riscv: errata: select RISCV_ALTERNATIVE_EARLY for THEAD GHOSTWRITE

Overview

In the Linux kernel, the following vulnerability has been resolved:

riscv: errata: select RISCV_ALTERNATIVE_EARLY for THEAD GHOSTWRITE

errata_probe_ghostwrite() only marks the CPU as vulnerable when it is called at the RISCV_ALTERNATIVES_EARLY_BOOT stage, and the mitigation in ghostwrite_enable_mitigation() only takes effect if the vulnerable state was recorded before the boot alternatives are patched.

The early boot stage is only executed when CONFIG_RISCV_ALTERNATIVE_EARLY is enabled, which currently is only selected by ERRATA_THEAD_MAE. In a kernel built with ERRATA_THEAD_GHOSTWRITE=y but ERRATA_THEAD_MAE=n, the early alternatives never run, so ghostwrite_state is never set to VULNERABLE: ghostwrite_enable_mitigation() returns false, xtheadvector remains enabled, and sysfs reports "Not affected" on a vulnerable T-Head C9xx CPU.

Select RISCV_ALTERNATIVE_EARLY from ERRATA_THEAD_GHOSTWRITE so that the vulnerability is detected in the early boot stage and the default mitigation is applied.

Affected

• Linux >= 4bf97069239bcfca9840936313c7ac35a6e04488 < fa465a7819ecbe5801b78c088d3cadaf2664b8ca
• Linux >= 4bf97069239bcfca9840936313c7ac35a6e04488 < 7fee577a2fa78b9a76da015beec1ccf978746ebb
• Linux >= 4bf97069239bcfca9840936313c7ac35a6e04488 < 298510bbc7c3017c0faf481c6ea66f1065b657b4
• Linux 6.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.