CVE-2024-35814

In the Linux kernel, the following vulnerability has been resolved:
swiotlb: Fix double-allocation of slots due to broken alignment handling
Commit bbb73a103fbb (“swiotlb: fix a braino in the alignment check fix”),
which was a fix for commit 0eee5ae10256 (“swiotlb: fix slot alignment
checks”), causes a functional regression with vsock in a virtual machine
using bouncing via a restricted DMA SWIOTLB pool. When virtio allocates the
virtqueues for the vsock device using dma_alloc_coherent(), the SWIOTLB
search can return page-unaligned allocations if ‘area->index’ was left
unaligned by a previous allocation from the buffer: # Final address in
brackets is the SWIOTLB address returned to the caller | virtio-pci
0000:00:07.0: orig_addr 0x0 alloc_size 0x2000, iotlb_align_mask 0x800
stride 0x2: got slot 1645-1649/7168 (0x98326800) | virtio-pci 0000:00:07.0:
orig_addr 0x0 alloc_size 0x2000, iotlb_align_mask 0x800 stride 0x2: got
slot 1649-1653/7168 (0x98328800) | virtio-pci 0000:00:07.0: orig_addr 0x0
alloc_size 0x2000, iotlb_align_mask 0x800 stride 0x2: got slot
1653-1657/7168 (0x9832a800) This ends badly (typically buffer corruption
and/or a hang) because swiotlb_alloc() is expecting a page-aligned
allocation and so blindly returns a pointer to the ‘struct page’
corresponding to the allocation, therefore double-allocating the first half
(2KiB slot) of the 4KiB page. Fix the problem by treating the allocation
alignment separately to any additional alignment requirements from the
device, using the maximum of the two as the stride to search the buffer
slots and taking care to ensure a minimum of page-alignment for buffers
larger than a page. This also resolves swiotlb allocation failures occuring
due to the inclusion of ~PAGE_MASK in ‘iotlb_align_mask’ for large
allocations and resulting in alignment requirements exceeding
swiotlb_max_mapping_size().