From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DBD411B87F0; Mon, 10 Mar 2025 06:40:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741588843; cv=none; b=RIloyZiT+9/xreODNnSQSuw+OKsjTHFijh/wMGwyKEV6yplj34LPZ0wHRTKmTI1B299oW9frjg9Zrw12KFthnU1auo8nGGe8LHqlXSVfaDvH8+Ck4yb9bKvjENeUduMXSZiLurO4O+oFjrhQvVdtAf1hL24G6Kcddi1sNNzKgy8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741588843; c=relaxed/simple; bh=CUmqUmoeYlmVdTS9pZtB70jnngGbrZtKj9eGtdxEDsM=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=IZ+1R5xfghXB2+UCwNhOWF90njdayrkp6eQ58SzBCAPC1ylMFT8JyzCvNAh319YVN27QDuj7enOY3e2170Chy9nCfSJTKRWXRIq575FiM8Jn9xJ7AuZ6bBWlY7GqlX+S35snXvmCWsIqRUxyzchqj30bvOuerSOFBKbZP5ngSGg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.17]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4ZB6c1755bz2SSkG; Mon, 10 Mar 2025 14:36:17 +0800 (CST) Received: from kwepemo200002.china.huawei.com (unknown [7.202.195.209]) by mail.maildlp.com (Postfix) with ESMTPS id C31841A0188; Mon, 10 Mar 2025 14:40:36 +0800 (CST) Received: from [10.174.179.13] (10.174.179.13) by kwepemo200002.china.huawei.com (7.202.195.209) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 10 Mar 2025 14:40:35 +0800 Message-ID: Date: Mon, 10 Mar 2025 14:40:35 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: Using userfaultfd with KVM's async page fault handling causes processes to hung waiting for mmap_lock to be released To: Peter Xu , jimsiak CC: , , , , References: <79375b71-db2e-3e66-346b-254c90d915e2@cslab.ece.ntua.gr> <20250307072133.3522652-1-tujinjiang@huawei.com> <46ac83f7-d3e0-b667-7352-d853938c9fc9@huawei.com> From: Jinjiang Tu In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemo200002.china.huawei.com (7.202.195.209) 在 2025/3/8 6:41, Peter Xu 写道: > On Fri, Mar 07, 2025 at 03:11:09PM +0200, jimsiak wrote: >> Hi, >> >> From my side, I managed to avoid the freezing of processes with the >> following change in function userfaultfd_release() in file fs/userfaultfd.c >> (https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L842): >> >> I moved the following command from line 851: >> WRITE_ONCE(ctx->released, true); >> (https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L851) >> >> to line 905, that is exactly before the functions returns 0. >> >> That simple workaround worked for my use case but I am far from sure that is >> a correct/sufficient fix for the problem at hand. > Updating the field after userfaultfd_ctx_put() might mean UAF, afaict. > > Maybe it's possible to remove ctx->released but only rely on the mmap write > lock. However that'll need some closer look and more thoughts. > > To me, the more straightforward way to fix it is to use the patch I > mentioned in the other email: > > https://lore.kernel.org/all/ZLmT3BfcmltfFvbq@x1n/ > > Or does it mean it didn't work at all? This patch works for me. mlock() syscall calls GUP with FOLL_UNLOCKABLE and allows to release mmap lock and retry. But other GUP call without FOLL_UNLOCKABLE will return VM_FAULT_SIGBUS, is it a regression for the below commit？ commit 656710a60e3693911bee3a355d2f2bbae3faba33 Author: Andrea Arcangeli Date: Fri Sep 8 16:12:42 2017 -0700 userfaultfd: non-cooperative: closing the uffd without triggering SIGBUS > > Thanks, >