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 38F32C433EF for ; Wed, 6 Apr 2022 12:43:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230329AbiDFMp1 (ORCPT ); Wed, 6 Apr 2022 08:45:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55044 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231908AbiDFMoq (ORCPT ); Wed, 6 Apr 2022 08:44:46 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7304F58967D for ; Wed, 6 Apr 2022 01:47:55 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KYJ5F57xNzgYR6; Wed, 6 Apr 2022 16:46:09 +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; Wed, 6 Apr 2022 16:47:53 +0800 Subject: Re: [PATCH] mm/swapfile: unuse_pte can map random data if swap read fails To: Matthew Wilcox , David Hildenbrand CC: , , References: <20220401072926.45051-1-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <23943d63-1fc4-68ce-938f-0f9b53950710@huawei.com> Date: Wed, 6 Apr 2022 16:47:52 +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: dggems703-chm.china.huawei.com (10.3.19.180) 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 2022/4/4 22:11, Matthew Wilcox wrote: > On Mon, Apr 04, 2022 at 03:37:36PM +0200, David Hildenbrand wrote: >> On 01.04.22 09:29, Miaohe Lin wrote: >>> There is a bug in unuse_pte(): when swap page happens to be unreadable, >>> page filled with random data is mapped into user address space. The fix >>> is to check for PageUptodate and fail swapoff in case of error. >>> >>> Signed-off-by: Miaohe Lin >>> --- >>> mm/swapfile.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/mm/swapfile.c b/mm/swapfile.c >>> index 63c61f8b2611..e72a35de7a0f 100644 >>> --- a/mm/swapfile.c >>> +++ b/mm/swapfile.c >>> @@ -1795,6 +1795,10 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, >>> ret = 0; >>> goto out; >>> } >>> + if (unlikely(!PageUptodate(page))) { >>> + ret = -EIO; >>> + goto out; >>> + } >> >> Yeah, we have the same handling in do_swap_page(), whereby we send a >> SIGBUS because we're dealing with an actual access. >> >> Interestingly, folio_test_uptodate() states: >> >> "Anonymous and CoW folios are always uptodate." >> >> @Willy, is that true or is the swapin case not documented there? > > Why do we keep a !Uptodate page in the swap cache? If it can't be > read in from swap, I thought we just freed the page. Since Miaohe We could free the bad page. But we still need a way to prevent user from accessing the wrong data. > has observed that not happening, I guess it doesn't work that way, > but why not make it work that way? How could we make it work that way? Could you please tell me in more detail? Or any suggestions? Many thanks! > > . >