The altivec_unavailable_exception function in arch/powerpc/kernel/traps.c in the Linux kernel before 2.6.19 on 64-bit systems mishandles the case where CONFIG_ALTIVEC is defined and the CPU actually supports Altivec, but the Altivec support was not detected by the kernel, which allows local users to cause a denial of service (panic) by triggering execution of an Altivec instruction.