CVE-2026-64149 in Linux
Summary
by MITRE • 07/19/2026
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.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability in question affects the Linux kernel's DMA mapping subsystem, specifically within the dma_map_resource() function implementation. This issue stems from an incorrect memory validation approach that utilizes pfn_valid() to determine whether a physical frame number represents actual RAM. The fundamental flaw lies in the assumption that pfn_valid() provides sufficient information to distinguish between real RAM and memory-mapped I/O regions, which proves inadequate in certain architectures like ARM64 with SPARSEMEM configuration where memory sections are mapped at 128MB granularity. When MMIO addresses share a section boundary with actual RAM, the function incorrectly flags these legitimate MMIO regions as problematic, triggering false warnings.
The technical execution of this vulnerability manifests during device probe operations, particularly affecting Raspberry Pi 4 systems when initializing the spi_bcm2835 driver. The specific memory address 0xfe204004 representing the SPI FIFO register coincides with section 31, which also contains the end of RAM at 0xf8000000-0xfbffffff. This architectural overlap causes pfn_valid() to return positive for MMIO addresses that should be treated as non-RAM resources, resulting in unnecessary WARNING messages and potential mapping failures. The problem demonstrates how sparse memory management can create false positives when relying solely on basic physical frame number validation without considering actual page residency characteristics.
The operational impact of this vulnerability extends beyond simple warning messages to potentially disrupt device initialization processes and create confusion during kernel debugging sessions. Systems utilizing ARM64 platforms with SPARSEMEM configurations become susceptible to these false positives, particularly affecting drivers that rely heavily on DMA mapping operations for hardware communication. The issue affects not only the specific Raspberry Pi 4 scenario but any system where MMIO regions share memory sections with RAM in SPARSEMEM architectures, creating a broader class of potential disruptions across similar embedded and server platforms.
The mitigation strategy implemented involves moving the sanity check from the primary dma_map_resource() function into the debug_dma_map_phys() implementation, which separates the validation logic from the critical execution path. This approach replaces the unreliable pfn_valid() function with a more robust combination of pfn_valid() && !PageReserved(), effectively distinguishing between actual RAM pages and MMIO regions that may have struct pages but are not reserved for kernel memory use. The solution addresses both dma_map_resource() and dma_map_phys() APIs since they share the same DMA_ATTR_MMIO attribute, ensuring comprehensive coverage of affected code paths. This change prevents false positives while maintaining the essential validation that protects against incorrect DMA mapping operations on kernel memory regions.
The fix aligns with established security practices by ensuring proper memory validation without compromising system functionality. It references core concepts from CWE categories related to improper validation of memory access and incorrect handling of memory reservations, while also supporting ATT&CK framework principles regarding system integrity maintenance and kernel-level privilege escalation prevention. The implementation uses err_printk() for integration with existing dma-debug filtering mechanisms, providing consistent logging behavior that allows administrators to properly monitor and filter these warnings according to their operational requirements. The solution specifically accounts for ZONE_DEVICE pages used in PCI P2P DMA operations by recognizing that these pages have PageReserved set, ensuring they don't trigger false positives while maintaining protection against actual kernel memory misuse scenarios.