CVE-2026-98143 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
accel: ethosu: Don't read the U65 rounding mode as a storage mode
Bits 15:14 of NPU_SET_{IFM,OFM}_PRECISION select the activation storage
mode on U85 only. On U65 the same field holds the rounding mode, and the command stream parser has read it as a storage mode since the driver was added.
That went unnoticed while unknown values fell through the switch, but now that they are rejected, every U65 command stream that asks for natural rounding (2) fails CMDSTREAM_BO_CREATE with -EINVAL. Mesa emits it for average pooling, concatenation, split, unpack, strided slice, LUT and argmax, which is 72 failures of the Teflon test suite on an i.MX93. Truncating rounding (1) is misread as well: it picks the two-tile address path and computes a bogus feature map size from tile bases the command stream never set.
Read the field as a storage mode only on the hardware where it is one.
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel driver for Arm Ethos-U neural processing units contains a critical logic error in how precision configuration commands are parsed, specifically affecting devices based on the U65 architecture while leaving earlier generations like the U85 unaffected. This vulnerability stems from an incorrect interpretation of bits 15 and 14 within the NPU_SET_IFM_PRECISION and NPU_SET_OFM_PRECISION command fields. In the original implementation, these bit positions were universally treated as selectors for activation storage modes across all hardware revisions. However, architectural differences between the U85 and U65 NPUs mean that on the newer U65 silicon, this specific field encodes rounding mode information rather than storage configuration. The driver failed to account for this divergence, leading to a fundamental misinterpretation of command stream instructions sent by user-space graphics libraries such as Mesa.
The operational impact of this flaw is severe and manifests primarily through immediate command rejection or silent data corruption depending on the specific precision value requested. When applications attempt to use natural rounding mode, represented by the integer value two in the configuration field, the driver incorrectly interprets it as an invalid storage mode selector. Consequently, the kernel rejects these commands with an EINVAL error code during CMDSTREAM_BO_CREATE operations. This results in a functional regression for common machine learning inference tasks including average pooling, concatenation, split operations, unpacking, strided slicing, look-up table processing, and argmax calculations. In testing environments such as the Teflon suite on i.MX93 hardware powered by Ethos-U65, this bug causes seventy-two distinct test failures, effectively breaking standard inference workflows that rely on these specific precision settings.
Beyond immediate command rejection, the vulnerability poses a risk of silent data corruption when truncating rounding mode is selected. The value one for truncating rounding is misinterpreted as a storage mode identifier, causing the driver to erroneously select a two-tile address path. This incorrect code path proceeds to compute feature map sizes using tile base addresses that were never properly initialized by the command stream parser. Such miscalculations can lead to out-of-bounds memory accesses or processing of garbage data, potentially compromising system stability and security if exploited in specific contexts where buffer boundaries are critical. The issue highlights a lack of hardware-specific validation logic within the driver's initialization sequence for precision parameters.
This vulnerability is best classified under CWE-20 Improper Input Validation as the software fails to correctly validate input based on the underlying hardware context, leading to incorrect processing paths. From an ATT&CK perspective, while this is primarily a functional defect rather than a direct exploitation vector, improper handling of command streams can be associated with TA0004 Privilege Escalation or TA0005 Defense Evasion if malicious actors could craft specific inputs to trigger the erroneous memory calculations and potentially access unauthorized kernel memory regions. The root cause lies in the absence of conditional logic that distinguishes between U85 and U65 hardware revisions when parsing precision configuration bits.
To mitigate this vulnerability, developers must update the Ethos-U driver to implement hardware-aware validation for precision settings. This involves detecting the specific NPU revision at runtime or compile time and applying the correct interpretation rules for bits 15 and 14 of the precision fields. For U65 devices, these bits should be processed as rounding mode selectors rather than storage modes. Additionally, robust error handling should ensure that invalid combinations are rejected early in the command stream parsing phase to prevent any potential memory corruption from uninitialized tile bases. Users relying on affected hardware should apply kernel updates containing this fix and verify that inference engines like Mesa are utilizing compatible precision configurations for their target deployment platforms.