3.5.7.28 -stable review patch. If anyone has any objections, please let me
know.
------------------
From: Andy Honig <aho...@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 <aho...@google.com>
Signed-off-by: Andrew Honig <aho...@google.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
[ luis: backported to 3.5:
- use apic_get_reg() instead of kvm_apic_get_reg() ]
Signed-off-by: Luis Henriques <luis.henriq...@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 93c1574..399df2f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -545,7 +545,8 @@ 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);
--
1.8.3.2
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