CVE-2023-54167

Bug

On m68k systems where physical memory does not start at address zero (e.g. Amiga), booting with an initial RAM disk triggers a kernel crash because phys_to_virt() is invoked before paging_init(). The phys_to_virt() macro depends on m68k_memoffset and module_fixup(), which are only initialized during paging_init(). Calling it prematurely leads to an invalid virtual address and an Oops.

Exploitation

No special attacker interaction is required; the crash occurs during normal boot when an initrd is present on affected hardware. The prerequisite is a m68k platform with a non-zero physical memory base. Authentication or network access is not needed, as the bug manifests at boot time.

Impact

The kernel fails to boot with an "Unable to handle kernel access" panic, rendering the system unusable. An attacker capable of booting a crafted initrd could cause denial of service, but the primary risk is system instability for legitimate users.

Mitigation

The fix, committed in kernel stable branches, postpones the phys_to_virt() handling for the initial ramdisk until after paging_init() and reduces #ifdef clutter by using IS_ENABLED() [1][2]. Affected users should apply the latest stable kernel updates; no workaround is available without patching.