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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC06DCCA489 for ; Tue, 26 Jul 2022 07:14:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237854AbiGZHOW (ORCPT ); Tue, 26 Jul 2022 03:14:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49762 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230331AbiGZHOV (ORCPT ); Tue, 26 Jul 2022 03:14:21 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D724F2A969 for ; Tue, 26 Jul 2022 00:14:19 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4LsSkk2dXNz1M8K5; Tue, 26 Jul 2022 15:11:26 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 26 Jul 2022 15:14:17 +0800 Subject: Re: [bug report] mm/hugetlb: possible data leak with huge pmd sharing To: Mike Kravetz CC: Linux-MM , linux-kernel , Andrew Morton , Muchun Song References: <025b3ea6-4b26-f091-5464-0eef5aac7719@huawei.com> From: Miaohe Lin Message-ID: <2ec4cd05-5b3a-cd5c-7785-5a7236804bef@huawei.com> Date: Tue, 26 Jul 2022 15:14:17 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/7/26 2:35, Mike Kravetz wrote: > On 07/25/22 17:07, Miaohe Lin wrote: >> Hi all: >> When I investigate the mm/hugetlb code, I found there's a possible data leak issue >> with huge pmd sharing. Thank about the below scene: >> >> 1. Process A and process B shares huge pmd page.(vm_flags: VM_MAYSHARE but !VM_SHARED) > > Thanks, > > I often get confused about the setting of VM_MAYSHARE and VM_SHARED. When > you throw in the possibility of shared and anonymous, then I struggle a bit > more. At one time did an audit to get the meaning clear in my mind, but still > struggle with the meanings. > > Is it possible to have VM_MAYSHARE and !VM_SHARED on a hugetlb vma? I only > took a quick look and could not find a way for this to happen. But, I> could have easily missed something. Thanks for your reply. It's possible to have VM_MAYSHARE and !VM_SHARED on a hugetlb vma with below code snippet: ... fd = open("/root/huge/hugepagefile", O_CREAT | O_RDONLY, 0755); if (fd < 0) { perror("Open failed"); exit(1); } addr = mmap(0, 32UL*1024*1024, PROT_READ, MAP_SHARED, fd, 0); ... cat /proc//smaps: 400000000000-400002000000 r--s 00000000 00:2f 153780886 /root/huge/hugepagefile Size: 32768 kB KernelPageSize: 2048 kB MMUPageSize: 2048 kB ... VmFlags: rd mr me ms de ht /* sh: VM_SHARED, mw: VM_MAYWRITE, ms:VM_MAYSHARE */ So vm_flags is VM_MAYSHARE but !VM_SHARED. But in this case, it's readonly. So the above scene won't happen. Sorry for make noise. > Thanks for your comment again. :)