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charset="US-ASCII"; x-default=true When a device performs DMA to a bounce buffer, KMSAN is unaware of the write and does not mark the data as initialized. When swiotlb_bounce() later copies the bounce buffer back to the original buffer, memcpy propagates the uninitialized shadow to the original buffer, causing false positive uninit-value reports. Fix this by calling kmsan_unpoison_memory() on the bounce buffer before copying it back in the DMA_FROM_DEVICE path, so that memcpy naturally propagates initialized shadow to the destination. Suggested-by: Alexander Potapenko Link: https://lore.kernel.org/CAG_fn=WUGta-paG1BgsGRoAR+fmuCgh3xo=R3XdzOt_-DqSdHw@mail.gmail.com/ Fixes: 7ade4f10779c ("dma: kmsan: unpoison DMA mappings") Signed-off-by: Shigeru Yoshida --- kernel/dma/swiotlb.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index d8e6f1d889d5..9fd73700ddcf 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -30,6 +30,7 @@ #include #include #include +#include #include #include #include @@ -901,10 +902,19 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size local_irq_save(flags); page = pfn_to_page(pfn); - if (dir == DMA_TO_DEVICE) + if (dir == DMA_TO_DEVICE) { + /* + * Ideally, kmsan_check_highmem_page() + * could be used here to detect infoleaks, + * but callers may map uninitialized buffers + * that will be written by the device, + * causing false positives. + */ memcpy_from_page(vaddr, page, offset, sz); - else + } else { + kmsan_unpoison_memory(vaddr, sz); memcpy_to_page(page, offset, vaddr, sz); + } local_irq_restore(flags); size -= sz; @@ -913,8 +923,15 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size offset = 0; } } else if (dir == DMA_TO_DEVICE) { + /* + * Ideally, kmsan_check_memory() could be used here to detect + * infoleaks (uninitialized data being sent to device), but + * callers may map uninitialized buffers that will be written + * by the device, causing false positives. + */ memcpy(vaddr, phys_to_virt(orig_addr), size); } else { + kmsan_unpoison_memory(vaddr, size); memcpy(phys_to_virt(orig_addr), vaddr, size); } } -- 2.52.0