On Tue, Feb 04, 2020 at 05:02:39PM +0100, Cornelia Huck wrote:
> On Tue, 4 Feb 2020 15:16:18 +0000
> Stefan Hajnoczi <stefa...@redhat.com> wrote:
>
> > hw/virtio.c checks vq->vring.desc != NULL to see if the vring has been
> > set up successfully.
> >
> > When virtio_queue_set_rings() fails due to an invalid vring memory
> > address it must clear vq->vring.desc (and related fields) so we don't
> > treat this virtqueue as successfully initialized later on.
> >
> > This bug was found by device fuzzing and can be triggered as follows:
> >
> > $ qemu -M pc -device virtio-blk-pci,id=drv0,drive=drive0,addr=4.0 \
> > -drive
> > if=none,id=drive0,file=null-co://,format=raw,auto-read-only=off \
> > -drive
> > if=none,id=drive1,file=null-co://,file.read-zeroes=on,format=raw \
> > -display none \
> > -qtest stdio
> > endianness
> > outl 0xcf8 0x80002020
> > outl 0xcfc 0xe0000000
> > outl 0xcf8 0x80002004
> > outw 0xcfc 0x7
> > write 0xe0000000 0x24
> > 0x00ffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffab5cffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffab0000000001
> > inb 0x4
> > writew 0xe000001c 0x1
> > write 0xe0000014 0x1 0x0d
> >
> > The following error message is produced:
> >
> > qemu-system-x86_64: /home/stefanha/qemu/hw/virtio/virtio.c:286:
> > vring_get_region_caches: Assertion `caches != NULL' failed.
> >
> > The backtrace looks like this:
> >
> > #0 0x00007ffff5520625 in raise () at /lib64/libc.so.6
> > #1 0x00007ffff55098d9 in abort () at /lib64/libc.so.6
> > #2 0x00007ffff55097a9 in _nl_load_domain.cold () at /lib64/libc.so.6
> > #3 0x00007ffff5518a66 in annobin_assert.c_end () at /lib64/libc.so.6
> > #4 0x00005555559073da in vring_get_region_caches (vq=<optimized out>) at
> > qemu/hw/virtio/virtio.c:286
> > #5 vring_get_region_caches (vq=<optimized out>) at
> > qemu/hw/virtio/virtio.c:283
> > #6 0x000055555590818d in vring_used_flags_set_bit (mask=1,
> > vq=0x5555575ceea0) at qemu/hw/virtio/virtio.c:398
> > #7 virtio_queue_split_set_notification (enable=0, vq=0x5555575ceea0) at
> > qemu/hw/virtio/virtio.c:398
> > #8 virtio_queue_set_notification (vq=vq@entry=0x5555575ceea0,
> > enable=enable@entry=0) at qemu/hw/virtio/virtio.c:451
> > #9 0x0000555555908512 in virtio_queue_set_notification
> > (vq=vq@entry=0x5555575ceea0, enable=enable@entry=0) at
> > qemu/hw/virtio/virtio.c:444
> > #10 0x00005555558c697a in virtio_blk_handle_vq (s=0x5555575c57e0,
> > vq=0x5555575ceea0) at qemu/hw/block/virtio-blk.c:775
> > #11 0x0000555555907836 in virtio_queue_notify_aio_vq (vq=0x5555575ceea0)
> > at qemu/hw/virtio/virtio.c:2244
> > #12 0x0000555555cb5dd7 in aio_dispatch_handlers
> > (ctx=ctx@entry=0x55555671a420) at util/aio-posix.c:429
> > #13 0x0000555555cb67a8 in aio_dispatch (ctx=0x55555671a420) at
> > util/aio-posix.c:460
> > #14 0x0000555555cb307e in aio_ctx_dispatch (source=<optimized out>,
> > callback=<optimized out>, user_data=<optimized out>) at util/async.c:260
> > #15 0x00007ffff7bbc510 in g_main_context_dispatch () at
> > /lib64/libglib-2.0.so.0
> > #16 0x0000555555cb5848 in glib_pollfds_poll () at util/main-loop.c:219
> > #17 os_host_main_loop_wait (timeout=<optimized out>) at
> > util/main-loop.c:242
> > #18 main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:518
> > #19 0x00005555559b20c9 in main_loop () at vl.c:1683
> > #20 0x0000555555838115 in main (argc=<optimized out>, argv=<optimized
> > out>, envp=<optimized out>) at vl.c:4441
> >
> > Reported-by: Alexander Bulekov <alx...@bu.edu>
> > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> > ---
> > hw/virtio/virtio.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 2c5410e981..5d7f619a1e 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -2163,6 +2163,11 @@ void virtio_queue_set_rings(VirtIODevice *vdev, int
> > n, hwaddr desc,
> > vdev->vq[n].vring.avail = avail;
> > vdev->vq[n].vring.used = used;
> > virtio_init_region_cache(vdev, n);
> > + if (vdev->broken) {
> > + vdev->vq[n].vring.desc = 0;
> > + vdev->vq[n].vring.avail = 0;
> > + vdev->vq[n].vring.used = 0;
> > + }
> > }
> >
> > void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
>
> This looks correct; but shouldn't virtio_queue_set_addr() also set
> .desc to 0 on failure?Now that you mention it, there are a number of other virtio_init_region_cache() callers that could be affected. I added the error handling code to virtio_queue_set_rings() because that's symmetric - this function sets .desc and so it should be the one to clear it on error. But now I think virtio_init_region_cache() should take on that responsibility so callers don't need to duplicate this error handling code. Stefan
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