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Raspberry Pi 4 SPI Driver DMA Mapping Error
published 3 months ago
Summary
The Linux kernel's SPI driver on Raspberry Pi 4 may incorrectly trigger a warning when trying to access a specific memory address. This is due to a misinterpretation of memory availability. The issue has been resolved by improving the kernel's memory mapping checks, which should prevent this warning from occurring in the future. No action is required for most users, but kernel developers may need to update their code accordingly.
What to do
- Update linux kernel to version 7.0.11.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| Linux | linux | kernel |
>= 6.19.0, < 7.0.11 Fix: upgrade to 7.0.11
|
Original advisory text
dma-mapping: move dma_map_resource() sanity check into debug code
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.
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.
References
- https://git.kernel.org/stable/c/004a777879ff629f6e0ca3d09ad09fa3452bcc4d URL
- https://git.kernel.org/stable/c/181e67bc11c5ec5b87c6c512c2078752b23ca8d4 URL
- https://git.kernel.org/stable/c/af0c3f05866237f7592219bfe05387bc3bfc99b5 URL
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64149... Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-64149 Vendor Advisory
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git Product
Timeline
Published19 Jul 2026
Updated1 Aug 2026
First seen1 Aug 2026
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