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=-7.0 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 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 072C3C2BA19 for ; Mon, 6 Apr 2020 13:55:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BFD2E21D79 for ; Mon, 6 Apr 2020 13:55:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FKO6nZ4/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728514AbgDFNzd (ORCPT ); Mon, 6 Apr 2020 09:55:33 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:53476 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728446AbgDFNzd (ORCPT ); Mon, 6 Apr 2020 09:55:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586181331; 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=4JbffD6uHYn0Xws8gEnJhH/ASm7vL5TTpW7bpIjfQF0=; b=FKO6nZ4/z3L/WVcnS5lXJgx77phqfkvab8uAbXMvYjU3DVbE/MwnF0N19jcAifVEBqXINj vGG0q7tuJBoK2OJJI2lN43I3m+RT1954LciLKCh8YWu4mmb4N2Hw/768QPgf7EUnMq2iRp Cs0raJx4VO5f6zzOrT/af1K4tRQhWwk= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-400--U-sHeqqNUySlH474rquSw-1; Mon, 06 Apr 2020 09:55:30 -0400 X-MC-Unique: -U-sHeqqNUySlH474rquSw-1 Received: by mail-wm1-f72.google.com with SMTP id f8so4926185wmh.4 for ; Mon, 06 Apr 2020 06:55:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=4JbffD6uHYn0Xws8gEnJhH/ASm7vL5TTpW7bpIjfQF0=; b=Hujp5Mnh5cLTjRlizRYYBvc9W4xJGPQO83FtKM1ud82P8GSC8uaZE732A4t/i2l97s ytMVsqM5MEY/zAIH6Pha2Eyqb50m3CADuKYeuMHbOfumNaRwOx5BGvv9Fdg741CD+cyQ CBbqO9qgr9WOt/PqurR3Rj5rSTzTZavWjqyB0g6gbtkaogrBPnFcZVYdBHpQjfCokBpt o0jUepq0Ddy3zd0s2hI6Y17OYdgHRchJL9S6XMVYc7v0gXGNt9N2jSOIbB82aZ102PFX xYqzlJXklwEuZY/dgqk5nv0a9KOpgdf9S3id/nEhRjNeYo9wNZlsh2un89kyS5NKCyoN Cz3A== X-Gm-Message-State: AGi0PuYuuB1glTUVWDM/GrDywvEaw3mFUuwwkWa43OXgIyiruJ8cn+AY cdt0Q60pwBsvyp8v9hT4kkl26Rzoo4656D1P0Gt/gvWF6aCrtfkmb3IR45xTHxCZcFLsWKuTQxH EALOQh0iTRbnMBNBbC9YvyW2g X-Received: by 2002:a5d:4d09:: with SMTP id z9mr602255wrt.292.1586181328771; Mon, 06 Apr 2020 06:55:28 -0700 (PDT) X-Google-Smtp-Source: APiQypJMOX8DPPm6vlwNHfWsSuz0mrVkzWpGk7TU+nZhYELINvwWAIdcv57+eCeK2DYp6J7Z3YNU5w== X-Received: by 2002:a5d:4d09:: with SMTP id z9mr602237wrt.292.1586181328553; Mon, 06 Apr 2020 06:55:28 -0700 (PDT) Received: from redhat.com (bzq-79-176-51-222.red.bezeqint.net. [79.176.51.222]) by smtp.gmail.com with ESMTPSA id w204sm25954947wma.1.2020.04.06.06.55.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 06:55:28 -0700 (PDT) Date: Mon, 6 Apr 2020 09:55:25 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH] vhost: force spec specified alignment on types Message-ID: <20200406095424-mutt-send-email-mst@kernel.org> References: <20200406124931.120768-1-mst@redhat.com> <045c84ed-151e-a850-9c72-5079bd2775e6@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <045c84ed-151e-a850-9c72-5079bd2775e6@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 06, 2020 at 09:34:00PM +0800, Jason Wang wrote: > > On 2020/4/6 下午8:50, 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=apcs-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 problematic > for the userspace that is using old uapi headers? > > Thanks It's not a problem in userspace. The problem is when userspace/guest uses 2 byte alignment and passes it to kernel assuming 8 byte alignment. The fix is for host not to make these assumptions. > > > > > 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]; > > struct vhost_desc *descs; > > diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_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[]; > > }; > > -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]) > > +/* > > + * The ring element addresses are passed between components with different > > + * alignments assumptions. Thus, we might need to decrease the compiler-selected > > + * alignment, and so must use a typedef to make sure the __aligned attribute > > + * actually takes hold: > > + * > > + * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-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 attribute must > > + * be specified as well. When used as part of a typedef, the aligned attribute > > + * 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_SIZE))) > > + 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, void *p, > > unsigned long align) > > {