From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-he1eur01on0083.outbound.protection.outlook.com ([104.47.0.83]:4398 "EHLO EUR01-HE1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752437AbeF0PIR (ORCPT ); Wed, 27 Jun 2018 11:08:17 -0400 Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel References: <20180626172900.ufclp2pfrhwkxjco@armageddon.cambridge.arm.com> From: Ramana Radhakrishnan Message-ID: <0cef1643-a523-98e7-95e2-9ec595137642@arm.com> Date: Wed, 27 Jun 2018 16:08:09 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andrey Konovalov , Catalin Marinas Cc: Will Deacon , Mark Rutland , Robin Murphy , Al Viro , Kees Cook , Kate Stewart , Greg Kroah-Hartman , Andrew Morton , Ingo Molnar , "Kirill A . Shutemov" , Shuah Khan , Linux ARM , "linux-doc@vger.kernel.org" , Linux Memory Management List , "linux-arch@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , LKML , Chintan Pandya , Jacob Bramley , Ruben Ayrapetyan , Lee Smith , Kostya Serebryany , Dmitry Vyukov , Evgeniy Stepanov nd Message-ID: <20180627150809.UNjROcTjtZkz5gUprdDlcUMxdMZV-n4MxBcm4AG-PFg@z> On 27/06/2018 16:05, Andrey Konovalov wrote: > On Tue, Jun 26, 2018 at 7:29 PM, Catalin Marinas > wrote: >> Hi Andrey, >> >> On Tue, Jun 26, 2018 at 02:47:50PM +0200, Andrey Konovalov wrote: >>> On Wed, Jun 20, 2018 at 5:24 PM, Andrey Konovalov wrote: >>>> arm64 has a feature called Top Byte Ignore, which allows to embed pointer >>>> tags into the top byte of each pointer. Userspace programs (such as >>>> HWASan, a memory debugging tool [1]) might use this feature and pass >>>> tagged user pointers to the kernel through syscalls or other interfaces. >>>> >>>> This patch makes a few of the kernel interfaces accept tagged user >>>> pointers. The kernel is already able to handle user faults with tagged >>>> pointers and has the untagged_addr macro, which this patchset reuses. >>>> >>>> We're not trying to cover all possible ways the kernel accepts user >>>> pointers in one patchset, so this one should be considered as a start. >>>> >>>> Thanks! >>>> >>>> [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html >>> >>> Is there anything I should do to move forward with this? >>> >>> I've received zero replies to this patch set (v3 and v4) over the last >>> month. >> >> The patches in this series look fine but my concern is that they are not >> sufficient and we don't have (yet?) a way to identify where such >> annotations are required. You even say in patch 6 that this is "some >> initial work for supporting non-zero address tags passed to the kernel". >> Unfortunately, merging (or relaxing) an ABI without a clear picture is >> not really feasible. >> >> While I support this work, as a maintainer I'd like to understand >> whether we'd be in a continuous chase of ABI breaks with every kernel >> release or we have a better way to identify potential issues. Is there >> any way to statically analyse conversions from __user ptr to long for >> example? Or, could we get the compiler to do this for us? > > > OK, got it, I'll try to figure out a way to find these conversions. This sounds like the kind of thing we should be able to get sparse to do already, no ? It's been many years since I last looked at it but I thought sparse was the tool of choice in the kernel to do this kind of checking. regards Ramana > > Thanks! >