Re: [PATCH v6 5/6] iommu/uapi: Handle data and argsz filled by users

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

On Thu, 23 Jul 2020 10:25:39 -0700
Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:

> IOMMU user APIs are responsible for processing user data. This patch
> changes the interface such that user pointers can be passed into IOMMU
> code directly. Separate kernel APIs without user pointers are introduced
> for in-kernel users of the UAPI functionality.
> 
> IOMMU UAPI data has a user filled argsz field which indicates the data
> length of the structure. 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, resulting in possible argsz increase.
> Backward compatibility is ensured based on size and flags (or
> the functional equivalent fields) checking.
> 
> This patch adds sanity checks in the IOMMU layer. In addition to argsz,
> reserved/unused fields in padding, flags, and version are also checked.
> Details are documented in Documentation/userspace-api/iommu.rst
> 
> 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 | 202 ++++++++++++++++++++++++++++++++++++++++++++++++--
>  include/linux/iommu.h |  28 ++++---
>  2 files changed, 213 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 3a913ce94a3d..1ce2a61058c6 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1950,33 +1950,219 @@ int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(iommu_attach_device);
>  
> +/*
> + * Check flags and other user provided data for valid combinations. We also
> + * make sure no reserved fields or unused flags are set. This is to ensure
> + * not breaking userspace in the future when these fields or flags are used.
> + */
> +static int iommu_check_cache_invl_data(struct iommu_cache_invalidate_info *info)
> +{
> +	u32 mask;
> +	int i;
> +
> +	if (info->version != IOMMU_CACHE_INVALIDATE_INFO_VERSION_1)
> +		return -EINVAL;
> +
> +	mask = (1 << IOMMU_CACHE_INV_TYPE_NR) - 1;
> +	if (info->cache & ~mask)
> +		return -EINVAL;
> +
> +	if (info->granularity >= IOMMU_INV_GRANU_NR)
> +		return -EINVAL;
> +
> +	switch (info->granularity) {
> +	case IOMMU_INV_GRANU_ADDR:
> +		if (info->cache & IOMMU_CACHE_INV_TYPE_PASID)
> +			return -EINVAL;
> +
> +		mask = IOMMU_INV_ADDR_FLAGS_PASID |
> +			IOMMU_INV_ADDR_FLAGS_ARCHID |
> +			IOMMU_INV_ADDR_FLAGS_LEAF;
> +
> +		if (info->granu.addr_info.flags & ~mask)
> +			return -EINVAL;
> +		break;
> +	case IOMMU_INV_GRANU_PASID:
> +		mask = IOMMU_INV_PASID_FLAGS_PASID |
> +			IOMMU_INV_PASID_FLAGS_ARCHID;
> +		if (info->granu.pasid_info.flags & ~mask)
> +			return -EINVAL;
> +
> +		break;
> +	case IOMMU_INV_GRANU_DOMAIN:
> +		if (info->cache & IOMMU_CACHE_INV_TYPE_DEV_IOTLB)
> +			return -EINVAL;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	/* Check reserved padding fields */
> +	for (i = 0; i < 6; i++) {

We could use sizeof(info->padding) here to avoid future issues relative
to the number of padding bytes.

