Linux Kernel CVE-2026-31628

This is a CPU microarchitectural side-channel vulnerability specific to AMD Zen1 silicon (Ryzen 1000/2000 series, EPYC Naples). The Zen1 hardware floating-point divider (FDIV unit) does not properly flush intermediate partial results between successive division operations executed by different hardware threads sharing a physical core. An attacker thread can time or sample these residual states to recover fragments of data processed by a victim thread's division instructions. The root cause class (CWE field is N/A per the submission) aligns conceptually with CWE-203 (Observable Discrepancy) or CWE-1342 (Information Exposure Through Microarchitectural State After Transient Execution), similar in nature to earlier MDS-class vulnerabilities (RIDL, Fallout, TAA). The fix employs a 'chicken bit' - a model-specific register (MSR) or control bit that disables the vulnerable hardware optimization pathway, trading minor performance for security. CPE data (cpe:2.3:a:linux:linux) covers all Linux versions from the initial commit (1da177e4c3f4) forward, with fixes landing as point releases across stable trees.