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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C0330C43334 for ; Tue, 26 Jul 2022 07:14:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E4E3C8E0002; Tue, 26 Jul 2022 03:14:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DFD5D8E0001; Tue, 26 Jul 2022 03:14:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CC4AA8E0002; Tue, 26 Jul 2022 03:14:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id B8EB88E0001 for ; Tue, 26 Jul 2022 03:14:22 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 9299D140562 for ; Tue, 26 Jul 2022 07:14:22 +0000 (UTC) X-FDA: 79728387564.26.8731109 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by imf31.hostedemail.com (Postfix) with ESMTP id 6BB062009D for ; Tue, 26 Jul 2022 07:14:21 +0000 (UTC) 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 ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf31.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.255 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658819662; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sq1rT2+ohKihPdHnoHej9LSI+QTM7e/G4wn0iJki3TA=; b=RQkZSzZSY9uC58hWHHCJ4gVnfHe7uuFYLZoJWleNsHrptubygYFYV8e/PNpO/mtQVBQojU r6Oq6z2PanFGznWrnFh9I29rIFcGllriKDwn6CqYC4DooL459KAj3cx2otsZjD1lt390B+ CIIbIAYtmsQVuYAj59J5i5tS6s6EONc= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658819662; a=rsa-sha256; cv=none; b=x/jGPU8Vh+ZvB4xavN+vA1CAeXyKpBUB+dR4JOWyd9FlbSzTUcP/vrMHLYcaOz1PorDbJ0 Tz2QzFm3GoPjzr+O8EAMsGdPWp9QS2/L3ZCccldtc+MnWGP4fsb9wH75oFSzTY8UUb0TKq bUQLZXNj5KVfWpwFtz7ObyaAS+pJIoQ= X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 6BB062009D X-Rspam-User: Authentication-Results: imf31.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf31.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.255 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Stat-Signature: 3idw5jk7ej7rnnge1trkmtx9apnuqyfs X-HE-Tag: 1658819661-665386 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. :)