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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 B4CC8C28CF6 for ; Wed, 1 Aug 2018 17:43:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 79378208AC for ; Wed, 1 Aug 2018 17:43:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 79378208AC 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 S2390509AbeHAT3w (ORCPT ); Wed, 1 Aug 2018 15:29:52 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:46000 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389882AbeHAT3v (ORCPT ); Wed, 1 Aug 2018 15:29:51 -0400 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 7BA9480D; Wed, 1 Aug 2018 10:43:03 -0700 (PDT) Received: from armageddon.cambridge.arm.com (armageddon.emea.arm.com [10.4.13.16]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5A79E3F5BA; Wed, 1 Aug 2018 10:42:59 -0700 (PDT) Date: Wed, 1 Aug 2018 18:42:56 +0100 From: Catalin Marinas To: Andrey Konovalov Cc: Mark Rutland , Kate Stewart , linux-doc@vger.kernel.org, Will Deacon , Kostya Serebryany , linux-kselftest@vger.kernel.org, Chintan Pandya , Shuah Khan , Ingo Molnar , linux-arch@vger.kernel.org, Jacob Bramley , Dmitry Vyukov , Evgeniy Stepanov , Kees Cook , Ruben Ayrapetyan , Ramana Radhakrishnan , Al Viro , Linux ARM , Linux Memory Management List , Greg Kroah-Hartman , LKML , Lee Smith , Andrew Morton , Robin Murphy , "Kirill A . Shutemov" Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel Message-ID: <20180801174256.5mbyf33eszml4nmu@armageddon.cambridge.arm.com> References: <20180626172900.ufclp2pfrhwkxjco@armageddon.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 16, 2018 at 01:25:59PM +0200, Andrey Konovalov wrote: > On Thu, Jun 28, 2018 at 9:30 PM, Andrey Konovalov wrote: > > On Wed, Jun 27, 2018 at 5:05 PM, Andrey Konovalov wrote: > >> On Tue, Jun 26, 2018 at 7:29 PM, Catalin Marinas > >> wrote: > >>> 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. > > > > I've prototyped a checker on top of clang static analyzer (initially > > looked at sparse, but couldn't find any documentation or examples). > > The results are here [1], search for "warning: user pointer cast". > > Sharing in case anybody wants to take a look, will look at them myself > > tomorrow. > > > > [1] https://gist.github.com/xairy/433edd5c86456a64026247cb2fef2115 > > So the checker reports ~100 different places where a __user pointer > being casted. I've looked through them and found 3 places where we > need to add untagging. Source code lines below come from 4.18-rc2+ > (6f0d349d). [...] > I'll add the 3 patches with fixes to v5 of this patchset. Thanks for investigating. You can fix those three places in your code but I was rather looking for a way to check such casting in the future for newly added code. While for the khwasan we can assume it's a debug option, the tagged user pointers are ABI and we need to keep it stable. We could we actually add some macros for explicit conversion between __user ptr and long and silence the warning there (I guess this would work better for sparse). We can then detect new ptr to long casts as they appear. I just hope that's not too intrusive. (I haven't tried the sparse patch yet, hopefully sometime this week) -- Catalin