Re: [PATCH v4 4/9] iommu: Add bounce page APIs

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

Hi Pavel,

Thanks a lot for your reviewing.

On 6/11/19 8:10 PM, Pavel Begunkov wrote:
> 
> 
> On 03/06/2019 04:16, Lu Baolu wrote:
>> IOMMU hardware always use paging for DMA remapping.  The
>> minimum mapped window is a page size. The device drivers
>> may map buffers not filling whole IOMMU window. It allows
>> device to access to possibly unrelated memory and various
>> malicious devices can exploit this to perform DMA attack.
>>
>> This introduces the bouce buffer mechanism for DMA buffers
>> which doesn't fill a minimal IOMMU page. It could be used
>> by various vendor specific IOMMU drivers as long as the
>> DMA domain is managed by the generic IOMMU layer. Below
>> APIs are added:
>>
>> * iommu_bounce_map(dev, addr, paddr, size, dir, attrs)
>>    - Map a buffer start at DMA address @addr in bounce page
>>      manner. For buffer parts that doesn't cross a whole
>>      minimal IOMMU page, the bounce page policy is applied.
>>      A bounce page mapped by swiotlb will be used as the DMA
>>      target in the IOMMU page table. Otherwise, the physical
>>      address @paddr is mapped instead.
>>
>> * iommu_bounce_unmap(dev, addr, size, dir, attrs)
>>    - Unmap the buffer mapped with iommu_bounce_map(). The bounce
>>      page will be torn down after the bounced data get synced.
>>
>> * iommu_bounce_sync(dev, addr, size, dir, target)
>>    - Synce the bounced data in case the bounce mapped buffer is
>>      reused.
>>
>> The whole APIs are included within a kernel option IOMMU_BOUNCE_PAGE.
>> It's useful for cases where bounce page doesn't needed, for example,
>> embedded cases.
>>
>> Cc: Ashok Raj <ashok.raj@intel.com>
>> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
>> Cc: Kevin Tian <kevin.tian@intel.com>
>> Cc: Alan Cox <alan@linux.intel.com>
>> Cc: Mika Westerberg <mika.westerberg@intel.com>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   drivers/iommu/Kconfig |  14 +++++
>>   drivers/iommu/iommu.c | 119 ++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/iommu.h |  35 +++++++++++++
>>   3 files changed, 168 insertions(+)
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index 83664db5221d..d837ec3f359b 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -86,6 +86,20 @@ config IOMMU_DEFAULT_PASSTHROUGH
>>   
>>   	  If unsure, say N here.
>>   
>> +config IOMMU_BOUNCE_PAGE
>> +	bool "Use bounce page for untrusted devices"
>> +	depends on IOMMU_API
>> +	select SWIOTLB
>> +	help
>> +	  IOMMU hardware always use paging for DMA remapping. The minimum
>> +	  mapped window is a page size. The device drivers may map buffers
>> +	  not filling whole IOMMU window. This allows device to access to
>> +	  possibly unrelated memory and malicious device can exploit this
>> +	  to perform a DMA attack. Select this to use a bounce page for the
>> +	  buffer which doesn't fill a whole IOMU page.
>> +
>> +	  If unsure, say N here.
>> +
>>   config OF_IOMMU
>>          def_bool y
>>          depends on OF && IOMMU_API
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 2a906386bb8e..fa44f681a82b 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -2246,3 +2246,122 @@ int iommu_sva_get_pasid(struct iommu_sva *handle)
>>   	return ops->sva_get_pasid(handle);
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_sva_get_pasid);
>> +
>> +#ifdef CONFIG_IOMMU_BOUNCE_PAGE
>> +
>> +/*
>> + * Bounce buffer support for external devices:
>> + *
>> + * IOMMU hardware always use paging for DMA remapping. The minimum mapped
>> + * window is a page size. The device drivers may map buffers not filling
>> + * whole IOMMU window. This allows device to access to possibly unrelated
>> + * memory and malicious device can exploit this to perform a DMA attack.
>> + * Use bounce pages for the buffer which doesn't fill whole IOMMU pages.
>> + */
>> +
>> +static inline size_t
>> +get_aligned_size(struct iommu_domain *domain, dma_addr_t addr, size_t size)
>> +{
>> +	unsigned long page_size = 1 << __ffs(domain->pgsize_bitmap);
>> +	unsigned long offset = page_size - 1;
>> +
>> +	return ALIGN((addr & offset) + size, page_size);
>> +}
>> +
>> +dma_addr_t iommu_bounce_map(struct device *dev, dma_addr_t iova,
>> +			    phys_addr_t paddr, size_t size,
>> +			    enum dma_data_direction dir,
>> +			    unsigned long attrs)
>> +{
>> +	struct iommu_domain *domain;
>> +	unsigned int min_pagesz;
>> +	phys_addr_t tlb_addr;
>> +	size_t aligned_size;
>> +	int prot = 0;
>> +	int ret;
>> +
>> +	domain = iommu_get_dma_domain(dev);
>> +	if (!domain)
>> +		return DMA_MAPPING_ERROR;
>> +
>> +	if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
>> +		prot |= IOMMU_READ;
>> +	if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)
>> +		prot |= IOMMU_WRITE;
>> +
>> +	aligned_size = get_aligned_size(domain, paddr, size);
>> +	min_pagesz = 1 << __ffs(domain->pgsize_bitmap);
>> +
>> +	/*
>> +	 * If both the physical buffer start address and size are
>> +	 * page aligned, we don't need to use a bounce page.
>> +	 */
>> +	if (!IS_ALIGNED(paddr | size, min_pagesz)) {
>> +		tlb_addr = swiotlb_tbl_map_single(dev,
>> +				__phys_to_dma(dev, io_tlb_start),
>> +				paddr, size, aligned_size, dir, attrs);
>> +		if (tlb_addr == DMA_MAPPING_ERROR)
>> +			return DMA_MAPPING_ERROR;
>> +	} else {
>> +		tlb_addr = paddr;
>> +	}
>> +
>> +	ret = iommu_map(domain, iova, tlb_addr, aligned_size, prot);
>> +	if (ret) {
>> +		swiotlb_tbl_unmap_single(dev, tlb_addr, size,
>> +					 aligned_size, dir, attrs);
> You would probably want to check, whether @tlb_addr came from
> swiotlb_tbl_map_single. (is_swiotlb_buffer() or reuse predicate above).

