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=-6.7 required=3.0 tests=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 98A89C76192 for ; Wed, 17 Jul 2019 11:33:14 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 73D4C20880 for ; Wed, 17 Jul 2019 11:33:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 73D4C20880 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56152 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hniBN-0005UR-8x for qemu-devel@archiver.kernel.org; Wed, 17 Jul 2019 07:33:13 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45289) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hniAz-0004Xk-AV for qemu-devel@nongnu.org; Wed, 17 Jul 2019 07:32:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hniAx-0008QO-Vy for qemu-devel@nongnu.org; Wed, 17 Jul 2019 07:32:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58450) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hniAx-0008Ps-NI; Wed, 17 Jul 2019 07:32:47 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D805185539; Wed, 17 Jul 2019 11:32:46 +0000 (UTC) Received: from redhat.com (ovpn-120-247.rdu2.redhat.com [10.10.120.247]) by smtp.corp.redhat.com (Postfix) with SMTP id 229AE1001B18; Wed, 17 Jul 2019 11:32:39 +0000 (UTC) Date: Wed, 17 Jul 2019 07:32:38 -0400 From: "Michael S. Tsirkin" To: David Hildenbrand Message-ID: <20190717072934-mutt-send-email-mst@kernel.org> References: <20190717084255.17173-1-david@redhat.com> <20190717054727-mutt-send-email-mst@kernel.org> <5a5d6f86-04f2-4e61-473c-d8a4b0ed5045@redhat.com> <5d50ddb0-b1ac-0bd1-6466-6e605b804809@redhat.com> <20190717070323-mutt-send-email-mst@kernel.org> <737c3d80-b9e1-6280-a6e6-f7aee139a3b9@redhat.com> <20190717072053-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 17 Jul 2019 11:32:46 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH-for-4.1] virtio-balloon: fix QEMU crashes on pagesize > BALLOON_PAGE_SIZE X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Igor Mammedov , David Gibson , qemu-devel@nongnu.org, Stefan Hajnoczi , qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 17, 2019 at 01:28:19PM +0200, David Hildenbrand wrote: > On 17.07.19 13:22, Michael S. Tsirkin wrote: > > On Wed, Jul 17, 2019 at 01:10:21PM +0200, David Hildenbrand wrote: > >> On 17.07.19 13:06, Michael S. Tsirkin wrote: > >>> On Wed, Jul 17, 2019 at 12:17:57PM +0200, David Hildenbrand wrote: > >>>> On 17.07.19 12:04, David Hildenbrand wrote: > >>>>> On 17.07.19 11:57, Michael S. Tsirkin wrote: > >>>>>> On Wed, Jul 17, 2019 at 10:42:55AM +0200, David Hildenbrand wrote: > >>>>>>> We are using the wrong functions to set/clear bits, effectively touching > >>>>>>> multiple bits, writing out of range of the bitmap, resulting in memory > >>>>>>> corruptions. We have to use set_bit()/clear_bit() instead. > >>>>>>> > >>>>>>> Can easily be reproduced by starting a qemu guest on hugetlbfs memory, > >>>>>>> inflating the balloon. QEMU crashes. This never could have worked > >>>>>>> properly - especially, also pages would have been discarded when the > >>>>>>> first sub-page would be inflated (the whole bitmap would be set). > >>>>>>> > >>>>>>> While testing I realized, that on hugetlbfs it is pretty much impossible > >>>>>>> to discard a page - the guest just frees the 4k sub-pages in random order > >>>>>>> most of the time. I was only able to discard a hugepage a handful of > >>>>>>> times - so I hope that now works correctly. > >>>>>>> > >>>>>>> Fixes: ed48c59875b6 ("virtio-balloon: Safely handle BALLOON_PAGE_SIZE < > >>>>>>> host page size") > >>>>>>> Fixes: b27b32391404 ("virtio-balloon: Fix possible guest memory corruption > >>>>>>> with inflates & deflates") > >>>>>>> Cc: qemu-stable@nongnu.org #v4.0.0 > >>>>>>> Cc: Stefan Hajnoczi > >>>>>>> Cc: David Gibson > >>>>>>> Cc: Michael S. Tsirkin > >>>>>>> Cc: Igor Mammedov > >>>>>>> Signed-off-by: David Hildenbrand > >>>>>>> --- > >>>>>>> hw/virtio/virtio-balloon.c | 10 ++++------ > >>>>>>> 1 file changed, 4 insertions(+), 6 deletions(-) > >>>>>>> > >>>>>>> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > >>>>>>> index e85d1c0d5c..669067d661 100644 > >>>>>>> --- a/hw/virtio/virtio-balloon.c > >>>>>>> +++ b/hw/virtio/virtio-balloon.c > >>>>>>> @@ -94,9 +94,8 @@ static void balloon_inflate_page(VirtIOBalloon *balloon, > >>>>>>> balloon->pbp->base = host_page_base; > >>>>>>> } > >>>>>>> > >>>>>>> - bitmap_set(balloon->pbp->bitmap, > >>>>>>> - (ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>>>>>> - subpages); > >>>>>>> + set_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>>>>>> + balloon->pbp->bitmap); > >>>>>>> > >>>>>>> if (bitmap_full(balloon->pbp->bitmap, subpages)) { > >>>>>>> /* We've accumulated a full host page, we can actually discard > >>>>>>> @@ -140,9 +139,8 @@ static void balloon_deflate_page(VirtIOBalloon *balloon, > >>>>>>> * for a guest to do this in practice, but handle it anyway, > >>>>>>> * since getting it wrong could mean discarding memory the > >>>>>>> * guest is still using. */ > >>>>>>> - bitmap_clear(balloon->pbp->bitmap, > >>>>>>> - (ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>>>>>> - subpages); > >>>>>>> + clear_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>>>>>> + balloon->pbp->bitmap); > >>>>>>> > >>>>>>> if (bitmap_empty(balloon->pbp->bitmap, subpages)) { > >>>>>>> g_free(balloon->pbp); > >>>>>> > >>>>>> I also started to wonder about this: > >>>>>> > >>>>>> if (!balloon->pbp) { > >>>>>> /* Starting on a new host page */ > >>>>>> size_t bitlen = BITS_TO_LONGS(subpages) * sizeof(unsigned long); > >>>>>> balloon->pbp = g_malloc0(sizeof(PartiallyBalloonedPage) + bitlen); > >>>>>> balloon->pbp->rb = rb; > >>>>>> balloon->pbp->base = host_page_base; > >>>>>> } > >>>>>> > >>>>>> Is keeping a pointer to a ram block like this safe? what if the ramblock > >>>>>> gets removed? > >>>>>> > >>>>> > >>>>> David added > >>>>> > >>>>> if (balloon->pbp > >>>>> && (rb != balloon->pbp->rb ) ... > >>>>> > >>>>> So in case the rb changes (IOW replaced - delete old one, new one > >>>>> added), we reset the data. > >>>>> > >>>>> After a ram block was deleted, there will be no more deflation requests > >>>>> coming in for it. This should be fine I guess. > >>> > >>> I think it might happen that an old dangling pointer happens > >>> to match a newly allocated one. > >>> I think we really should just cache all data we want to take into account > >>> and compare that. > >> > >> That's true. I think just remembering and comparing the GPA base address > >> would be sufficient. > > > > Well we need to know the bitmap size allocated, too. > > And I guess when we are ready to free we should > > re-check it just in case. > > Right, either that or the page size, which is orthogonal. > > > > >> However, I don't consider this here to trigger easily. We would need > >> some crazy memory unplug+replug going on while using the balloon. So I > >> assume we can just rework this part after 4.1 > > > > Dangling pointers are just a recipe for CVEs. I'd rather rework it now. > > > > If they are not dereferences, I don't consider it an ultimate problem. The following pattern is highly unsafe if p has been freed and reused: if (d->p == p) use p->foo and this is because we can now have copies of d->p->foo != p->foo resulting in inconsistencies. > But yeah, I'll look into that tomorrow. Can you pick up these patches in > the meantime? > > Thanks! Sure, thanks! > -- > > Thanks, > > David / dhildenb