CVE-2021-47047 in Linux
Summary
by MITRE • 02/28/2024
In the Linux kernel, the following vulnerability has been resolved:
spi: spi-zynqmp-gqspi: return -ENOMEM if dma_map_single fails
The spi controller supports 44-bit address space on AXI in DMA mode, so set dma_addr_t width to 44-bit to avoid using a swiotlb mapping. In addition, if dma_map_single fails, it should return immediately instead of continuing doing the DMA operation which bases on invalid address.
This fixes the following crash which occurs in reading a big block from flash:
[ 123.633577] zynqmp-qspi ff0f0000.spi: swiotlb buffer is full (sz: 4194304 bytes), total 32768 (slots), used 0 (slots)
[ 123.644230] zynqmp-qspi ff0f0000.spi: ERR:rxdma:memory not mapped
[ 123.784625] Unable to handle kernel paging request at virtual address 00000000003fffc0
[ 123.792536] Mem abort info:
[ 123.795313] ESR = 0x96000145
[ 123.798351] EC = 0x25: DABT (current EL), IL = 32 bits
[ 123.803655] SET = 0, FnV = 0
[ 123.806693] EA = 0, S1PTW = 0
[ 123.809818] Data abort info:
[ 123.812683] ISV = 0, ISS = 0x00000145
[ 123.816503] CM = 1, WnR = 1
[ 123.819455] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000805047000
[ 123.825887] [00000000003fffc0] pgd=0000000803b45003, p4d=0000000803b45003, pud=0000000000000000
[ 123.834586] Internal error: Oops: 96000145 [#1] PREEMPT SMP
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Analysis
by VulDB Data Team • 08/17/2025
The vulnerability described in CVE-2021-47047 affects the Linux kernel's spi-zynqmp-gqspi driver, which manages the Quad SPI controller on Xilinx Zynq UltraScale+ MPSoC platforms. This flaw represents a critical memory management issue that can lead to system crashes and potential denial of service conditions. The vulnerability specifically addresses improper error handling in DMA memory mapping operations within the SPI controller driver, creating a scenario where invalid memory addresses are processed during flash read operations.
The technical root cause lies in the driver's failure to properly validate DMA mapping results before proceeding with data transfer operations. When dma_map_single() function fails to map memory addresses, the driver continues execution instead of immediately returning an error code. This results in attempting DMA operations using invalid memory addresses, which subsequently triggers kernel page faults and system crashes. The driver's inability to handle the -ENOMEM return code from DMA mapping functions creates a path where memory corruption occurs, particularly when reading large data blocks from flash storage devices.
This vulnerability directly impacts systems utilizing Xilinx Zynq UltraScale+ MPSoC platforms with SPI flash interfaces, including embedded systems, industrial control devices, and network equipment that depend on this specific hardware configuration. The crash manifestation occurs during large block reads from flash memory, where the system's software I/O buffer (swiotlb) becomes exhausted, leading to a complete system hang. The error logs show the swiotlb buffer filling up with 4194304 bytes of requested memory, indicating a significant memory allocation failure that cascades into a kernel memory management fault.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise system availability and data integrity in embedded environments. Systems relying on SPI flash storage for boot processes, firmware updates, or critical data storage become vulnerable to unexpected shutdowns that could result in corrupted boot sequences or data loss. The vulnerability aligns with CWE-252, which describes "Unchecked Return Value" in security contexts, and maps to ATT&CK technique T1499.001 for "Fragging" where system resources are exhausted to cause denial of service conditions.
Mitigation strategies should focus on implementing proper error handling for DMA operations and ensuring that all memory mapping functions are validated before proceeding with data transfer operations. The fix involves modifying the driver to immediately return -ENOMEM when dma_map_single() fails, preventing further execution with invalid memory addresses. System administrators should prioritize kernel updates that include this specific patch, particularly in embedded environments where system availability is critical. Additionally, monitoring for swiotlb buffer exhaustion warnings can help identify systems approaching this vulnerability threshold, allowing for proactive mitigation measures. The solution also requires ensuring that DMA address space configurations properly account for the 44-bit address requirements of the AXI interface, preventing unnecessary fallback to software I/O buffer mechanisms that can lead to resource exhaustion.