On Tue, Oct 29, 2024 at 11:49:07AM -0300, Jason Gunthorpe wrote:
> On Fri, Oct 25, 2024 at 04:49:43PM -0700, Nicolin Chen wrote:
> > To support driver-allocated vIOMMU objects, it's suggested to call the
> > allocator helper in IOMMU dirvers. However, there is no guarantee that
> > drivers will all use it and allocate objects properly.
> >
> > Add a helper for iommufd core to verify if an unfinalized object is at
> > least reserved in the ictx.
>
> I don't think we need this..
>
> iommufd_object_finalize() already does:
>
> old = xa_store(&ictx->objects, obj->id, obj, GFP_KERNEL);
> /* obj->id was returned from xa_alloc() so the xa_store() cannot fail */
> WARN_ON(old);
It feels unsafe to carry on the iommufd_viommu_alloc_ioctl() until
iommufd_object_finalize() as the function would touch the returned
faulty viommu pointer? E.g. what if the viommu has an even smaller
size than struct iommufd_viommu?
> So, we could enhance it to be more robust, like this patch is doing:
>
> void iommufd_object_finalize(struct iommufd_ctx *ictx,
> struct iommufd_object *obj)
> {
> void *old;
>
> old = xa_cmpxchg(&ictx->objects, obj->id, XA_ZERO_ENTRY, obj,
> GFP_KERNEL);
> /* obj->id was returned from xa_alloc() so the xa_store() cannot fail */
> WARN_ON(old != XA_ZERO_ENTRY);
>
> It is always a driver bug to not initialize that object, so WARN_ON is
> OK.
I think we'd need the same change in iommufd_object_abort() too.
Thanks
Nicolin
