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=-10.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 21684C07E96 for ; Thu, 8 Jul 2021 12:58:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0122C61456 for ; Thu, 8 Jul 2021 12:58:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231804AbhGHNB3 (ORCPT ); Thu, 8 Jul 2021 09:01:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:54208 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231755AbhGHNB2 (ORCPT ); Thu, 8 Jul 2021 09:01:28 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id D433D61585; Thu, 8 Jul 2021 12:58:44 +0000 (UTC) Date: Thu, 8 Jul 2021 13:58:42 +0100 From: Catalin Marinas To: Peter Collingbourne Cc: Vincenzo Frascino , Dave Martin , Will Deacon , Andrew Morton , Andrea Arcangeli , Alistair Delva , Lokesh Gidra , William McVicker , Evgenii Stepanov , Mitch Phillips , Linux ARM , linux-mm@kvack.org, Andrey Konovalov , stable@vger.kernel.org Subject: Re: [PATCH v4 1/2] userfaultfd: do not untag user pointers Message-ID: <20210708125841.GA9966@arm.com> References: <20210707184313.3697385-1-pcc@google.com> <20210707184313.3697385-2-pcc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210707184313.3697385-2-pcc@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Jul 07, 2021 at 11:43:12AM -0700, Peter Collingbourne wrote: > If a user program uses userfaultfd on ranges of heap memory, it may > end up passing a tagged pointer to the kernel in the range.start > field of the UFFDIO_REGISTER ioctl. This can happen when using an > MTE-capable allocator, or on Android if using the Tagged Pointers > feature for MTE readiness [1]. > > When a fault subsequently occurs, the tag is stripped from the fault > address returned to the application in the fault.address field > of struct uffd_msg. However, from the application's perspective, > the tagged address *is* the memory address, so if the application > is unaware of memory tags, it may get confused by receiving an > address that is, from its point of view, outside of the bounds of the > allocation. We observed this behavior in the kselftest for userfaultfd > [2] but other applications could have the same problem. > > Address this by not untagging pointers passed to the userfaultfd > ioctls. Instead, let the system call fail. This will provide an > early indication of problems with tag-unaware userspace code instead > of letting the code get confused later, and is consistent with how > we decided to handle brk/mmap/mremap in commit dcde237319e6 ("mm: > Avoid creating virtual address aliases in brk()/mmap()/mremap()"), > as well as being consistent with the existing tagged address ABI > documentation relating to how ioctl arguments are handled. > > The code change is a revert of commit 7d0325749a6c ("userfaultfd: > untag user pointers") plus some fixups to some additional calls to > validate_range that have appeared since then. > > [1] https://source.android.com/devices/tech/debug/tagged-pointers > [2] tools/testing/selftests/vm/userfaultfd.c > > Signed-off-by: Peter Collingbourne > Reviewed-by: Andrey Konovalov > Link: https://linux-review.googlesource.com/id/I761aa9f0344454c482b83fcfcce547db0a25501b > Fixes: 63f0c6037965 ("arm64: Introduce prctl() options to control the tagged user addresses ABI") > Cc: # 5.4 Reviewed-by: Catalin Marinas