From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932835AbdKAMGB (ORCPT ); Wed, 1 Nov 2017 08:06:01 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:46440 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932356AbdKAMGA (ORCPT ); Wed, 1 Nov 2017 08:06:00 -0400 Date: Wed, 1 Nov 2017 12:05:55 +0000 From: Mark Rutland To: Laura Abbott Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Catalin Marinas , Kees Cook , Will Deacon Subject: Re: [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks Message-ID: <20171101120555.yvb65g3wgtxskfh3@lakrids.cambridge.arm.com> References: <20171026090942.7041-1-mark.rutland@arm.com> <77c80381-cf68-aa1a-9112-e057c068eeb6@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <77c80381-cf68-aa1a-9112-e057c068eeb6@redhat.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 31, 2017 at 04:56:39PM -0700, Laura Abbott wrote: > On 10/26/2017 02:09 AM, Mark Rutland wrote: > > In Prague, Kees mentioned that it would be nice to have a mechanism to > > catch bad __{get,put}_user uses, such as the recent CVE-2017-5123 [1,2] > > issue with unsafe_put_user() in waitid(). > > > > These patches allow an optional access_ok() check to be dropped in > > arm64's __{get,put}_user() primitives. These will then BUG() if a bad > > user pointer is passed (which should only happen in the absence of an > > earlier access_ok() check). > Turning on the option fails as soon as we hit userspace. On my buildroot > based environment I get the help text for ld.so (????) and then a message > about attempting to kill init. Ouch. Thanks for the report, and sorry about this. The problem is that I evaluate the ptr argument twice in __{get,put}_user(), and this may have side effects. e.g. when the ELF loader does things like: __put_user((elf_addr_t)p, sp++) ... we increment sp twice, and write to the wrong user address, leaving sp corrupt. I have an additional patch [1] to fix this, which is in my arm64/access-ok branch [2]. Thanks, Mark. [1] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?h=arm64/access-ok&id=ebb7ff83eb53b8810395d5cf48712a4ae6d678543 [2] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/access-ok