Re: [PATCH v4 2/9] iommu: Replace sva_iommu with iommu_attach_handle

[Jason Gunthorpe]

On Sun, Apr 28, 2024 at 06:22:28PM +0800, Baolu Lu wrote:

>         /* A bond already exists, just take a reference`. */
>         handle = iommu_attach_handle_get(group, iommu_mm->pasid);
>         if (handle) {
>                 if (handle->domain->iopf_handler != iommu_sva_iopf_handler)
> {
>                         ret = -EBUSY;
>                         goto out_unlock;
>                 }
> 
>                 refcount_inc(&handle->users);
>                 mutex_unlock(&iommu_sva_lock);
>                 return handle;
>         }
> 
> But it appears that this code is not lock safe. If the domain on the
> PASID is not a SVA domain, the check of "handle->domain->iopf_handler !=
> iommu_sva_iopf_handler" could result in a use-after-free issue as the
> other thread might detach the domain in between the fetch and check
> lines.

For the above you just need to pass in the iommu_sva_iopf_handler as
an argument to attach_handle_get() and have it check it under the
xa_lock.

The whole thing is already protected under the ugly sva_lock.

Ideally it would be protected by the group mutex..

Jason