Re: [PATCH] vhost/vdpa: reject overflowing PA map page counts

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

On Wed, Jun 24, 2026 at 09:06:53PM +0200, 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. If that addition wraps,
> the code can pin and map fewer pages than the requested IOTLB range.
> 
> Reject sizes that overflow the page-count calculation.

You should add "on 32 bit systems" - I do not see how it can
overflow on 64 bit.

> Also make the
> memlock check subtraction-based so a large page count cannot wrap the
> pinned page total.

I don't see how this can happen at all - pinned_vm is in units of pages.

> Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
> ---
>  drivers/vhost/vdpa.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index ac55275fa..090cb8693 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -1102,6 +1102,8 @@ 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 pinned_vm;
>  	u64 start = iova;
>  	long pinned;
>  	int ret = 0;
> @@ -1114,7 +1116,12 @@ 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;
> @@ -1123,7 +1130,8 @@ static int vhost_vdpa_pa_map(struct vhost_vdpa *v,
>  	mmap_read_lock(dev->mm);
>  
>  	lock_limit = PFN_DOWN(rlimit(RLIMIT_MEMLOCK));
> -	if (npages + atomic64_read(&dev->mm->pinned_vm) > lock_limit) {
> +	pinned_vm = atomic64_read(&dev->mm->pinned_vm);
> +	if (npages > lock_limit || pinned_vm > lock_limit - npages) {
>  		ret = -ENOMEM;
>  		goto unlock;
>  	}
> -- 
> 2.54.0