Re: [PATCH] vfio: fix VFIO_IOMMU_UNMAP_DMA when end of range would overflow u64

Alejandro Jimenez
2025-10-07T14:47:07Z

On 10/7/25 7:48 AM, Jason Gunthorpe wrote:
> On Mon, Oct 06, 2025 at 09:23:56PM -0400, Alejandro Jimenez wrote:
>
>> I mentioned this issue on the cover letter for:
>> https://lore.kernel.org/qemu-devel/20250919213515.917111-1-alejandro.j.jimenez@oracle.com/
>
> Use iommufd for this kind of work?
>

ACK, need to test with iommufd as well.

>> I mentioned in the notes for the patch above why I chose a slightly more
>> complex method than the '- 1' approach, since there is a chance that
>> iova+size could also go beyond the end of the address space and actually
>> wrap around.
>
> At the uapi boundary it should check that size != 0 and
> !check_add_overflow(iova+size). It is much easier to understand if the
> input from userspace is validated immediately at userspace.
>
> Then the rest of the code safely computes the last with 'iova+size-1'
> and does range logic based on last not end.
>

Makes sense, just thought adding overflow detection/resiliency in the
rest of the code is not that complex and provides an additional safety.

Thank you,
Alejandro

> Jason