Re: [PATCH RESEND 1/3] vfio/pci: fix a null pointer reference in vfio_rom_read

[Longpeng (Mike, Cloud Infrastructure Service Product Dept.)]

On 2020/2/25 0:04, Alex Williamson wrote:
> On Mon, 24 Feb 2020 14:42:17 +0800
> "Longpeng(Mike)" <address@hidden> wrote:
> 
>> From: Longpeng <address@hidden>
>>
>> vfio_pci_load_rom() maybe failed and then the vdev->rom is NULL in
>> some situation (though I've not encountered yet), maybe we should
>> avoid the VM abort.
>>
>> Signed-off-by: Longpeng <address@hidden>
>> ---
>>  hw/vfio/pci.c | 13 ++++++++-----
>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>> index 5e75a95..ed798ae 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -768,7 +768,7 @@ static void vfio_update_msi(VFIOPCIDevice *vdev)
>>      }
>>  }
>>  
>> -static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
>> +static bool vfio_pci_load_rom(VFIOPCIDevice *vdev)
>>  {
>>      struct vfio_region_info *reg_info;
>>      uint64_t size;
>> @@ -778,7 +778,7 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
>>      if (vfio_get_region_info(&vdev->vbasedev,
>>                               VFIO_PCI_ROM_REGION_INDEX, &reg_info)) {
>>          error_report("vfio: Error getting ROM info: %m");
>> -        return;
>> +        return false;
>>      }
>>  
>>      trace_vfio_pci_load_rom(vdev->vbasedev.name, (unsigned 
>> long)reg_info->size,
>> @@ -797,7 +797,7 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
>>          error_printf("Device option ROM contents are probably invalid "
>>                      "(check dmesg).\nSkip option ROM probe with rombar=0, "
>>                      "or load from file with romfile=\n");
>> -        return;
>> +        return false;
>>      }
>>  
>>      vdev->rom = g_malloc(size);
>> @@ -849,6 +849,8 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
>>              data[6] = -csum;
>>          }
>>      }
>> +
>> +    return true;
>>  }
>>  
>>  static uint64_t vfio_rom_read(void *opaque, hwaddr addr, unsigned size)
>> @@ -863,8 +865,9 @@ static uint64_t vfio_rom_read(void *opaque, hwaddr addr, 
>> unsigned size)
>>      uint64_t data = 0;
>>  
>>      /* Load the ROM lazily when the guest tries to read it */
>> -    if (unlikely(!vdev->rom && !vdev->rom_read_failed)) {
>> -        vfio_pci_load_rom(vdev);
>> +    if (unlikely(!vdev->rom && !vdev->rom_read_failed) &&
>> +        !vfio_pci_load_rom(vdev)) {
>> +        return 0;
>>      }
>>  
>>      memcpy(&val, vdev->rom + addr,
> 
> Looks like an obvious bug, until you look at the rest of this memcpy():
> 
> memcpy(&val, vdev->rom + addr,
>            (addr < vdev->rom_size) ? MIN(size, vdev->rom_size - addr) : 0);
> 
> IOW, we'll do a zero sized memcpy() if rom_size is zero, so there's no
> risk of the concern identified in the commit log.  This patch is
> unnecessary.  Thanks,
> 
Oh, I missed that, sorry for make the noise, thanks

> Alex
> 
> .
>