From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f70.google.com (mail-oi0-f70.google.com [209.85.218.70]) by kanga.kvack.org (Postfix) with ESMTP id 5011D6B0299 for ; Tue, 26 Jun 2018 13:29:09 -0400 (EDT) Received: by mail-oi0-f70.google.com with SMTP id x132-v6so7668114oif.21 for ; Tue, 26 Jun 2018 10:29:09 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id p41-v6si703176oth.68.2018.06.26.10.29.08 for ; Tue, 26 Jun 2018 10:29:08 -0700 (PDT) Date: Tue, 26 Jun 2018 18:29:01 +0100 From: Catalin Marinas Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel Message-ID: <20180626172900.ufclp2pfrhwkxjco@armageddon.cambridge.arm.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Andrey Konovalov 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 , Ramana Radhakrishnan , Evgeniy Stepanov 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? Thanks. -- Catalin