[v2] vfio/common: Check iova with limit not with size

In vfio_listener_region_add(), the code makes sure
that the offset in the section is lower than the size
of the section.
But the calculation uses size of the region instead of
the region's limit (size - 1).

This leads to Int128 overflow when the region has
been initialized to UINT64_MAX because in this case
memory_region_init() transform the size from UINT64_MAX
to int128_2_64().

Let's really use the limit by sustracting one to the size
and take care to use the limit for functions using limit
and size to call functions which need size.

Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
---
 hw/vfio/common.c |   15 ++++++++++-----
 1 files changed, 10 insertions(+), 5 deletions(-)

On Tue, 2016-01-05 at 17:03 +0100, Pierre Morel wrote:
> In vfio_listener_region_add(), the code makes sure
> that the offset in the section is lower than the size
> of the section.
> But the calculation uses size of the region instead of
> the region's limit (size - 1).

We're really just trying to validate that the region is not zero sized
and hasn't overflowed the addresses space.

> This leads to Int128 overflow when the region has
> been initialized to UINT64_MAX because in this case
> memory_region_init() transform the size from UINT64_MAX
> to int128_2_64().
> 
> Let's really use the limit by sustracting one to the size
> and take care to use the limit for functions using limit
> and size to call functions which need size.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
> ---
>  hw/vfio/common.c |   15 ++++++++++-----
>  1 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 6797208..fe4962a 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -342,18 +342,23 @@ static void vfio_listener_region_add(MemoryListener *listener,
>  
>      iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
>      llend = int128_make64(section->offset_within_address_space);
> -    llend = int128_add(llend, section->size);
> +
> +    if (int128_ge(llend, int128_2_64())) {

We've just set llend using int128_make64, so this is guaranteed false.

> +        llend = int128_add(llend, int128_sub(section->size, int128_one()));
> +    } else {
> +        llend = int128_add(llend, section->size);
> +    }

So the above changed nothing.

>      llend = int128_and(llend, int128_exts64(TARGET_PAGE_MASK));
>  
> -    if (int128_ge(int128_make64(iova), llend)) {
> +    if (int128_gt(int128_make64(iova), llend)) {

And this allows zero sized regions through.

>          return;
>      }
>      end = int128_get64(llend);
>  
> -    if ((iova < container->min_iova) || ((end - 1) > container->max_iova)) {
> +    if ((iova < container->min_iova) || (end > container->max_iova)) {
>          error_report("vfio: IOMMU container %p can't map guest IOVA region"
>                       " 0x%"HWADDR_PRIx"..0x%"HWADDR_PRIx,
> -                     container, iova, end - 1);
> +                     container, iova, end);

This looks wrong too, max_iova is set to the last valid iova, for
instance if the iommu only supported a 4k address space, max_iova would
be 0xfff.  A mapping of size 4k at offset 0 should work, but this
change would cause it to fail.

>          ret = -EFAULT;
>          goto fail;
>      }
> @@ -363,7 +368,7 @@ static void vfio_listener_region_add(MemoryListener *listener,
>      if (memory_region_is_iommu(section->mr)) {
>          VFIOGuestIOMMU *giommu;
>  
> -        trace_vfio_listener_region_add_iommu(iova, end - 1);
> +        trace_vfio_listener_region_add_iommu(iova, end);
>          /*
>           * FIXME: We should do some checking to see if the
>           * capabilities of the host VFIO IOMMU are adequate to model

I think maybe you want to set end using:

end = int128_get64(int128_sub(llend, int128_one()));

Then removing the -1 in other places becomes correct, BUT we need to
add 1 where we're passing the size, end - iova - > end - iova + 1.
 Thanks,

Alex

On 01/06/2016 08:08 PM, Alex Williamson wrote:
> On Tue, 2016-01-05 at 17:03 +0100, Pierre Morel wrote:
>> In vfio_listener_region_add(), the code makes sure
>> that the offset in the section is lower than the size
>> of the section.
>> But the calculation uses size of the region instead of
>> the region's limit (size - 1).
> We're really just trying to validate that the region is not zero sized
> and hasn't overflowed the addresses space.
>
>> This leads to Int128 overflow when the region has
>> been initialized to UINT64_MAX because in this case
>> memory_region_init() transform the size from UINT64_MAX
>> to int128_2_64().
>>
>> Let's really use the limit by sustracting one to the size
>> and take care to use the limit for functions using limit
>> and size to call functions which need size.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
>> ---
>>   hw/vfio/common.c |   15 ++++++++++-----
>>   1 files changed, 10 insertions(+), 5 deletions(-)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 6797208..fe4962a 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -342,18 +342,23 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>   
>>       iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
>>       llend = int128_make64(section->offset_within_address_space);
>> -    llend = int128_add(llend, section->size);
>> +
>> +    if (int128_ge(llend, int128_2_64())) {
> We've just set llend using int128_make64, so this is guaranteed false.

hum, sorry, indeed.

>
>> +        llend = int128_add(llend, int128_sub(section->size, int128_one()));
>> +    } else {
>> +        llend = int128_add(llend, section->size);
>> +    }
> So the above changed nothing.
>
>>       llend = int128_and(llend, int128_exts64(TARGET_PAGE_MASK));
>>   
>> -    if (int128_ge(int128_make64(iova), llend)) {
>> +    if (int128_gt(int128_make64(iova), llend)) {
> And this allows zero sized regions through.
>
>>           return;
>>       }
>>       end = int128_get64(llend);
>>   
>> -    if ((iova < container->min_iova) || ((end - 1) > container->max_iova)) {
>> +    if ((iova < container->min_iova) || (end > container->max_iova)) {
>>           error_report("vfio: IOMMU container %p can't map guest IOVA region"
>>                        " 0x%"HWADDR_PRIx"..0x%"HWADDR_PRIx,
>> -                     container, iova, end - 1);
>> +                     container, iova, end);
> This looks wrong too, max_iova is set to the last valid iova, for
> instance if the iommu only supported a 4k address space, max_iova would
> be 0xfff.  A mapping of size 4k at offset 0 should work, but this
> change would cause it to fail.
>
>>           ret = -EFAULT;
>>           goto fail;
>>       }
>> @@ -363,7 +368,7 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>       if (memory_region_is_iommu(section->mr)) {
>>           VFIOGuestIOMMU *giommu;
>>   
>> -        trace_vfio_listener_region_add_iommu(iova, end - 1);
>> +        trace_vfio_listener_region_add_iommu(iova, end);
>>           /*
>>            * FIXME: We should do some checking to see if the
>>            * capabilities of the host VFIO IOMMU are adequate to model
> I think maybe you want to set end using:
>
> end = int128_get64(int128_sub(llend, int128_one()));
>
> Then removing the -1 in other places becomes correct, BUT we need to
> add 1 where we're passing the size, end - iova - > end - iova + 1.
>   Thanks,
>
> Alex
>

You are right, I try again.

Pierre