CVE-2026-46148: spi: microchip-core-qspi: control built-in cs manually
In the Linux kernel, the following vulnerability has been resolved:
spi: microchip-core-qspi: control built-in cs manually
The coreQSPI IP supports only a single chip select, which is automagically operated by the hardware - set low when the transmit buffer first gets written to and set high when the number of bytes written to the TOTALBYTES field of the FRAMES register have been sent on the bus. Additional devices must use GPIOs for their chip selects. It was reported to me that if there are two devices attached to this QSPI controller that the in-built chip select is set low while linux tries to access the device attached to the GPIO.
This went undetected as the boards that connected multiple devices to the SPI controller all exclusively used GPIOs for chip selects, not relying on the built-in chip select at all. It turns out that this was because the built-in chip select, when controlled automagically, is set low when active and high when inactive, thereby ruling out its use for active-high devices or devices that need to transmit with the chip select disabled.
Modify the driver so that it controls chip select directly, retaining the behaviour for memops of setting the chip select active for the entire duration of the transfer in the execop callback. For regular transfers, implement the setcs callback for the core to use.
As part of this, the existing setup callback, mchpcoreqspisetupop(), is removed. Modifying the CLKIDLE field is not safe to do during operation when there are multiple devices, so this code is removed entirely. Setting the MASTER and ENABLE fields is something that can be done once at probe, it doesn't need to be re-run for each device. Instead the new setup callback sets the built-in chip select to its inactive state for active-low devices, as the reset value of the chip select in software controlled mode is low.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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Implement the set_cs callback so the driver controls chip select directly for regular transfers; keep the built-in chip select inactive for active-low devices.
Linux kernel Microchip CoreQSPI driver chip-select control for regular SPI transfers = set_cs callback - Configuration
Configure additional devices attached to the SPI controller to use GPIOs for their chip selects rather than relying on the built-in chip select.
Microchip CoreQSPI controller chip-selects for additional devices = GPIOs
Event History
Frequently Asked Questions
Which deployments are realistically exposed?
The reported condition involves a coreQSPI controller with two attached devices, where one uses the controller’s built-in chip select and another uses a GPIO chip select. Accessing the GPIO-selected device can cause the built-in chip select to be driven low.
Are systems that use only GPIO chip selects affected by the reported behavior?
The issue went undetected on boards that connected multiple SPI devices but used GPIOs exclusively for all chip selects. The described problematic configuration depends on use of the built-in chip select alongside a GPIO-selected device.
What level of access is indicated for exploitation?
The CVSS vector indicates local access, low attack complexity, low privileges required, and no user interaction. The stated impact is availability only, with no confidentiality or integrity impact.