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Since the fixed commits both zdev->iommu_bitmap and zdev->lazy_bitmap are allocated as vzalloc(zdev->iommu_pages / 8). The problem is that zdev->iommu_bitmap is a pointer to unsigned long but the above only yields an allocation that is a multiple of sizeof(unsigned long) which is 8 on s390x if the number of IOMMU pages is a multiple of 64. This in turn is the case only if the effective IOMMU aperture is a multiple of 64 * 4K = 256K. This is usually the case and so didn't cause visible issues since both the virt_to_phys(high_memory) reduced limit and hardware limits use nice numbers. Under KVM, and in particular with QEMU limiting the IOMMU aperture to the vfio DMA limit (default 65535), it is possible for the reported aperture not to be a multiple of 256K however. In this case we end up with an iommu_bitmap whose allocation is not a multiple of 8 causing bitmap operations to access it out of bounds. Sadly we can't just fix this in the obvious way and use bitmap_zalloc() because for large RAM systems (tested on 8 TiB) the zdev->iommu_bitmap grows too large for kmalloc(). So add our own bitmap_vzalloc() wrapper. This might be a candidate for common code, but this area of code will be replaced by the upcoming conversion to use the common code DMA API on s390 so just add a local routine. Fixes: |
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