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=-8.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 EEEEFC2BA19 for ; Mon, 6 Apr 2020 13:34:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BEBE02332B for ; Mon, 6 Apr 2020 13:34:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BvPejWvF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728474AbgDFNeN (ORCPT ); Mon, 6 Apr 2020 09:34:13 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:49966 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728319AbgDFNeN (ORCPT ); Mon, 6 Apr 2020 09:34:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586180051; h=from:from: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=8Vgo7PmY6XRwUGwyUrdIW6ngf/mYRofULc4TfPkTyZY=; b=BvPejWvF62X0MSz4WOnQPwDCcuOdqhbs17F7VAiAlgvk+sl+hntau1izK/X+iXgXT63dDQ JQ72OCE8HVjs2mmWWlWCHhZfONUFW0GctMevBxMWGs26leDam6C0XSx3BQYZhI2U8hnmCX cLUbsdHzt13NLPucFe+sAChNF4Dry4s= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-57-OOOB-UXuOJGo5RROJLVUvg-1; Mon, 06 Apr 2020 09:34:07 -0400 X-MC-Unique: OOOB-UXuOJGo5RROJLVUvg-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6C015801E5C; Mon, 6 Apr 2020 13:34:06 +0000 (UTC) Received: from [10.72.12.191] (ovpn-12-191.pek2.redhat.com [10.72.12.191]) by smtp.corp.redhat.com (Postfix) with ESMTP id AD718B19CB; Mon, 6 Apr 2020 13:34:01 +0000 (UTC) Subject: Re: [PATCH] vhost: force spec specified alignment on types To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org References: <20200406124931.120768-1-mst@redhat.com> From: Jason Wang Message-ID: <045c84ed-151e-a850-9c72-5079bd2775e6@redhat.com> Date: Mon, 6 Apr 2020 21:34:00 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200406124931.120768-1-mst@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/4/6 =E4=B8=8B=E5=8D=888:50, Michael S. Tsirkin wrote: > The ring element addresses are passed between components with different > alignments assumptions. Thus, if guest/userspace selects a pointer and > host then gets and dereferences it, we might need to decrease the > compiler-selected alignment to prevent compiler on the host from > assuming pointer is aligned. > > This actually triggers on ARM with -mabi=3Dapcs-gnu - which is a > deprecated configuration, but it seems safer to handle this > generally. > > I verified that the produced binary is exactly identical on x86. > > Signed-off-by: Michael S. Tsirkin > --- > > This is my preferred way to handle the ARM incompatibility issues > (in preference to kconfig hacks). > I will push this into next now. > Comments? I'm not sure if it's too late to fix. It would still be still=20 problematic for the userspace that is using old uapi headers? Thanks > > drivers/vhost/vhost.h | 6 ++--- > include/uapi/linux/virtio_ring.h | 41 ++++++++++++++++++++++++-------= - > 2 files changed, 34 insertions(+), 13 deletions(-) > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index cc82918158d2..a67bda9792ec 100644 > --- a/drivers/vhost/vhost.h > +++ b/drivers/vhost/vhost.h > @@ -74,9 +74,9 @@ struct vhost_virtqueue { > /* The actual ring of buffers. */ > struct mutex mutex; > unsigned int num; > - struct vring_desc __user *desc; > - struct vring_avail __user *avail; > - struct vring_used __user *used; > + vring_desc_t __user *desc; > + vring_avail_t __user *avail; > + vring_used_t __user *used; > const struct vhost_iotlb_map *meta_iotlb[VHOST_NUM_ADDRS]; > =20 > struct vhost_desc *descs; > diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virt= io_ring.h > index 559f42e73315..cd6e0b2eaf2f 100644 > --- a/include/uapi/linux/virtio_ring.h > +++ b/include/uapi/linux/virtio_ring.h > @@ -118,16 +118,6 @@ struct vring_used { > struct vring_used_elem ring[]; > }; > =20 > -struct vring { > - unsigned int num; > - > - struct vring_desc *desc; > - > - struct vring_avail *avail; > - > - struct vring_used *used; > -}; > - > /* Alignment requirements for vring elements. > * When using pre-virtio 1.0 layout, these fall out naturally. > */ > @@ -164,6 +154,37 @@ struct vring { > #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) > #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)-= >num]) > =20 > +/* > + * The ring element addresses are passed between components with diffe= rent > + * alignments assumptions. Thus, we might need to decrease the compile= r-selected > + * alignment, and so must use a typedef to make sure the __aligned att= ribute > + * actually takes hold: > + * > + * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Com= mon-Type-Attributes > + * > + * When used on a struct, or struct member, the aligned attribute can = only > + * increase the alignment; in order to decrease it, the packed attribu= te must > + * be specified as well. When used as part of a typedef, the aligned a= ttribute > + * can both increase and decrease alignment, and specifying the packed > + * attribute generates a warning. > + */ > +typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE= ))) > + vring_desc_t; > +typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SI= ZE))) > + vring_avail_t; > +typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE= ))) > + vring_used_t; > + > +struct vring { > + unsigned int num; > + > + vring_desc_t *desc; > + > + vring_avail_t *avail; > + > + vring_used_t *used; > +}; > + > static inline void vring_init(struct vring *vr, unsigned int num, voi= d *p, > unsigned long align) > {