Linux Kernel FPSIMD State Clobbering Vulnerability on ARM64 Systems with SME

A vulnerability in the Linux kernel's handling of the Floating Point State for SIMD (FPSIMD) has been addressed. On ARM64 systems with Scalable Matrix Extension (SME), a thread's kernel FPSIMD state can be incorrectly overwritten during a context switch, just after the state has been restored. This issue arises when the CPU is in streaming Scalable Vector Extension (SVE) mode before switching to a thread that requires the kernel FPSIMD state. The restoration process can inadvertently disrupt the FPSIMD state, leading to a loss of critical data. Systems without SME are not affected.

Impact

The vulnerability can cause unintended modifications to the kernel FPSIMD state, potentially leading to incorrect program behavior or crashes.

Remediation

The vulnerability has been fixed by adjusting the order of operations in the context switching process. Users should ensure they are running a version of the Linux kernel that includes this fix.