Subject: CVE-2024-35814: swiotlb: Fix double-allocation of slots due to broken alignment handling

From: Greg Kroah-Hartman <[email-masked]>

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().

The Linux kernel CVE team has assigned CVE-2024-35814 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.3 with commit 0eee5ae10256 and fixed in 6.6.24 with commit 3e7acd6e25ba
	Issue introduced in 6.3 with commit 0eee5ae10256 and fixed in 6.7.12 with commit c88668aa6c1d
	Issue introduced in 6.3 with commit 0eee5ae10256 and fixed in 6.8.3 with commit 777391743771
	Issue introduced in 6.3 with commit 0eee5ae10256 and fixed in 6.9 with commit 04867a7a3332

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-35814
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	kernel/dma/swiotlb.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3e7acd6e25ba77dde48c3b721c54c89cd6a10534
	https://git.kernel.org/stable/c/c88668aa6c1da240ea3eb4d128b7906e740d3cb8
	https://git.kernel.org/stable/c/777391743771040e12cc40d3d0d178f70c616491
	https://git.kernel.org/stable/c/04867a7a33324c9c562ee7949dbcaab7aaad1fb4