From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752721AbeC3C1P (ORCPT ); Thu, 29 Mar 2018 22:27:15 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:43746 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751893AbeC3C1N (ORCPT ); Thu, 29 Mar 2018 22:27:13 -0400 Subject: Re: [PATCH net] vhost: validate log when IOTLB is enabled To: "Michael S. Tsirkin" Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <1522310404-8486-1-git-send-email-jasowang@redhat.com> <20180329173438-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Fri, 30 Mar 2018 10:27:07 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180329173438-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018年03月29日 22:44, Michael S. Tsirkin wrote: > On Thu, Mar 29, 2018 at 04:00:04PM +0800, Jason Wang wrote: >> Vq log_base is the userspace address of bitmap which has nothing to do >> with IOTLB. So it needs to be validated unconditionally otherwise we >> may try use 0 as log_base which may lead to pin pages that will lead >> unexpected result (e.g trigger BUG_ON() in set_bit_to_user()). >> >> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API") >> Reported-by:syzbot+6304bf97ef436580fede@syzkaller.appspotmail.com >> Signed-off-by: Jason Wang > One follow-up question: > > We still observe that get user pages returns 0 sometimes. While I agree > we should not pass in unvalidated addresses, isn't this worth > documenting? > > Looking at get_user_pages_fast(), it has:     if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,                     (void __user *)start, len)))         return 0; So this is expected I think. Thanks