Return-Path: Message-Id: <20140512003206.309441586@1wt.eu> Date: Mon, 12 May 2014 02:34:15 +0200 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Andrew Honig , Paolo Bonzini , Willy Tarreau Subject: [ 135/143] KVM: x86: Fix potential divide by 0 in lapic (CVE-2013-6367) In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: 2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Andy Honig 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 Cc: stable@vger.kernel.org Signed-off-by: Andrew Honig Signed-off-by: Paolo Bonzini [dannf: backported to Debian's 2.6.32] Signed-off-by: Willy Tarreau --- 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 8dfeaaa..b77857f 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); -- 1.7.12.2.21.g234cd45.dirty