From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B4EA3C43441 for ; Thu, 29 Nov 2018 18:16:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 817CA213A2 for ; Thu, 29 Nov 2018 18:16:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 817CA213A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728132AbeK3FXN (ORCPT ); Fri, 30 Nov 2018 00:23:13 -0500 Received: from foss.arm.com ([217.140.101.70]:42668 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726650AbeK3FXN (ORCPT ); Fri, 30 Nov 2018 00:23:13 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A3E0980D; Thu, 29 Nov 2018 10:16:57 -0800 (PST) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.113]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 88E2A3F575; Thu, 29 Nov 2018 10:16:53 -0800 (PST) Date: Thu, 29 Nov 2018 18:16:51 +0000 From: Catalin Marinas To: Andrey Konovalov Cc: Mark Rutland , Kate Stewart , "open list:DOCUMENTATION" , Will Deacon , Kostya Serebryany , "open list:KERNEL SELFTEST FRAMEWORK" , Chintan Pandya , Shuah Khan , Ingo Molnar , linux-arch , Jacob Bramley , Dmitry Vyukov , Evgeniy Stepanov , Kees Cook , Ruben Ayrapetyan , Ramana Radhakrishnan , Linux ARM , Linux Memory Management List , Greg Kroah-Hartman , LKML , Luc Van Oostenryck , Lee Smith , Andrew Morton , Robin Murphy , "Kirill A . Shutemov" Subject: Re: [PATCH v8 0/8] arm64: untag user pointers passed to the kernel Message-ID: <20181129181650.GG22027@arrakis.emea.arm.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andrey, On Thu, Nov 08, 2018 at 03:48:10PM +0100, Andrey Konovalov wrote: > On Thu, Nov 8, 2018 at 3:36 PM, Andrey Konovalov wrote: > > Changes in v8: > > - Rebased onto 65102238 (4.20-rc1). > > - Added a note to the cover letter on why syscall wrappers/shims that untag > > user pointers won't work. > > - Added a note to the cover letter that this patchset has been merged into > > the Pixel 2 kernel tree. > > - Documentation fixes, in particular added a list of syscalls that don't > > support tagged user pointers. > > I've changed the documentation to be more specific, please take a look. > > I haven't done anything about adding a way for the user to find out > that the kernel supports this ABI extension. I don't know what would > the the preferred way to do this, and we haven't received any comments > on that from anybody else. Probing "on some innocuous syscall > currently returning -EFAULT on tagged pointer arguments" works though, > as you mentioned. We've had some internal discussions and also talked to some people at Plumbers. I think the best option is to introduce an AT_FLAGS bit to describe the ABI relaxation on tagged pointers. Vincenzo is going to propose a patch on top of this series. > As mentioned in the cover letter, this patchset has been merged into > the Pixel 2 kernel tree. I just hope it's not enabled on production kernels, it would introduce a user ABI that may differ from what ends up upstream. -- Catalin