this > > facility in place, we expect userspace to move to use it > > eventually. Userspace _could_ start doing this today. Any > > PROT_EXEC calls get converted to PROT_READ inside the kernel, and > > would transparently be upgraded to "true" PROT_EXEC with this > > code. IOW, userspace never has to do any PROT_EXEC runtime > > detection. > > Random thought while skimming email: > > Is there a way to detect this feature's availability without userspace > having to set up a segv handler and attempting to read a > PROT_EXEC-only region? (i.e. cpu flag for protection keys, or a way to > check the protection to see if PROT_READ got added automatically, > etc?) > We could add an HWCAP. --Andy -- 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