Linux Kernel KASAN Vulnerability in Lazy MMU Mode on s390 Architecture

A vulnerability in the Linux kernel's memory management can lead to a crash on s390 architecture. When the kernel enters lazy MMU mode, a callback function can be invoked that allocates memory pages. If this function attempts to allocate a page while preemption is disabled, it can cause a deadlock, leading to a system crash. This issue arises because the kernel's Address Sanitizer (KASAN) feature tries to populate page tables in a way that can conflict with the scheduling of processes.

Impact

Exiting lazy MMU mode can cause a system crash, disrupting all processes and potentially leading to data loss.

Reproduction

The vulnerability can be reproduced by enabling the kernel's Address Sanitizer (KASAN) and then entering lazy MMU mode on an s390 system. Once in this state, the KASAN feature will attempt to allocate memory pages while preemption is disabled, causing the system to crash.

Remediation

Users can avoid this vulnerability by not enabling the Address Sanitizer (KASAN) feature while the kernel is in lazy MMU mode. Additionally, ensuring that preemption is not disabled during critical memory allocation processes can help prevent this issue.