Executive brief
A technical issue was identified in the Linux kernel's memory management system, specifically affecting how it handles hardware communication on certain devices like the Raspberry Pi 4. Under specific configurations, the system incorrectly flags legitimate hardware access as an error, which can prevent certain hardware components (like SPI controllers) from starting correctly. This primarily impacts system stability and the ability to use connected hardware peripherals, rather than posing a direct risk to data security.
Technical details
A vulnerability (or functional bug) was identified in the Linux kernel dma-mapping subsystem where dma_map_resource() incorrectly used pfn_valid() to validate that a memory range was not RAM. On ARM64 systems using SPARSEMEM with 128MB granularity, MMIO addresses residing in the same section as RAM would trigger a WARN_ON_ONCE and return DMA_MAPPING_ERROR. This caused driver probe failures, notably for the spi_bcm2835 on Raspberry Pi 4. The fix involves moving the sanity check to debug code and utilizing a more robust check (pfn_valid() && !PageReserved()) to distinguish between actual usable RAM and MMIO regions. This ensures that legitimate hardware resources are not blocked while still providing debug warnings for incorrect API usage that could risk memory coherency.
Affected products
- Linux Linux 6.18, 6.18.34, 7.0.11, 7.1
Timeline
- 2026-05-13: disclosed: Initial patch submission by Jianpeng Chang
- 2026-07-19: advisory: CVE-2026-64149 published