From: Michael Kelley <mhklinux@outlook.com> mainline inclusion from mainline-v6.10-rc1 commit 2650073f1b5858008c32712f3d9e1e808ce7e967 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBET92 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- iommu_dma_map_page() allocates swiotlb memory as a bounce buffer when an untrusted device wants to map only part of the memory in an granule. The goal is to disallow the untrusted device having DMA access to unrelated kernel data that may be sharing the granule. To meet this goal, the bounce buffer itself is zeroed, and any additional swiotlb memory up to alloc_size after the bounce buffer end (i.e., "post-padding") is also zeroed. However, as of commit 901c7280ca0d ("Reinstate some of "swiotlb: rework "fix info leak with DMA_FROM_DEVICE"""), swiotlb_tbl_map_single() always initializes the contents of the bounce buffer to the original memory. Zeroing the bounce buffer is redundant and probably wrong per the discussion in that commit. Only the post-padding needs to be zeroed. Also, when the DMA min_align_mask is non-zero, the allocated bounce buffer space may not start on a granule boundary. The swiotlb memory from the granule boundary to the start of the allocated bounce buffer might belong to some unrelated bounce buffer. So as described in the "second issue" in [1], it can't be zeroed to protect against untrusted devices. But as of commit af133562d5af ("swiotlb: extend buffer pre-padding to alloc_align_mask if necessary"), swiotlb_tbl_map_single() allocates pre-padding slots when necessary to meet min_align_mask requirements, making it possible to zero the pre-padding area as well. Finally, iommu_dma_map_page() uses the swiotlb for untrusted devices and also for certain kmalloc() memory. Current code does the zeroing for both cases, but it is needed only for the untrusted device case. Fix all of this by updating iommu_dma_map_page() to zero both the pre-padding and post-padding areas, but not the actual bounce buffer. Do this only in the case where the bounce buffer is used because of an untrusted device. [1] https://lore.kernel.org/all/20210929023300.335969-1-stevensd@google.com/ Signed-off-by: Michael Kelley <mhklinux@outlook.com> Reviewed-by: Petr Tesarik <petr@tesarici.cz> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Kaixiong Yu <yukaixiong@huawei.com> --- drivers/iommu/dma-iommu.c | 29 ++++++++++++++++------------- include/linux/iova.h | 5 +++++ 2 files changed, 21 insertions(+), 13 deletions(-) diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c index 8ec46517cc37..b8258a474edf 100644 --- a/drivers/iommu/dma-iommu.c +++ b/drivers/iommu/dma-iommu.c @@ -1193,9 +1193,6 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page, */ if (dev_use_swiotlb(dev, size, dir) && iova_offset(iovad, phys | size)) { - void *padding_start; - size_t padding_size, aligned_size; - if (!is_swiotlb_active(dev)) { dev_warn_once(dev, "DMA bounce buffers are inactive, unable to map unaligned transaction.\n"); return DMA_MAPPING_ERROR; @@ -1203,24 +1200,30 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page, trace_swiotlb_bounced(dev, phys, size); - aligned_size = iova_align(iovad, size); phys = swiotlb_tbl_map_single(dev, phys, size, iova_mask(iovad), dir, attrs); if (phys == DMA_MAPPING_ERROR) return DMA_MAPPING_ERROR; - /* Cleanup the padding area. */ - padding_start = phys_to_virt(phys); - padding_size = aligned_size; + /* + * Untrusted devices should not see padding areas with random + * leftover kernel data, so zero the pre- and post-padding. + * swiotlb_tbl_map_single() has initialized the bounce buffer + * proper to the contents of the original memory buffer. + */ + if (dev_is_untrusted(dev)) { + size_t start, virt = (size_t)phys_to_virt(phys); - if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) && - (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)) { - padding_start += size; - padding_size -= size; - } + /* Pre-padding */ + start = iova_align_down(iovad, virt); + memset((void *)start, 0, virt - start); - memset(padding_start, 0, padding_size); + /* Post-padding */ + start = virt + size; + memset((void *)start, 0, + iova_align(iovad, start) - start); + } } if (!coherent && !(attrs & DMA_ATTR_SKIP_CPU_SYNC)) diff --git a/include/linux/iova.h b/include/linux/iova.h index 83c00fac2acb..d2c4fd923efa 100644 --- a/include/linux/iova.h +++ b/include/linux/iova.h @@ -65,6 +65,11 @@ static inline size_t iova_align(struct iova_domain *iovad, size_t size) return ALIGN(size, iovad->granule); } +static inline size_t iova_align_down(struct iova_domain *iovad, size_t size) +{ + return ALIGN_DOWN(size, iovad->granule); +} + static inline dma_addr_t iova_dma_addr(struct iova_domain *iovad, struct iova *iova) { return (dma_addr_t)iova->pfn_lo << iova_shift(iovad); -- 2.34.1