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

[Jason Wang]

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 <address@hidden>
>> Cc: Petr Matousek <address@hidden>
>> Signed-off-by: Jason Wang <address@hidden>
> 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.
>
>> ---
>>  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