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....@intel.com>
> Cc: Jacob Pan <jacob.jun....@linux.intel.com>
> Cc: Kevin Tian <kevin.t...@intel.com>
> Cc: Alan Cox <a...@linux.intel.com>
> Cc: Mika Westerberg <mika.westerb...@intel.com>
> Signed-off-by: Lu Baolu <baolu...@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).
> + 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?
> + 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 {};
>
--
Yours sincerely,
Pavel Begunkov
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