Linux Kernel ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP Disabling Vulnerability on s390

A vulnerability has been identified in the Linux kernel on the s390 architecture, related to the handling of huge pages in memory management. The issue arises from enabling the 'ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP' configuration, which leads to crashes. This happens because the kernel modifies page tables without properly flushing the Translation Lookaside Buffer (TLB) entries. On s390, it is not permissible to directly replace a valid page table entry with another valid entry without first invalidating it, as this can cause random crashes or data corruption. The current implementation of the huge page optimization does not comply with these architectural requirements, prompting the need to disable this optimization.

Impact

The vulnerability can cause reproducible crashes and potential data corruption on systems running the affected Linux kernel version with the 'ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP' option enabled.

Reproduction

To reproduce this vulnerability, enable the 'ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP' option in the Linux kernel configuration for the s390 architecture. After compiling and running the kernel with this option, the system will experience crashes due to the improper handling of page table entries, demonstrating the vulnerability.

Remediation

Users can disable the 'ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP' option in the kernel configuration to address this vulnerability. After making this change, the kernel should be recompiled and the system rebooted to apply the update.