CVE-2026-64149: dma-mapping: move dma_map_resource() sanity check into debug code

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

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

dma-mapping: move dma_map_resource() sanity check into debug code

dma_map_resource() uses pfn_valid() to ensure the range is not RAM.
However, pfn_valid() only checks for availability of the memory map for
a PFN but it does not ensure that the PFN is actually backed by RAM. On
ARM64 with SPARSEMEM (128MB section granularity), MMIO addresses that
share a section with RAM will falsely trigger the WARN_ON_ONCE and cause
dma_map_resource() to return DMA_MAPPING_ERROR.

This causes a WARNING on Raspberry Pi 4 during spi_bcm2835 probe because
the SPI FIFO register (0xfe204004) falls in the same sparsemem section
as the end of RAM (0xf8000000-0xfbffffff), both in section 31
(0xf8000000-0xffffffff).

Move the sanity check from dma_map_resource() into debug_dma_map_phys()
and replace the unreliable pfn_valid() with pfn_valid() &&
!PageReserved(), which correctly identifies actual usable RAM without
false positives for MMIO regions that happen to have struct pages.

Since dma_map_resource() is dma_map_phys(DMA_ATTR_MMIO), the check
applies equally to both APIs. Any non-reserved page represents kernel
memory to a sufficient degree that using DMA_ATTR_MMIO on it is almost
certainly wrong and risks breaking coherency on non-coherent platforms.
ZONE_DEVICE pages used for PCI P2P DMA (MEMORY_DEVICE_PCI_P2PDMA) have
PageReserved set, so they will not trigger a false positive.

The check no longer blocks the mapping and uses err_printk() to
integrate with dma-debug filtering.

The Linux kernel CVE team has assigned CVE-2026-64149 to this issue.


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

	Issue introduced in 6.18 with commit f7326196a781622b33bfbdabb00f5e72b5fb5679 and fixed in 6.18.34 with commit 181e67bc11c5ec5b87c6c512c2078752b23ca8d4
	Issue introduced in 6.18 with commit f7326196a781622b33bfbdabb00f5e72b5fb5679 and fixed in 7.0.11 with commit 004a777879ff629f6e0ca3d09ad09fa3452bcc4d
	Issue introduced in 6.18 with commit f7326196a781622b33bfbdabb00f5e72b5fb5679 and fixed in 7.1 with commit af0c3f05866237f7592219bfe05387bc3bfc99b5

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-2026-64149
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/debug.c
	kernel/dma/mapping.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/181e67bc11c5ec5b87c6c512c2078752b23ca8d4
	https://git.kernel.org/stable/c/004a777879ff629f6e0ca3d09ad09fa3452bcc4d
	https://git.kernel.org/stable/c/af0c3f05866237f7592219bfe05387bc3bfc99b5