Re: [PATCH v4] vhost/vdpa: reject overflowing PA map page counts on 32-bit

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 24, 2026 at 03:02:02PM -0700, Yousef Alhouseen wrote:
> vhost_vdpa_pa_map() adds the IOVA page offset to the user-controlled map
> size before computing the number of pages to pin. On 32-bit systems,
> where unsigned long is narrower than u64, that addition can overflow and
> the code can pin and map fewer pages than the requested IOTLB range.
> 
> Reject sizes that overflow the unsigned long page-count calculation.
> 
> Fixes: 22af48cf91aa ("vdpa: factor out vhost_vdpa_pa_map() and
> vhost_vdpa_pa_unmap()")

still 2 lines?

> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
> ---
> Changes in v4:
> - Keep the Fixes tag on one line.
> - Add Michael's Acked-by tag.
> 
> Changes in v3:
> - Add the Fixes tag.
> 
> Changes in v2:
> - Clarify that the overflow is on 32-bit systems.
> - Drop the unrelated memlock check change.
> 
>  drivers/vhost/vdpa.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index ac55275fa..38b28ed3d 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -1102,6 +1102,7 @@ static int vhost_vdpa_pa_map(struct vhost_vdpa *v,
>  	unsigned int gup_flags = FOLL_LONGTERM;
>  	unsigned long npages, cur_base, map_pfn, last_pfn = 0;
>  	unsigned long lock_limit, sz2pin, nchunks, i;
> +	unsigned long page_offset;
>  	u64 start = iova;
>  	long pinned;
>  	int ret = 0;
> @@ -1114,7 +1115,13 @@ static int vhost_vdpa_pa_map(struct vhost_vdpa *v,
>  	if (perm & VHOST_ACCESS_WO)
>  		gup_flags |= FOLL_WRITE;
> 
> -	npages = PFN_UP(size + (iova & ~PAGE_MASK));
> +	page_offset = iova & ~PAGE_MASK;
> +	if (size > ULONG_MAX - page_offset) {
> +		ret = -EINVAL;
> +		goto free;
> +	}
> +
> +	npages = PFN_UP(size + page_offset);
>  	if (!npages) {
>  		ret = -EINVAL;
>  		goto free;
> -- 
> 2.54.0