Right. Good catch.

> 
> 
>> +		return DMA_MAPPING_ERROR;
>> +	}
>> +
>> +	return iova;
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_bounce_map);
>> +
>> +static inline phys_addr_t
>> +iova_to_tlb_addr(struct iommu_domain *domain, dma_addr_t addr)
>> +{
>> +	if (unlikely(!domain->ops || !domain->ops->iova_to_phys))
>> +		return 0;
>> +
>> +	return domain->ops->iova_to_phys(domain, addr);
>> +}
>> +
>> +void iommu_bounce_unmap(struct device *dev, dma_addr_t iova, size_t size,
>> +			enum dma_data_direction dir, unsigned long attrs)
>> +{
>> +	struct iommu_domain *domain;
>> +	phys_addr_t tlb_addr;
>> +	size_t aligned_size;
>> +
>> +	domain = iommu_get_dma_domain(dev);
>> +	if (WARN_ON(!domain))
>> +		return;
>> +
>> +	aligned_size = get_aligned_size(domain, iova, size);
>> +	tlb_addr = iova_to_tlb_addr(domain, iova);
>> +	if (WARN_ON(!tlb_addr))
>> +		return;
>> +
>> +	iommu_unmap(domain, iova, aligned_size);
>> +	if (is_swiotlb_buffer(tlb_addr))
> 
> Is there any chance, this @tlb_addr is a swiotlb buffer, but owned by an
> API user? I mean something like
> iommu_bounce_map(swiotlb_tbl_map_single()).
> 
> Then, to retain ownership semantic, we shouldn't unmap it. Maybe to
> check and fail iommu_bounce_map() to be sure?

For untrusted devices, we always force iommu to enforce the DMA
isolation. There are no cases where @tlb_addr is a swiotlb buffer
owned by a device driver as far as I can see.

Best regards,
Baolu

> 
> 
>> +		swiotlb_tbl_unmap_single(dev, tlb_addr, size,
>> +					 aligned_size, dir, attrs);
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_bounce_unmap);
>> +
>> +void iommu_bounce_sync(struct device *dev, dma_addr_t addr, size_t size,
>> +		       enum dma_data_direction dir, enum dma_sync_target target)
>> +{
>> +	struct iommu_domain *domain;
>> +	phys_addr_t tlb_addr;
>> +
>> +	domain = iommu_get_dma_domain(dev);
>> +	if (WARN_ON(!domain))
>> +		return;
>> +
>> +	tlb_addr = iova_to_tlb_addr(domain, addr);
>> +	if (is_swiotlb_buffer(tlb_addr))
>> +		swiotlb_tbl_sync_single(dev, tlb_addr, size, dir, target);
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_bounce_sync);
>> +#endif /* CONFIG_IOMMU_BOUNCE_PAGE */
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 91af22a344e2..814c0da64692 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -25,6 +25,8 @@
>>   #include <linux/errno.h>
>>   #include <linux/err.h>
>>   #include <linux/of.h>
>> +#include <linux/swiotlb.h>
>> +#include <linux/dma-direct.h>
>>   
>>   #define IOMMU_READ	(1 << 0)
>>   #define IOMMU_WRITE	(1 << 1)
>> @@ -499,6 +501,39 @@ int iommu_sva_set_ops(struct iommu_sva *handle,
>>   		      const struct iommu_sva_ops *ops);
>>   int iommu_sva_get_pasid(struct iommu_sva *handle);
>>   
>> +#ifdef CONFIG_IOMMU_BOUNCE_PAGE
>> +dma_addr_t iommu_bounce_map(struct device *dev, dma_addr_t iova,
>> +			    phys_addr_t paddr, size_t size,
>> +			    enum dma_data_direction dir,
>> +			    unsigned long attrs);
>> +void iommu_bounce_unmap(struct device *dev, dma_addr_t iova, size_t size,
>> +			enum dma_data_direction dir, unsigned long attrs);
>> +void iommu_bounce_sync(struct device *dev, dma_addr_t addr, size_t size,
>> +		       enum dma_data_direction dir,
>> +		       enum dma_sync_target target);
>> +#else
>> +static inline
>> +dma_addr_t iommu_bounce_map(struct device *dev, dma_addr_t iova,
>> +			    phys_addr_t paddr, size_t size,
>> +			    enum dma_data_direction dir,
>> +			    unsigned long attrs)
>> +{
>> +	return DMA_MAPPING_ERROR;
>> +}
>> +
>> +static inline
>> +void iommu_bounce_unmap(struct device *dev, dma_addr_t iova, size_t size,
>> +			enum dma_data_direction dir, unsigned long attrs)
>> +{
>> +}
>> +
>> +static inline
>> +void iommu_bounce_sync(struct device *dev, dma_addr_t addr, size_t size,
>> +		       enum dma_data_direction dir, enum dma_sync_target target)
>> +{
>> +}
>> +#endif /* CONFIG_IOMMU_BOUNCE_PAGE */
>> +
>>   #else /* CONFIG_IOMMU_API */
>>   
>>   struct iommu_ops {};
>>
> 
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