Re: [PATCH v2 13/13] vfio: powerpc/spapr: Enable Dynamic DMA windows

[Alex Williamson]

On Tue, 2014-09-23 at 13:01 +1000, Alexey Kardashevskiy wrote:
> This defines and implements VFIO IOMMU API which lets the userspace
> create and remove DMA windows.
> 
> This updates VFIO_IOMMU_SPAPR_TCE_GET_INFO to return the number of
> available windows and page mask.
> 
> This adds VFIO_IOMMU_SPAPR_TCE_CREATE and VFIO_IOMMU_SPAPR_TCE_REMOVE
> to allow the user space to create and remove window(s).
> 
> The VFIO IOMMU driver does basic sanity checks and calls corresponding
> SPAPR TCE functions. At the moment only IODA2 (POWER8 PCI host bridge)
> implements them.
> 
> This advertises VFIO_IOMMU_SPAPR_TCE_FLAG_DDW capability via
> VFIO_IOMMU_SPAPR_TCE_GET_INFO.
> 
> This calls platform DDW reset() callback when IOMMU is being disabled
> to reset the DMA configuration to its original state.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c | 135 ++++++++++++++++++++++++++++++++++--
>  include/uapi/linux/vfio.h           |  25 ++++++-
>  2 files changed, 153 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 0dccbc4..b518891 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -190,18 +190,25 @@ static void tce_iommu_disable(struct tce_container *container)
>  
>  	container->enabled = false;
>  
> -	if (!container->grp || !current->mm)
> +	if (!container->grp)
>  		return;
>  
>  	data = iommu_group_get_iommudata(container->grp);
>  	if (!data || !data->iommu_owner || !data->ops->get_table)
>  		return;
>  
> -	tbl = data->ops->get_table(data, 0);
> -	if (!tbl)
> -		return;
> +	if (current->mm) {
> +		tbl = data->ops->get_table(data, 0);
> +		if (tbl)
> +			decrement_locked_vm(tbl);
>  
> -	decrement_locked_vm(tbl);
> +		tbl = data->ops->get_table(data, 1);
> +		if (tbl)
> +			decrement_locked_vm(tbl);
> +	}
> +
> +	if (data->ops->reset)
> +		data->ops->reset(data);
>  }
>  
>  static void *tce_iommu_open(unsigned long arg)
> @@ -243,7 +250,7 @@ static long tce_iommu_ioctl(void *iommu_data,
>  				 unsigned int cmd, unsigned long arg)
>  {
>  	struct tce_container *container = iommu_data;
> -	unsigned long minsz;
> +	unsigned long minsz, ddwsz;
>  	long ret;
>  
>  	switch (cmd) {
> @@ -288,6 +295,28 @@ static long tce_iommu_ioctl(void *iommu_data,
>  		info.dma32_window_size = tbl->it_size << tbl->it_page_shift;
>  		info.flags = 0;
>  
> +		ddwsz = offsetofend(struct vfio_iommu_spapr_tce_info,
> +				page_size_mask);
> +
> +		if (info.argsz == ddwsz) {

>=

> +			if (data->ops->query && data->ops->create &&
> +					data->ops->remove) {
> +				info.flags |= VFIO_IOMMU_SPAPR_TCE_FLAG_DDW;

I think you want to set this flag regardless of whether the user has
provided space for it.  A valid use model is to call with the minimum
size and look at the flags to determine if it needs to be called again
with a larger size.

> +
> +				ret = data->ops->query(data,
> +						&info.current_windows,
> +						&info.windows_available,
> +						&info.page_size_mask);
> +				if (ret)
> +					return ret;
> +			} else {
> +				info.current_windows = 0;
> +				info.windows_available = 0;
> +				info.page_size_mask = 0;
> +			}
> +			minsz = ddwsz;

It's not really any longer the min size, is it?

> +		}
> +
>  		if (copy_to_user((void __user *)arg, &info, minsz))
>  			return -EFAULT;
>  
> @@ -412,12 +441,106 @@ static long tce_iommu_ioctl(void *iommu_data,
>  		tce_iommu_disable(container);
>  		mutex_unlock(&container->lock);
>  		return 0;
> +
>  	case VFIO_EEH_PE_OP:
>  		if (!container->grp)
>  			return -ENODEV;
>  
>  		return vfio_spapr_iommu_eeh_ioctl(container->grp,
>  						  cmd, arg);
> +
> +	case VFIO_IOMMU_SPAPR_TCE_CREATE: {
> +		struct vfio_iommu_spapr_tce_create create;
> +		struct spapr_tce_iommu_group *data;
> +		struct iommu_table *tbl;
> +
> +		if (WARN_ON(!container->grp))

redux previous comment on this warning

> +			return -ENXIO;
> +
> +		data = iommu_group_get_iommudata(container->grp);
> +
> +		minsz = offsetofend(struct vfio_iommu_spapr_tce_create,
> +				start_addr);
> +
> +		if (copy_from_user(&create, (void __user *)arg, minsz))
> +			return -EFAULT;
> +
> +		if (create.argsz < minsz)
> +			return -EINVAL;
> +
> +		if (create.flags)
> +			return -EINVAL;
> +
> +		if (!data->ops->create || !data->iommu_owner)
> +			return -ENOSYS;
> +
> +		BUG_ON(!data || !data->ops || !data->ops->remove);

Little late for this test since we'll oops on the previous test.  Why is
this a BUG_ON?  A user could exploit this on a system with only a
partial set of callbacks.

