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

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Message-ID: <aOWa6yD0oyQSgFTW@devgpu015.cco6.facebook.com>
Date: Tue, 7 Oct 2025 15:57:47 -0700
From: Alex Mastro <amastro@...com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>,
        Jason Gunthorpe
	<jgg@...pe.ca>, <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 Tue, Oct 07, 2025 at 02:43:28PM -0600, Alex Williamson wrote:
> I prefer this approach, thanks for tackling it.  Consider splitting
> into a few patches for easier review, ex. discrete input sanitizing with
> proper overflow checking, refactoring the fast/slow handlers to
> increment iova in the caller, remainder to tie it all together.  A few
> comments inline below. 

Alright -- I'll try to stage incrementally. The proposed sequencing sgtm.

> > +	u64 end, to_pin;
> 
> end looks like a dma_addr_t and to_pin ought to be a size_t, right?
> Maybe iova_end and iova_size?

Yes, I think I've been sloppy with the types. Am too 64-bit oriented.

> > -	if (!iommu || !pages)
> > +	if (!iommu || !pages || npage < 0)
> >  		return -EINVAL;
> >  
> >  	/* Supported for v2 version only */
> >  	if (!iommu->v2)
> >  		return -EACCES;
> >  
> > +	if (npage == 0)
> > +		return 0;
> > +
> > +	if (check_mul_overflow(npage, PAGE_SIZE, &to_pin))
> > +		return -EINVAL;
> > +
> > +	if (check_add_overflow(user_iova, to_pin - 1, &end))
> > +		return -EINVAL;
> > +
> 
> Why not the same checks on vfio_iommu_type1_unpin_pages()?

Will see if there's opportunity to stay more consistent.

> >  				if (WARN_ON(!phys)) {
> > -					iova += PAGE_SIZE;
> > +					pos += PAGE_SIZE;
> >  					continue;
> >  				}
> >  
> > +
> 
> Extra white space

Ack.

> >  				size = PAGE_SIZE;
> >  				p = phys + size;
> >  				i = iova + size;
> > -				while (i < dma->iova + dma->size &&
> > +				while (size + pos < dma->size &&
> >  				       p == iommu_iova_to_phys(d->domain, i)) {
> >  					size += PAGE_SIZE;
> >  					p += PAGE_SIZE;
> 
> I think the else branch after this has some use cases too, (iova -
> dma->iova) just becomes 'pos' in calculating vaddr, 'n' should be
> calculated as (dma->size - pos).

Missed this simplification - thanks.

> > +		u64 end;
> 
> Seems like a dma_addr_t.  range_end?  Thanks,

Ack