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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B23B1C65C20 for ; Mon, 8 Oct 2018 18:47:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76DCB21479 for ; Mon, 8 Oct 2018 18:47:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 76DCB21479 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731493AbeJICAq (ORCPT ); Mon, 8 Oct 2018 22:00:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39030 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730798AbeJICAq (ORCPT ); Mon, 8 Oct 2018 22:00:46 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C5932C034DF4; Mon, 8 Oct 2018 18:47:39 +0000 (UTC) Received: from w520.home (ovpn-116-90.phx2.redhat.com [10.3.116.90]) by smtp.corp.redhat.com (Postfix) with ESMTP id 353575D784; Mon, 8 Oct 2018 18:47:38 +0000 (UTC) Date: Mon, 8 Oct 2018 12:47:38 -0600 From: Alex Williamson To: Wenwen Wang Cc: Kangjie Lu , kvm@vger.kernel.org (open list:VFIO DRIVER), linux-kernel@vger.kernel.org (open list), Subject: Re: [PATCH v2] drivers/vfio: Fix a redundant copy bug Message-ID: <20181008124738.23a547d0@w520.home> In-Reply-To: <1539021980-2412-1-git-send-email-wang6495@umn.edu> References: <1539021980-2412-1-git-send-email-wang6495@umn.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 08 Oct 2018 18:47:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 8 Oct 2018 13:06:20 -0500 Wenwen Wang wrote: > In vfio_spapr_iommu_eeh_ioctl(), if the ioctl command is VFIO_EEH_PE_OP, > the user-space buffer 'arg' is copied to the kernel object 'op' and the > 'argsz' and 'flags' fields of 'op' are checked. If the check fails, an > error code EINVAL is returned. Otherwise, 'op.op' is further checked > through a switch statement to invoke related handlers. If 'op.op' is > VFIO_EEH_PE_INJECT_ERR, the whole user-space buffer 'arg' is copied again > to 'op' to obtain the err information. However, in the following execution > of this case, the fields of 'op', except the field 'err', are actually not > used. That is, the second copy has a redundant part. Therefore, for both > performance consideration, the redundant part of the second copy should be > removed. > > This patch removes such a part in the second copy. It only copies from > 'err.type' to 'err.mask', which is exactly required by the > VFIO_EEH_PE_INJECT_ERR op. > > Signed-off-by: Wenwen Wang > --- > drivers/vfio/vfio_spapr_eeh.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/drivers/vfio/vfio_spapr_eeh.c b/drivers/vfio/vfio_spapr_eeh.c > index 38edeb4..66634c6 100644 > --- a/drivers/vfio/vfio_spapr_eeh.c > +++ b/drivers/vfio/vfio_spapr_eeh.c > @@ -37,6 +37,7 @@ long vfio_spapr_iommu_eeh_ioctl(struct iommu_group *group, > struct eeh_pe *pe; > struct vfio_eeh_pe_op op; > unsigned long minsz; > + unsigned long start, end; > long ret = -EINVAL; > > switch (cmd) { > @@ -86,10 +87,12 @@ long vfio_spapr_iommu_eeh_ioctl(struct iommu_group *group, > ret = eeh_pe_configure(pe); > break; > case VFIO_EEH_PE_INJECT_ERR: > - minsz = offsetofend(struct vfio_eeh_pe_op, err.mask); > - if (op.argsz < minsz) > + start = offsetof(struct vfio_eeh_pe_op, err.type); We already have this in minsz, offsetofend(,op) == offsetof(,err.type). That can't change without breaking userspace. > + end = offsetofend(struct vfio_eeh_pe_op, err.mask); > + if (op.argsz < end) > return -EINVAL; > - if (copy_from_user(&op, (void __user *)arg, minsz)) > + if (copy_from_user(&op.err, (char __user *)arg + > + start, end - start)) So we trade 12 bytes of redundant copy for an extra stack variable and an arithmetic operation, not necessarily an obvious win, but more correct I guess. Alexey, I also notice that these 12 bytes means that the u64 fields in struct vfio_eeh_pe_err are not 8-byte aligned which could lead to compiler dependent packing interpretation issues with userspace. Should there be a 4-byte reserved field in there to make it explicit (so long as it matches the current interpretation)? Thanks, Alex