> +		if (info->padding[i])
> +			return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  int iommu_uapi_cache_invalidate(struct iommu_domain *domain, struct device *dev,
> -				struct iommu_cache_invalidate_info *inv_info)
> +				void __user *uinfo)
>  {
> +	struct iommu_cache_invalidate_info inv_info = { 0 };
> +	u32 minsz;
> +	int ret = 0;
> +
>  	if (unlikely(!domain->ops->cache_invalidate))
>  		return -ENODEV;
>  
> -	return domain->ops->cache_invalidate(domain, dev, inv_info);
> +	/*
> +	 * 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;
> +
> +	/* PASID and address granu require additional info beyond minsz */
> +	if (inv_info.argsz == minsz &&
> +	    ((inv_info.granularity == IOMMU_INV_GRANU_PASID) ||
> +		    (inv_info.granularity == IOMMU_INV_GRANU_ADDR)))
> +		return -EINVAL;
> +
> +	if (inv_info.granularity == IOMMU_INV_GRANU_PASID &&
> +	    inv_info.argsz < offsetofend(struct iommu_cache_invalidate_info, granu.pasid_info))
> +		return -EINVAL;
> +
> +	if (inv_info.granularity == IOMMU_INV_GRANU_ADDR &&
> +	    inv_info.argsz < offsetofend(struct iommu_cache_invalidate_info, granu.addr_info))
> +		return -EINVAL;
> +
> +	/*
> +	 * User might be using a newer UAPI header which has a larger data
> +	 * size, we shall support the existing flags within the current
> +	 * size. Copy the remaining user data _after_ minsz but not more
> +	 * than the current kernel supported size.
> +	 */
> +	if (copy_from_user((void *)&inv_info + minsz, uinfo + minsz,
> +			   min(inv_info.argsz, (u32)sizeof(inv_info)) - minsz))

Could use min_t() to cast both args to the specified type.

> +		return -EFAULT;
> +
> +	/* Now the argsz is validated, check the content */
> +	ret = iommu_check_cache_invl_data(&inv_info);
> +	if (ret)
> +		return ret;
> +
> +	return domain->ops->cache_invalidate(domain, dev, &inv_info);
>  }
>  EXPORT_SYMBOL_GPL(iommu_uapi_cache_invalidate);
>  
> -int iommu_uapi_sva_bind_gpasid(struct iommu_domain *domain,
> -			       struct device *dev, struct iommu_gpasid_bind_data *data)
> +static int iommu_check_bind_data(struct iommu_gpasid_bind_data *data)
> +{
> +	u32 mask;
> +	int i;
> +
> +	if (data->version != IOMMU_GPASID_BIND_VERSION_1)
> +		return -EINVAL;
> +
> +	/* Check all supported format, for now just VT-d */
> +	mask = IOMMU_PASID_FORMAT_INTEL_VTD;
> +	if (data->format & ~mask)

data->format is not a bitmask though, it's an index, right?  Should
defined formats be put into an enum with a last entry place holder for
this code to test against?  If we end up with holes in the enum, I
guess we'd need to use special cases, ex:

switch (data->format) {
	case IOMMU_PASID_FORMAT_DEPRECATED0:
		return -EINVAL;
	case 0 ... IOMMU_PASID_FORMAT_LAST:
		break;
	default:
		return -EINVAL;
}

It seems strange and error prone anyway for common code to check
against a specific vendor format here.

> +		return -EINVAL;
> +
> +	/* Check all flags */
> +	mask = IOMMU_SVA_GPASID_VAL;
> +	if (data->flags & ~mask)
> +		return -EINVAL;
> +
> +	/* Check reserved padding fields */
> +	for (i = 0; i < 8; i++) {

sizeof(data->padding)

> +		if (data->padding[i])
> +			return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int iommu_sva_prepare_bind_data(void __user *udata,
> +				       struct iommu_gpasid_bind_data *data)
>  {
> +	u32 minsz;
> +
> +	/*
> +	 * 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.
> +	 * Copy the remaining user data _after_ minsz
> +	 */
> +	if (copy_from_user((void *)data + minsz, udata + minsz,
> +			   min(data->argsz, (u32)sizeof(*data)) - minsz))

