From 75255574498fad12727529c4ecbd4ccdabe86839 Mon Sep 17 00:00:00 2001 From: Ladi Prosek Date: Wed, 5 Oct 2016 17:22:26 +0200 Subject: [PATCH 4/8] balloon: fix segfault and harden the stats queue RH-Author: Ladi Prosek Message-id: <1475666548-9186-5-git-send-email-lprosek@redhat.com> Patchwork-id: 72483 O-Subject: [RHEL-7.4 qemu-kvm v2 PATCH 4/6] balloon: fix segfault and harden the stats queue Bugzilla: 1393484 RH-Acked-by: Paolo Bonzini RH-Acked-by: Michael S. Tsirkin RH-Acked-by: Stefan Hajnoczi The segfault here is triggered by the driver notifying the stats queue twice after adding a buffer to it. This effectively resets stats_vq_elem back to NULL and QEMU crashes on the next stats timer tick in balloon_stats_poll_cb. This is a regression introduced in 51b19ebe4320f3dc, although admittedly the device assumed too much about the stats queue protocol even before that commit. This commit adds a few more checks and ensures that the one stats buffer gets deallocated on device reset. Cc: qemu-stable@nongnu.org Signed-off-by: Ladi Prosek Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin (cherry picked from commit 4eae2a657d1ff5ada56eb9b4966eae0eff333b0b) Signed-off-by: Ladi Prosek Signed-off-by: Miroslav Rezanina Conflicts: * 1.5.3 does not return pointers from virtqueue_pop so only the "harden the stats queue" part of the upstream patch description applies * a new field stats_vq_elem_pending is introduced to keep track of the state of stats_vq_elem in lieu of its nullness upstream * virtio_balloon_device_reset only resets stats_vq_elem_pending because there is nothing to free --- hw/virtio/virtio-balloon.c | 27 +++++++++++++++++++++++---- include/hw/virtio/virtio-balloon.h | 1 + 2 files changed, 24 insertions(+), 4 deletions(-) diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index 016dc60..17b3029 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -95,13 +95,14 @@ static void balloon_stats_poll_cb(void *opaque) VirtIOBalloon *s = opaque; VirtIODevice *vdev = VIRTIO_DEVICE(s); - if (!balloon_stats_supported(s)) { + if (!s->stats_vq_elem_pending || !balloon_stats_supported(s)) { /* re-schedule */ balloon_stats_change_timer(s, s->stats_poll_interval); return; } virtqueue_push(s->svq, &s->stats_vq_elem, s->stats_vq_offset); + s->stats_vq_elem_pending = false; virtio_notify(vdev, s->svq); } @@ -220,14 +221,22 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq) static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq) { VirtIOBalloon *s = VIRTIO_BALLOON(vdev); - VirtQueueElement *elem = &s->stats_vq_elem; + VirtQueueElement elem; VirtIOBalloonStat stat; size_t offset = 0; qemu_timeval tv; - if (!virtqueue_pop(vq, elem)) { + if (!virtqueue_pop(vq, &elem)) { goto out; } + if (s->stats_vq_elem_pending) { + /* This should never happen if the driver follows the spec. */ + virtqueue_push(vq, &s->stats_vq_elem, 0); + virtio_notify(vdev, vq); + } + + s->stats_vq_elem = elem; + s->stats_vq_elem_pending = true; /* Initialize the stats to get rid of any stale values. This is only * needed to handle the case where a guest supports fewer stats than it @@ -235,7 +244,7 @@ static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq) */ reset_stats(s); - while (iov_to_buf(elem->out_sg, elem->out_num, offset, &stat, sizeof(stat)) + while (iov_to_buf(elem.out_sg, elem.out_num, offset, &stat, sizeof(stat)) == sizeof(stat)) { uint16_t tag = tswap16(stat.tag); uint64_t val = tswap64(stat.val); @@ -384,6 +393,15 @@ static void virtio_balloon_device_exit(VirtIODevice *vdev) virtio_cleanup(vdev); } +static void virtio_balloon_device_reset(VirtIODevice *vdev) +{ + VirtIOBalloon *s = VIRTIO_BALLOON(vdev); + + if (s->stats_vq_elem_pending) { + s->stats_vq_elem_pending = false; + } +} + static Property virtio_balloon_properties[] = { DEFINE_PROP_END_OF_LIST(), }; @@ -396,6 +414,7 @@ static void virtio_balloon_class_init(ObjectClass *klass, void *data) set_bit(DEVICE_CATEGORY_MISC, dc->categories); vdc->init = virtio_balloon_device_init; vdc->exit = virtio_balloon_device_exit; + vdc->reset = virtio_balloon_device_reset; vdc->get_config = virtio_balloon_get_config; vdc->set_config = virtio_balloon_set_config; vdc->get_features = virtio_balloon_get_features; diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h index f863bfe..a84736b 100644 --- a/include/hw/virtio/virtio-balloon.h +++ b/include/hw/virtio/virtio-balloon.h @@ -63,6 +63,7 @@ typedef struct VirtIOBalloon { uint32_t actual; uint64_t stats[VIRTIO_BALLOON_S_NR]; VirtQueueElement stats_vq_elem; + bool stats_vq_elem_pending; size_t stats_vq_offset; QEMUTimer *stats_timer; int64_t stats_last_update; -- 1.8.3.1