Re: [Qemu-devel] [PATCH 1/3] virtio-pci: properly validate address before accessing config

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Apr 28, 2013 at 03:54:20PM +0800, Jason Wang wrote:
> On 04/28/2013 03:26 AM, Michael S. Tsirkin wrote:
> > On Fri, Apr 26, 2013 at 04:34:02PM +0800, Jason Wang wrote:
> >> There are several several issues in the current checking:
> >>
> >> - The check was based on the minus of unsigned values which can overflow
> >> - It was done after .{set|get}_config() which can lead crash when config_len is
> >>   zero since vdev->config is NULL
> >>
> >> Fix this by:
> >>
> >> - Validate the address in virtio_pci_config_{read|write}() before
> >>   .{set|get}_config
> >> - Use addition instead minus to do the validation
> >>
> >> Cc: Michael S. Tsirkin <mst@redhat.com>
> >> Cc: Petr Matousek <pmatouse@redhat.com>
> >> Signed-off-by: Jason Wang <jasowang@redhat.com>
> > Why do this in virtio-pci and not in virtio.c?
> > If instead we correct the checks in virtio.c we
> > get less code, and all transports will benefit
> > automatically.
> 
> I wish I could but looks like vitio_config_read{b|w|l} were only used by
> virtio-pci. Other transport such as ccw and s390-virtio-bus have their
> own implementation.

Okay but still, the bug is in checks in virtio.c, why not fix it there
instead of making it assume caller does the checks?

> >
> >> ---
> >>  hw/virtio/virtio-pci.c |    9 +++++++++
> >>  hw/virtio/virtio.c     |   18 ------------------
> >>  2 files changed, 9 insertions(+), 18 deletions(-)
> >>
> >> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> >> index a1f15a8..7f6c7d1 100644
> >> --- a/hw/virtio/virtio-pci.c
> >> +++ b/hw/virtio/virtio-pci.c
> >> @@ -400,6 +400,10 @@ static uint64_t virtio_pci_config_read(void *opaque, hwaddr addr,
> >>      }
> >>      addr -= config;
> >>  
> >> +    if (addr + size > proxy->vdev->config_len) {
> >> +        return (uint32_t)-1;
> >> +    }
> >> +
> >>      switch (size) {
> >>      case 1:
> >>          val = virtio_config_readb(proxy->vdev, addr);
> >> @@ -430,6 +434,11 @@ static void virtio_pci_config_write(void *opaque, hwaddr addr,
> >>          return;
> >>      }
> >>      addr -= config;
> >> +
> >> +    if (addr + size > proxy->vdev->config_len) {
> >> +        return;
> >> +    }
> >> +
> >>      /*
> >>       * Virtio-PCI is odd. Ioports are LE but config space is target native
> >>       * endian.
> >> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >> index 1c2282c..3397b5e 100644
> >> --- a/hw/virtio/virtio.c
> >> +++ b/hw/virtio/virtio.c
> >> @@ -563,9 +563,6 @@ uint32_t virtio_config_readb(VirtIODevice *vdev, uint32_t addr)
> >>  
> >>      vdev->get_config(vdev, vdev->config);
> >>  
> >> -    if (addr > (vdev->config_len - sizeof(val)))
> >> -        return (uint32_t)-1;
> >> -
> >>      val = ldub_p(vdev->config + addr);
> >>      return val;
> >>  }
> >> @@ -576,9 +573,6 @@ uint32_t virtio_config_readw(VirtIODevice *vdev, uint32_t addr)
> >>  
> >>      vdev->get_config(vdev, vdev->config);
> >>  
> >> -    if (addr > (vdev->config_len - sizeof(val)))
> >> -        return (uint32_t)-1;
> >> -
> >>      val = lduw_p(vdev->config + addr);
> >>      return val;
> >>  }
> >> @@ -589,9 +583,6 @@ uint32_t virtio_config_readl(VirtIODevice *vdev, uint32_t addr)
> >>  
> >>      vdev->get_config(vdev, vdev->config);
> >>  
> >> -    if (addr > (vdev->config_len - sizeof(val)))
> >> -        return (uint32_t)-1;
> >> -
> >>      val = ldl_p(vdev->config + addr);
> >>      return val;
> >>  }
> >> @@ -600,9 +591,6 @@ void virtio_config_writeb(VirtIODevice *vdev, uint32_t addr, uint32_t data)
> >>  {
> >>      uint8_t val = data;
> >>  
> >> -    if (addr > (vdev->config_len - sizeof(val)))
> >> -        return;
> >> -
> >>      stb_p(vdev->config + addr, val);
> >>  
> >>      if (vdev->set_config)
> >> @@ -613,9 +601,6 @@ void virtio_config_writew(VirtIODevice *vdev, uint32_t addr, uint32_t data)
> >>  {
> >>      uint16_t val = data;
> >>  
> >> -    if (addr > (vdev->config_len - sizeof(val)))
> >> -        return;
> >> -
> >>      stw_p(vdev->config + addr, val);
> >>  
> >>      if (vdev->set_config)
> >> @@ -626,9 +611,6 @@ void virtio_config_writel(VirtIODevice *vdev, uint32_t addr, uint32_t data)
> >>  {
> >>      uint32_t val = data;
> >>  
> >> -    if (addr > (vdev->config_len - sizeof(val)))
> >> -        return;
> >> -
> >>      stl_p(vdev->config + addr, val);
> >>  
> >>      if (vdev->set_config)
> >> -- 
> >> 1.7.1