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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=no 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 08B3AC433DB for ; Sat, 20 Mar 2021 16:32:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 64BD361946 for ; Sat, 20 Mar 2021 16:32:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 64BD361946 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 71EFE6B0078; Sat, 20 Mar 2021 12:32:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6BCA06B007B; Sat, 20 Mar 2021 12:32:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 586046B007D; Sat, 20 Mar 2021 12:32:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0219.hostedemail.com [216.40.44.219]) by kanga.kvack.org (Postfix) with ESMTP id 3C5196B0078 for ; Sat, 20 Mar 2021 12:32:42 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id EE0B312CB for ; Sat, 20 Mar 2021 16:32:41 +0000 (UTC) X-FDA: 77940796122.25.1748E89 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf10.hostedemail.com (Postfix) with ESMTP id 76CAE407F8C4 for ; Sat, 20 Mar 2021 16:32:41 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 5060161944; Sat, 20 Mar 2021 16:32:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1616257958; bh=Bl8G1B2SSUB12O7P9gYaeP6Qr+D8nLA7fC0tOMa56nM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=pdm+IlCZPt2t0IVKks5H0qWalupAigJeOR8ZAdo0+W1DtWi1KPYuepKOOZMfYbDEe N+Bbra1Ll95QtzAX7cTnuh58I/o3wtH6zyx9BIOprHyO+SL+XyKEkncKobqfKESA9v ZPjIFy3HrtIG4XT72bU5ZpWjtx6mNAgbcgAVBa1Q= Date: Sat, 20 Mar 2021 09:32:37 -0700 From: Andrew Morton To: Bui Quang Minh Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Peter Xu , Andrea Arcangeli , Axel Rasmussen Subject: Re: [PATCH] userfaultfd: Write protect when virtual memory range has no page table entry Message-Id: <20210320093237.c369eba59a0e5f452109c4ef@linux-foundation.org> In-Reply-To: <20210319152428.52683-1-minhquangbui99@gmail.com> References: <20210319152428.52683-1-minhquangbui99@gmail.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 76CAE407F8C4 X-Stat-Signature: chbgfqsdmy4ugde39b1oqj5b7s5gjusq Received-SPF: none (linux-foundation.org>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616257961-131909 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000106, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 19 Mar 2021 22:24:28 +0700 Bui Quang Minh wrote: > userfaultfd_writeprotect() use change_protection() to clear write bit in > page table entries (pte/pmd). So, later write to this virtual address > range causes a page fault, which is then handled by userspace program. > However, change_protection() has no effect when there is no page table > entries associated with that virtual memory range (a newly mapped memory > range). As a result, later access to that memory range causes allocating a > page table entry with write bit still set (due to VM_WRITE flag in > vma->vm_flags). > > Add checks for VM_UFFD_WP in vma->vm_flags when allocating new page table > entry in missing page table entry page fault path. This sounds like a pretty significant bug? Would it be possible to add a test to tools/testing/selftests/vm/userfaultfd.c to check for this? It should fail without your patch and succeed with it. Thanks.