Re: [PATCH 3/3] iommu/uapi: Add helper function for size lookup

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 28 Jan 2020 22:02:04 -0800
Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:

> IOMMU UAPI can be extended in the future by adding new
> fields at the end of each user data structure. Since we use
> a unified UAPI version for compatibility checking, a lookup
> function is needed to find the correct user data size to copy
> from user.
> 
> This patch adds a helper function based on a 2D lookup with
> version and type as input arguments.
> 
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>  drivers/iommu/iommu.c | 22 ++++++++++++++++++++++
>  include/linux/iommu.h |  6 ++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 7dd51c5d2ba1..9e5de9abebdf 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1696,6 +1696,28 @@ int iommu_sva_unbind_gpasid(struct iommu_domain *domain, struct device *dev,
>  }
>  EXPORT_SYMBOL_GPL(iommu_sva_unbind_gpasid);
>  
> +
> +/**
> + * Maintain a UAPI version to user data structure size lookup for each
> + * API function types we support. e.g. bind guest pasid, cache invalidation.
> + * As data structures being extended with new members, the offsetofend()
> + * will identify the new sizes.
> + */
> +const static int iommu_uapi_data_size[NR_IOMMU_UAPI_TYPE][IOMMU_UAPI_VERSION] = {
> +	/* IOMMU_UAPI_BIND_GPASID */
> +	{offsetofend(struct iommu_gpasid_bind_data, vtd)},
> +	/* IOMMU_UAPI_CACHE_INVAL */
> +	{offsetofend(struct iommu_cache_invalidate_info, addr_info)},
> +	/* IOMMU_UAPI_PAGE_RESP */
> +	{offsetofend(struct iommu_page_response, code)},
> +};
> +
> +int iommu_uapi_get_data_size(int type, int version)
> +{

Seems like this is asking for a bounds check,

  if (type >= NR_IOMMU_UAPI_TYPE || version > IOMMU_UAPI_VERSION)
  	return -EINVAL;

If we add new types in future versions, I assume we'd back fill the
table with -EINVAL as well (rather than zero).  Thanks,

Alex

> +	return iommu_uapi_data_size[type][version - 1];
> +}
> +EXPORT_SYMBOL_GPL(iommu_uapi_get_data_size);
> +
>  static void __iommu_detach_device(struct iommu_domain *domain,
>  				  struct device *dev)
>  {
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 9718c109ea0a..416fe02160ba 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -500,6 +500,7 @@ extern int iommu_report_device_fault(struct device *dev,
>  				     struct iommu_fault_event *evt);
>  extern int iommu_page_response(struct device *dev,
>  			       struct iommu_page_response *msg);
> +extern int iommu_uapi_get_data_size(int type, int version);
>  
>  extern int iommu_group_id(struct iommu_group *group);
>  extern struct iommu_group *iommu_group_get_for_dev(struct device *dev);
> @@ -885,6 +886,11 @@ static inline int iommu_page_response(struct device *dev,
>  	return -ENODEV;
>  }
>  
> +static int iommu_uapi_get_data_size(int type, int version)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline int iommu_group_id(struct iommu_group *group)
>  {
>  	return -ENODEV;