Re: [PATCH v3 4/5] iommu/uapi: Handle data and argsz filled by users

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Jacob,

On 2020/6/24 1:03, Jacob Pan wrote:
> IOMMU UAPI data has a user filled argsz field which indicates the data
> length comes with the API call. User data is not trusted, argsz must be
> validated based on the current kernel data size, mandatory data size,
> and feature flags.
> 
> User data may also be extended, results in possible argsz increase.
> Backward compatibility is ensured based on size and flags checking.
> Details are documented in Documentation/userspace-api/iommu.rst
> 
> This patch adds sanity checks in both IOMMU layer and vendor code, where
> VT-d is the only user for now.
> 
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>   drivers/iommu/intel/svm.c |  3 ++
>   drivers/iommu/iommu.c     | 96 ++++++++++++++++++++++++++++++++++++++++++++---
>   include/linux/iommu.h     |  7 ++--
>   3 files changed, 98 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index 713b3a218483..237db56878c0 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -244,6 +244,9 @@ int intel_svm_bind_gpasid(struct iommu_domain *domain, struct device *dev,
>   	    data->format != IOMMU_PASID_FORMAT_INTEL_VTD)
>   		return -EINVAL;
>   
> +	if (data->argsz != offsetofend(struct iommu_gpasid_bind_data, vendor.vtd))
> +		return -EINVAL;

Need to do size check in intel_iommu_sva_invalidate() as well?

> +
>   	if (!dev_is_pci(dev))
>   		return -ENOTSUPP;
>   
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index d43120eb1dc5..4a025c429b41 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1951,22 +1951,108 @@ int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
>   EXPORT_SYMBOL_GPL(iommu_attach_device);
>   
>   int iommu_cache_invalidate(struct iommu_domain *domain, struct device *dev,
> -			   struct iommu_cache_invalidate_info *inv_info)
> +			void __user *uinfo)

Nit: keep it aligned.