min_t() here too.  Thanks,

Alex

> +		return -EFAULT;
> +
> +	return iommu_check_bind_data(data);
> +}
> +
> +int iommu_uapi_sva_bind_gpasid(struct iommu_domain *domain, struct device *dev,
> +			       void __user *udata)
> +{
> +	struct iommu_gpasid_bind_data data = { 0 };
> +	int ret;
> +
>  	if (unlikely(!domain->ops->sva_bind_gpasid))
>  		return -ENODEV;
>  
> -	return domain->ops->sva_bind_gpasid(domain, dev, data);
> +	ret = iommu_sva_prepare_bind_data(udata, &data);
> +	if (ret)
> +		return ret;
> +
> +	return domain->ops->sva_bind_gpasid(domain, dev, &data);
>  }
>  EXPORT_SYMBOL_GPL(iommu_uapi_sva_bind_gpasid);
>  
> -int iommu_uapi_sva_unbind_gpasid(struct iommu_domain *domain, struct device *dev,
> -				 ioasid_t pasid)
> +int iommu_sva_unbind_gpasid(struct iommu_domain *domain, struct device *dev,
> +			    struct iommu_gpasid_bind_data *data)
>  {
>  	if (unlikely(!domain->ops->sva_unbind_gpasid))
>  		return -ENODEV;
>  
> -	return domain->ops->sva_unbind_gpasid(dev, pasid);
> +	return domain->ops->sva_unbind_gpasid(dev, data->hpasid);
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_unbind_gpasid);
> +
> +int iommu_uapi_sva_unbind_gpasid(struct iommu_domain *domain, struct device *dev,
> +				 void __user *udata)
> +{
> +	struct iommu_gpasid_bind_data data = { 0 };
> +	int ret;
> +
> +	if (unlikely(!domain->ops->sva_bind_gpasid))
> +		return -ENODEV;
> +
> +	ret = iommu_sva_prepare_bind_data(udata, &data);
> +	if (ret)
> +		return ret;
> +
> +	return iommu_sva_unbind_gpasid(domain, dev, &data);
>  }
>  EXPORT_SYMBOL_GPL(iommu_uapi_sva_unbind_gpasid);
>  
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 2dcc1a33f6dc..4a02c9e09048 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -432,11 +432,14 @@ extern void iommu_detach_device(struct iommu_domain *domain,
>  				struct device *dev);
>  extern int iommu_uapi_cache_invalidate(struct iommu_domain *domain,
>  				       struct device *dev,
> -				       struct iommu_cache_invalidate_info *inv_info);
> +				       void __user *uinfo);
> +
>  extern int iommu_uapi_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_uapi_sva_unbind_gpasid(struct iommu_domain *domain,
> -					struct device *dev, ioasid_t pasid);
> +					struct device *dev, void __user *udata);
> +extern int iommu_sva_unbind_gpasid(struct iommu_domain *domain,
> +				   struct device *dev, struct iommu_gpasid_bind_data *data);
>  extern struct iommu_domain *iommu_get_domain_for_dev(struct device *dev);
>  extern struct iommu_domain *iommu_get_dma_domain(struct device *dev);
>  extern int iommu_map(struct iommu_domain *domain, unsigned long iova,
> @@ -1054,22 +1057,29 @@ static inline int iommu_sva_get_pasid(struct iommu_sva *handle)
>  	return IOMMU_PASID_INVALID;
>  }
>  
> -static inline int iommu_uapi_cache_invalidate(struct iommu_domain *domain,
> -					      struct device *dev,
> -					      struct iommu_cache_invalidate_info *inv_info)
> +static inline int
> +iommu_uapi_cache_invalidate(struct iommu_domain *domain,
> +			    struct device *dev,
> +			    struct iommu_cache_invalidate_info *inv_info)
>  {
>  	return -ENODEV;
>  }
>  
>  static inline int iommu_uapi_sva_bind_gpasid(struct iommu_domain *domain,
> -					     struct device *dev,
> -					     struct iommu_gpasid_bind_data *data)
> +					     struct device *dev, void __user *udata)
>  {
>  	return -ENODEV;
>  }
>  
>  static inline int iommu_uapi_sva_unbind_gpasid(struct iommu_domain *domain,
> -					       struct device *dev, int pasid)
> +					       struct device *dev, void __user *udata)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline int iommu_sva_unbind_gpasid(struct iommu_domain *domain,
> +					  struct device *dev,
> +					  struct iommu_gpasid_bind_data *data)
>  {
>  	return -ENODEV;
>  }