CVE-2023-54278

Vulnerability

CVE-2023-54278 is a vulnerability in the Linux kernel affecting the s390 architecture. The root cause is that when debug pagealloc is enabled (either via CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc kernel command line option), the kernel uses large memory mappings on machines with EDAT1/EDAT2 support. This leads to a crash early during boot because the __kernel_map_pages function expects 4k pages but encounters larger mappings [1].

Exploitation

The vulnerability is triggered during the boot process, specifically in the __kernel_map_pages function called from __free_pages_ok and free_low_memory_core_early. The crash occurs as a kernel panic with an addressing exception. No special attacker access is required; the bug manifests automatically when the kernel is configured with debug pagealloc enabled on s390 systems with EDAT1/EDAT2. The attack surface is limited to local system boot, but it prevents the system from starting, resulting in a denial of service [1].

Impact

An attacker with the ability to enable debug pagealloc (e.g., via kernel command line or config) can cause a denial of service by preventing the system from booting. The impact is a system crash early in the boot process, making the system unusable. There is no indication of data corruption or privilege escalation; the primary consequence is a denial of service [1].

Mitigation

The fix, introduced in commit 601e467e29a9, adds code to split large mappings into 4k pages when debug pagealloc is enabled. This ensures compatibility with the page-level tracking required by debug pagealloc. The patch is included in stable kernel updates. Users should apply the latest kernel updates from their distribution. No workaround is mentioned other than disabling debug pagealloc if the fix cannot be applied [1].