In the Linux kernel, the following vulnerability has been resolved: arm64/fpsimd: signal: Forbid non-streaming SVE payload on SME-only systems When… (CVE-2026-98745)

The Linux kernel vulnerability (CVE-2026-98745) involves the arm64/fpsimd signal context restoration on systems supporting SME but not SVE. When system_supports_sme() returns true and system_supports_sve() returns false, restoring a specifically crafted SVE signal context can incorrectly assign non-streaming SVE state to a task. The kernel's restore_sve_fpsimd_context() function fails to reject cases where the SVE_SIG_FLAG_SM flag is clear but an SVE payload is present, leading to inconsistent task state. This can cause fatal EL1 undefined instruction exceptions when the kernel attempts to restore the task's ZCR_EL1 register. The fix involves reworking restore_sve_fpsimd_context() to reject these invalid cases, preventing the kernel from entering an unsupported state.

Exploitation of this vulnerability can cause kernel crashes due to fatal undefined instruction exceptions (EL1 UNDEF), resulting in system instability or denial of service on affected ARM64 systems configured with SME but without SVE support. There is no indication of privilege escalation or data corruption beyond system crashes.

A fix has been implemented in the Linux kernel to properly reject invalid SVE signal contexts on SME-only systems. Users should update to a kernel version that includes this fix. Since no vendor advisory or patch links are provided, check the official Linux kernel release notes or vendor advisories for the exact fixed versions and apply the update accordingly.