On Mon, Mar 27, 2017 at 12:02:33PM +0200, Ladi Prosek wrote: > On Fri, Mar 24, 2017 at 9:59 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Fri, Mar 24, 2017 at 09:40:07PM +0100, Arnd Bergmann wrote: > >> On Fri, Mar 24, 2017 at 9:11 PM, Ladi Prosek <lprosek@xxxxxxxxxx> wrote: > >> > On Fri, Mar 24, 2017 at 7:38 PM, David Hildenbrand <david@xxxxxxxxxx> 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 <arnd@xxxxxxxx> > >> >>> --- > >> >>> 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? > > I will do it. If we go the route of returning 'idx' from > update_balloon_stats, my patch > > virtio_balloon: don't push uninitialized buffers to stats virtqueue > > needs to be redone anyway. Thanks! Can you do it soon pls? I'd like to do a pull request. > >> 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 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization