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

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Message-ID: <96398096-ef62-4873-bf60-5b54026c5760@oracle.com>
Date: Tue, 7 Oct 2025 10:46:52 -0400
From: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Alex Mastro <amastro@...com>,
        Alex Williamson
 <alex.williamson@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio: fix VFIO_IOMMU_UNMAP_DMA when end of range would
 overflow u64



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