>   {
> +	struct iommu_cache_invalidate_info inv_info;
> +	unsigned long minsz, maxsz;
> +
>   	if (unlikely(!domain->ops->cache_invalidate))
>   		return -ENODEV;
>   
> -	return domain->ops->cache_invalidate(domain, dev, inv_info);
> +	/* Current kernel data size is the max to be copied from user */
> +	maxsz = sizeof(struct iommu_cache_invalidate_info);
> +	memset((void *)&inv_info, 0, maxsz);
> +
> +	/*
> +	 * No new spaces can be added before the variable sized union, the
> +	 * minimum size is the offset to the union.
> +	 */
> +	minsz = offsetof(struct iommu_cache_invalidate_info, granu);
> +
> +	/* Copy minsz from user to get flags and argsz */
> +	if (copy_from_user(&inv_info, uinfo, minsz))
> +		return -EFAULT;
> +
> +	/* Fields before variable size union is mandatory */
> +	if (inv_info.argsz < minsz)
> +		return -EINVAL;
> +	/*
> +	 * User might be using a newer UAPI header, we shall let IOMMU vendor
> +	 * driver decide on what size it needs. Since the UAPI data extension
> +	 * can be vendor specific, larger argsz could be the result of extension
> +	 * for one vendor but it should not affect another vendor.
> +	 */
> +	/*
> +	 * User might be using a newer UAPI header which has a larger data
> +	 * size, we shall support the existing flags within the current
> +	 * size.
> +	 */
> +	if (inv_info.argsz > maxsz)
> +		inv_info.argsz = maxsz;
> +
> +	/* Checking the exact argsz based on generic flags */
> +	if (inv_info.granularity == IOMMU_INV_GRANU_ADDR &&
> +		inv_info.argsz != offsetofend(struct iommu_cache_invalidate_info,
> +					granu.addr_info))
> +		return -EINVAL;
> +
> +	if (inv_info.granularity == IOMMU_INV_GRANU_PASID &&
> +		inv_info.argsz != offsetofend(struct iommu_cache_invalidate_info,
> +					granu.pasid_info))
> +		return -EINVAL;
> +
> +	/* Copy the remaining user data _after_ minsz */
> +	if (copy_from_user((void *)&inv_info + minsz, uinfo + minsz,
> +				inv_info.argsz - minsz))
> +		return -EFAULT;
> +
> +	return domain->ops->cache_invalidate(domain, dev, &inv_info);
>   }
>   EXPORT_SYMBOL_GPL(iommu_cache_invalidate);
>   
> -int iommu_sva_bind_gpasid(struct iommu_domain *domain,
> -			   struct device *dev, struct iommu_gpasid_bind_data *data)
> +int iommu_sva_bind_gpasid(struct iommu_domain *domain, struct device *dev,
> +						void __user *udata)
>   {
> +
> +	struct iommu_gpasid_bind_data data;
> +	unsigned long minsz, maxsz;
> +
>   	if (unlikely(!domain->ops->sva_bind_gpasid))
>   		return -ENODEV;
>   
> -	return domain->ops->sva_bind_gpasid(domain, dev, data);
> +	/* Current kernel data size is the max to be copied from user */
> +	maxsz = sizeof(struct iommu_gpasid_bind_data);
> +	memset((void *)&data, 0, maxsz);
> +
> +	/*
> +	 * No new spaces can be added before the variable sized union, the
> +	 * minimum size is the offset to the union.
> +	 */
> +	minsz = offsetof(struct iommu_gpasid_bind_data, vendor);
> +
> +	/* Copy minsz from user to get flags and argsz */
> +	if (copy_from_user(&data, udata, minsz))
> +		return -EFAULT;
> +
> +	/* Fields before variable size union is mandatory */
> +	if (data.argsz < minsz)
> +		return -EINVAL;
> +	/*
> +	 * User might be using a newer UAPI header, we shall let IOMMU vendor
> +	 * driver decide on what size it needs. Since the guest PASID bind data
> +	 * can be vendor specific, larger argsz could be the result of extension
> +	 * for one vendor but it should not affect another vendor.
> +	 */
> +	if (data.argsz > maxsz)
> +		data.argsz = maxsz;
> +
> +	/* Copy the remaining user data _after_ minsz */
> +	if (copy_from_user((void *)&data + minsz, udata + minsz,
> +				data.argsz - minsz))
> +		return -EFAULT;
> +
> +
> +	return domain->ops->sva_bind_gpasid(domain, dev, &data);
>   }
>   EXPORT_SYMBOL_GPL(iommu_sva_bind_gpasid);
>   
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 5f0b7859d2eb..a688fea42ae5 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -432,9 +432,10 @@ extern void iommu_detach_device(struct iommu_domain *domain,
>   				struct device *dev);
>   extern int iommu_cache_invalidate(struct iommu_domain *domain,
>   				  struct device *dev,
> -				  struct iommu_cache_invalidate_info *inv_info);
> +				  void __user *uinfo);
> +
>   extern int iommu_sva_bind_gpasid(struct iommu_domain *domain,
> -		struct device *dev, struct iommu_gpasid_bind_data *data);
> +				struct device *dev, void __user *udata);
>   extern int iommu_sva_unbind_gpasid(struct iommu_domain *domain,
>   				struct device *dev, ioasid_t pasid);
>   extern struct iommu_domain *iommu_get_domain_for_dev(struct device *dev);
> @@ -1062,7 +1063,7 @@ iommu_cache_invalidate(struct iommu_domain *domain,
>   	return -ENODEV;
>   }
>   static inline int iommu_sva_bind_gpasid(struct iommu_domain *domain,
> -				struct device *dev, struct iommu_gpasid_bind_data *data)
> +				struct device *dev, void __user *udata)
>   {
>   	return -ENODEV;
>   }
> 

Best regards,
baolu
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