Re: [PATCH v3 09/17] iommufd: Add IOMMU_HWPT_INVALIDATE

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Jul 31, 2023 at 10:19:09AM -0300, Jason Gunthorpe wrote:
> On Mon, Jul 31, 2023 at 10:07:32AM +0000, Liu, Yi L wrote:
> > > > +		goto out_put_hwpt;
> > > > +	}
> > > > +
> > > > +	/*
> > > > +	 * Copy the needed fields before reusing the ucmd buffer, this
> > > > +	 * avoids memory allocation in this path.
> > > > +	 */
> > > > +	user_ptr = cmd->data_uptr;
> > > > +	user_data_len = cmd->data_len;
> > > 
> > > Uhh, who checks that klen < the temporary stack struct?
> > 
> > Take vtd as an example. The invalidate structure is struct iommu_hwpt_vtd_s1_invalidate[1].
> > The klen is sizeof(struct iommu_hwpt_vtd_s1_invalidate)[2]. iommu_hwpt_vtd_s1_invalidate
> > is also placed in the temporary stack struct (actually it is a union)[1]. So the klen should
> > be <= temporary stack.
> 
> Ohh, I think I would add a few comments noting that the invalidate
> structs need to be added to that union. Easy to miss.

Added here:

-        * Copy the needed fields before reusing the ucmd buffer, this
-        * avoids memory allocation in this path.
+        * Copy the needed fields before reusing the ucmd buffer, this avoids
+        * memory allocation in this path. Again, user invalidate data struct
+        * must be added to the union ucmd_buffer.

> > It's not so explicit though. Perhaps worth to have a check like below in this patch?
> > 
> > if (unlikely(klen > sizeof(union ucmd_buffer)))
> > 	return -EINVAL;
> 
> Yes, stick this in the domain allocate path with a WARN_ON. The driver
> is broken to allocate a domain with an invalid size.

And here too with a WARN_ON_ONCE.

+       /*
+        * Either the driver is broken by having an invalid size, or the user
+        * invalidate data struct used by the driver is missing in the union.
+        */
+       if (WARN_ON_ONCE(hwpt->domain->ops->cache_invalidate_user &&
+                        (!hwpt->domain->ops->cache_invalidate_user_data_len ||
+                         hwpt->domain->ops->cache_invalidate_user_data_len >
+                         sizeof(union ucmd_buffer)))) {
+               rc = -EINVAL;
+               goto out_abort;
+
+       }

Though I am making this cache_invalidate_user optional here, I
wonder if there actually could be a case that a user-managed
domain doesn't need a cache_invalidate_user op...

Thanks
Nicolin