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?
>
> 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
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