3.2.54-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Andy Honig <ahonig@xxxxxxxxxx> commit b963a22e6d1a266a67e9eecc88134713fd54775c upstream. Under guest controllable circumstances apic_get_tmcct will execute a divide by zero and cause a crash. If the guest cpuid support tsc deadline timers and performs the following sequence of requests the host will crash. - Set the mode to periodic - Set the TMICT to 0 - Set the mode bits to 11 (neither periodic, nor one shot, nor tsc deadline) - Set the TMICT to non-zero. Then the lapic_timer.period will be 0, but the TMICT will not be. If the guest then reads from the TMCCT then the host will perform a divide by 0. This patch ensures that if the lapic_timer.period is 0, then the division does not occur. Reported-by: Andrew Honig <ahonig@xxxxxxxxxx> Signed-off-by: Andrew Honig <ahonig@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> [bwh: Backported to 3.2: s/kvm_apic_get_reg/apic_get_reg/] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- arch/x86/kvm/lapic.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -537,7 +537,8 @@ static u32 apic_get_tmcct(struct kvm_lap ASSERT(apic != NULL); /* if initial count is 0, current count should also be 0 */ - if (apic_get_reg(apic, APIC_TMICT) == 0) + if (apic_get_reg(apic, APIC_TMICT) == 0 || + apic->lapic_timer.period == 0) return 0; remaining = hrtimer_get_remaining(&apic->lapic_timer.timer); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html