> +
> +		ret = data->ops->create(data, create.page_shift,
> +				create.window_shift, &tbl);
> +		if (ret)
> +			return ret;
> +
> +		ret = try_increment_locked_vm(tbl);
> +		if (ret) {
> +			data->ops->remove(data, tbl);
> +			return ret;
> +		}
> +
> +		create.start_addr = tbl->it_offset << tbl->it_page_shift;
> +
> +		if (copy_to_user((void __user *)arg, &create, minsz)) {
> +			data->ops->remove(data, tbl);
> +			decrement_locked_vm(tbl);
> +			return -EFAULT;
> +		}
> +		mutex_lock(&container->lock);
> +		++container->windows_num;
> +		mutex_unlock(&container->lock);
> +
> +		return ret;
> +	}
> +	case VFIO_IOMMU_SPAPR_TCE_REMOVE: {
> +		struct vfio_iommu_spapr_tce_remove remove;
> +		struct spapr_tce_iommu_group *data;
> +		struct iommu_table *tbl;
> +
> +		if (WARN_ON(!container->grp))
> +			return -ENXIO;
> +
> +		data = iommu_group_get_iommudata(container->grp);
> +
> +		minsz = offsetofend(struct vfio_iommu_spapr_tce_remove,
> +				start_addr);
> +
> +		if (copy_from_user(&remove, (void __user *)arg, minsz))
> +			return -EFAULT;
> +
> +		if (remove.argsz < minsz)
> +			return -EINVAL;
> +
> +		if (remove.flags)
> +			return -EINVAL;
> +
> +		if (!data->ops->remove || !data->iommu_owner)

On this one we don't both to get data/data->ops.  Is there also an
exploit where the user can call these CREATE/REMOVE interfaces even
though INFO doesn't expose them if only a partial set of callbacks are
present?

> +			return -ENOSYS;
> +
> +		tbl = spapr_tce_find_table(container, data, remove.start_addr);

What happens if this returns the 0 index rather than the expected 1
index table?  Why doesn't this call ops->find_table()?

> +		if (!tbl)
> +			return -EINVAL;
> +
> +		ret = data->ops->remove(data, tbl);
> +		if (ret)
> +			return ret;
> +
> +		decrement_locked_vm(tbl);
> +
> +		mutex_lock(&container->lock);
> +		--container->windows_num;
> +		mutex_unlock(&container->lock);
> +
> +		return 0;
> +	}
>  	}
>  
>  	return -ENOTTY;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 6612974..e71a6ef 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -451,9 +451,13 @@ struct vfio_iommu_type1_dma_unmap {
>   */
>  struct vfio_iommu_spapr_tce_info {
>  	__u32 argsz;
> -	__u32 flags;			/* reserved for future use */
> +	__u32 flags;
> +#define VFIO_IOMMU_SPAPR_TCE_FLAG_DDW	1 /* Support dynamic windows */
>  	__u32 dma32_window_start;	/* 32 bit window start (bytes) */
>  	__u32 dma32_window_size;	/* 32 bit window size (bytes) */
> +	__u32 current_windows;
> +	__u32 windows_available;
> +	__u32 page_size_mask;
>  };
>  
>  #define VFIO_IOMMU_SPAPR_TCE_GET_INFO	_IO(VFIO_TYPE, VFIO_BASE + 12)
> @@ -489,6 +493,25 @@ struct vfio_eeh_pe_op {
>  
>  #define VFIO_EEH_PE_OP			_IO(VFIO_TYPE, VFIO_BASE + 21)
>  
> +struct vfio_iommu_spapr_tce_create {
> +	__u32 argsz;
> +	__u32 flags;
> +	/* in */
> +	__u32 page_shift;
> +	__u32 window_shift;
> +	/* out */
> +	__u64 start_addr;
> +};
> +#define VFIO_IOMMU_SPAPR_TCE_CREATE	_IO(VFIO_TYPE, VFIO_BASE + 18)
> +
> +struct vfio_iommu_spapr_tce_remove {
> +	__u32 argsz;
> +	__u32 flags;
> +	/* in */
> +	__u64 start_addr;
> +};
> +#define VFIO_IOMMU_SPAPR_TCE_REMOVE	_IO(VFIO_TYPE, VFIO_BASE + 19)
> +

Zero comments, no good.

>  /* ***************************************************************** */
>  
>  #endif /* _UAPIVFIO_H */



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