On 07/13/2015 03:36 PM, Michael S. Tsirkin wrote: > On Mon, Jul 13, 2015 at 01:46:47PM +0800, Jason Wang wrote: >> We abort on unaligned read/write in >> virtio_address_space_read()/write() but since len in under control of >> guest so qemu will simply crash when booting a modern guest (guest is >> try to read when len is zero). >> read. > How can len be 0? Isn't this a guest bug? Or is this > a theoretical issue?
E.g cat /sys/bus/pci/devices/0000\:00\:03.0/config and also happen during boot (but not virtio specific code, probably pci core or something else). > >> Fix this by ignoring unaligned write or >> >> Fixes 1e40356ce5f6ccfa0bb57104a533c62952c560ce >> ("virtio fix cfg endian-ness for BE targets") >> Signed-off-by: Jason Wang <jasow...@redhat.com> > I guess since we ignore some illegal values (e.g. > 4) > we should just whitelist the legal ones. > So the following looks like a slightly cleaner way to > make this change. > > ---> > virtio-pci: don't crash on illegal length > > Some guests seem to access cfg with an illegal length value. > It's worth fixing them but debugging is easier if > qemu does not crash. > > Signed-off-by: Michael S. Tsirkin <m...@redhat.com> I believe when we can, we should avoid guest trigger-able abort. > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > index 6ca0258..c5e8cc0 100644 > --- a/hw/virtio/virtio-pci.c > +++ b/hw/virtio/virtio-pci.c > @@ -546,7 +546,8 @@ static void virtio_write_config(PCIDevice *pci_dev, > uint32_t address, > off = le32_to_cpu(cfg->cap.offset); > len = le32_to_cpu(cfg->cap.length); > > - if (len <= sizeof cfg->pci_cfg_data) { > + if (len == 1 || len == 2 || len == 4) { > + assert(len <= sizeof cfg->pci_cfg_data); > virtio_address_space_write(&proxy->modern_as, off, > cfg->pci_cfg_data, len); > } > @@ -570,7 +571,8 @@ static uint32_t virtio_read_config(PCIDevice *pci_dev, > off = le32_to_cpu(cfg->cap.offset); > len = le32_to_cpu(cfg->cap.length); > > - if (len <= sizeof cfg->pci_cfg_data) { > + if (len == 1 || len == 2 || len == 4) { > + assert(len <= sizeof cfg->pci_cfg_data); > virtio_address_space_read(&proxy->modern_as, off, > cfg->pci_cfg_data, len); > } >