CVE ID:	CVE-2024-35814
Description:	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().
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2024-35814 https://git.kernel.org/stable/c/04867a7a33324c9c562ee7949dbcaab7aaad1fb4 https://git.kernel.org/stable/c/04867a7a33324c9c562ee7949dbcaab7aaad1fb4 https://git.kernel.org/stable/c/3e7acd6e25ba77dde48c3b721c54c89cd6a10534 https://git.kernel.org/stable/c/3e7acd6e25ba77dde48c3b721c54c89cd6a10534 https://git.kernel.org/stable/c/777391743771040e12cc40d3d0d178f70c616491 https://git.kernel.org/stable/c/777391743771040e12cc40d3d0d178f70c616491 https://git.kernel.org/stable/c/c88668aa6c1da240ea3eb4d128b7906e740d3cb8 https://git.kernel.org/stable/c/c88668aa6c1da240ea3eb4d128b7906e740d3cb8