From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936154AbdCXU7r (ORCPT ); Fri, 24 Mar 2017 16:59:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43842 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936107AbdCXU7i (ORCPT ); Fri, 24 Mar 2017 16:59:38 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com BCAB9C04B31F Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=mst@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com BCAB9C04B31F Date: Fri, 24 Mar 2017 23:59:35 +0300 From: "Michael S. Tsirkin" To: Arnd Bergmann Cc: Ladi Prosek , David Hildenbrand , Jason Wang , Yisheng Xie , Konstantin Neumoin , Linux Kernel Mailing List , virtualization@lists.linux-foundation.org, Minchan Kim , "Denis V. Lunev" , Andrew Morton , Ingo Molnar Subject: Re: [PATCH] virtio_balloon: prevent uninitialized variable use Message-ID: <20170324235900-mutt-send-email-mst@kernel.org> References: <20170323151728.679684-1-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Fri, 24 Mar 2017 20:59:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 24, 2017 at 09:40:07PM +0100, Arnd Bergmann wrote: > On Fri, Mar 24, 2017 at 9:11 PM, Ladi Prosek wrote: > > On Fri, Mar 24, 2017 at 7:38 PM, David Hildenbrand wrote: > >> On 23.03.2017 16:17, Arnd Bergmann wrote: > >>> The latest gcc-7.0.1 snapshot reports a new warning: > >>> > >>> virtio/virtio_balloon.c: In function 'update_balloon_stats': > >>> virtio/virtio_balloon.c:258:26: error: 'events[2]' is used uninitialized in this function [-Werror=uninitialized] > >>> virtio/virtio_balloon.c:260:26: error: 'events[3]' is used uninitialized in this function [-Werror=uninitialized] > >>> virtio/virtio_balloon.c:261:56: error: 'events[18]' is used uninitialized in this function [-Werror=uninitialized] > >>> virtio/virtio_balloon.c:262:56: error: 'events[17]' is used uninitialized in this function [-Werror=uninitialized] > >>> > >>> This seems absolutely right, so we should add an extra check to > >>> prevent copying uninitialized stack data into the statistics. > >>> From all I can tell, this has been broken since the statistics code > >>> was originally added in 2.6.34. > >>> > >>> Fixes: 9564e138b1f6 ("virtio: Add memory statistics reporting to the balloon driver (V4)") > >>> Signed-off-by: Arnd Bergmann > >>> --- > >>> drivers/virtio/virtio_balloon.c | 2 ++ > >>> 1 file changed, 2 insertions(+) > >>> > >>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > >>> index 4e1191508228..cd5c54e2003d 100644 > >>> --- a/drivers/virtio/virtio_balloon.c > >>> +++ b/drivers/virtio/virtio_balloon.c > >>> @@ -254,12 +254,14 @@ static void update_balloon_stats(struct virtio_balloon *vb) > >>> > >>> available = si_mem_available(); > >>> > >>> +#ifdef CONFIG_VM_EVENT_COUNTERS > >>> update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN, > >>> pages_to_bytes(events[PSWPIN])); > >>> update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT, > >>> pages_to_bytes(events[PSWPOUT])); > >>> update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]); > >>> update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]); > >>> +#endif > >>> update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE, > >>> pages_to_bytes(i.freeram)); > >>> update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT, > > > > This will leave four uninitialized slots in vb->stats if > > CONFIG_VM_EVENT_COUNTERS is not defined. update_balloon_stats should > > have > > > > BUG_ON(idx < VIRTIO_BALLOON_S_NR); > > > > at the end. > > > > You need to make sure that vb->stats is smaller, either by using > > something else than VIRTIO_BALLOON_S_NR for its size or something else > > than sizeof(vb->stats) as the last argument to sg_init_one in this > > file. > > Ah, got it. Would one of you create a fixed patch for this, or should I? > > An easy way to solve it would be to preinitialize the events array > and return zeroes to the host, but I don't know if that's the right > solution. I think that's out of spec. > Another option would be to return 'idx' from update_balloon_stats, > and use that for the size: > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index cd5c54e2003d..bea3cfb88e53 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -242,7 +242,7 @@ static inline void update_stat(struct > virtio_balloon *vb, int idx, > > #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT) > > -static void update_balloon_stats(struct virtio_balloon *vb) > +static unsigned int update_balloon_stats(struct virtio_balloon *vb) > { > unsigned long events[NR_VM_EVENT_ITEMS]; > struct sysinfo i; > @@ -268,6 +268,8 @@ static void update_balloon_stats(struct virtio_balloon *vb) > pages_to_bytes(i.totalram)); > update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL, > pages_to_bytes(available)); > + > + return idx; > } > > /* > @@ -294,13 +296,14 @@ static void stats_handle_request(struct > virtio_balloon *vb) > struct virtqueue *vq; > struct scatterlist sg; > unsigned int len; > + unsigned int num_stats; > > - update_balloon_stats(vb); > + num_stats = update_balloon_stats(vb); > > vq = vb->stats_vq; > if (!virtqueue_get_buf(vq, &len)) > return; > - sg_init_one(&sg, vb->stats, sizeof(vb->stats)); > + sg_init_one(&sg, vb->stats, sizeof(vb->stats[0] * num_stats)); > virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); > virtqueue_kick(vq); > } > > Arnd Sounds reasonable. -- MST