| From | Kamal Mostafa <> | Subject | [PATCH 3.8 052/166] KVM: x86: Fix potential divide by 0 in lapic (CVE-2013-6367) | Date | Wed, 15 Jan 2014 13:51:06 -0800 |
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3.8.13.16 -stable review patch. If anyone has any objections, please let me know.
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From: Andy Honig <ahonig@google.com>
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@google.com> Signed-off-by: Andrew Honig <ahonig@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- arch/x86/kvm/lapic.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index a2f492c..8d11f7735 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -807,7 +807,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic) ASSERT(apic != NULL); /* if initial count is 0, current count should also be 0 */ - if (kvm_apic_get_reg(apic, APIC_TMICT) == 0) + if (kvm_apic_get_reg(apic, APIC_TMICT) == 0 || + apic->lapic_timer.period == 0) return 0; remaining = hrtimer_get_remaining(&apic->lapic_timer.timer); -- 1.8.3.2
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