diff options
authorAndy Honig <ahonig@google.com>2013-11-19 14:12:18 -0800
committerWilly Tarreau <w@1wt.eu>2014-05-19 07:54:34 +0200
commite3123670efb2e10e536fa7fe752d72a4ca5bce9a (patch)
parentba6e9bbbd6e3e28d92ff43981c2354307c095b7c (diff)
KVM: x86: Fix potential divide by 0 in lapic (CVE-2013-6367)
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> Cc: stable@vger.kernel.org Signed-off-by: Andrew Honig <ahonig@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> [dannf: backported to Debian's 2.6.32] Signed-off-by: Willy Tarreau <w@1wt.eu>
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 8dfeaaa70795..b77857fe037c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -519,7 +519,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
ASSERT(apic != NULL);
/* if initial count is 0, current count should also be 0 */
- if (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);