Messages in this thread Patch in this message | | | Subject | Re: [PATCH v2 04/13] KVM: x86: dynamic kvm_apic_map | From | Yang Zhang <> | Date | Mon, 11 Jul 2016 18:14:31 +0800 |
| |
On 2016/7/11 15:43, Paolo Bonzini wrote: > > > On 11/07/2016 08:07, Yang Zhang wrote: >>> >>> mutex_lock(&kvm->arch.apic_map_lock); >>> >>> + kvm_for_each_vcpu(i, vcpu, kvm) >>> + if (kvm_apic_present(vcpu)) >>> + max_id = max(max_id, kvm_apic_id(vcpu->arch.apic)); >>> + >>> + new = kzalloc(sizeof(struct kvm_apic_map) + >>> + sizeof(struct kvm_lapic *) * (max_id + 1), >>> GFP_KERNEL); >>> + >> >> I think this may cause the host runs out of memory if a malicious guest >> did follow thing: >> 1. vcpu a is doing apic map recalculation. >> 2. vcpu b write the apic id with 0xff >> 3. then vcpu b enable the x2apic: in kvm_lapic_set_base(), we will set >> apic_base to new value before reset the apic id. >> 4. vcpu a may see the x2apic enabled in vcpu b plus an old apic >> id(0xff), and max_id will become (0xff >> 24). > > The bug is not really here but in patch 6---but you're right nevertheless! > > I guess the easiest solution is to replace kvm_apic_id with a field in > struct kvm_lapic, which is already shifted right by 24 in xAPIC mode.
Or we can just simply put the assignment of apic_base to the end.
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index fdc05ae..9c69059 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1745,7 +1745,6 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value) return; }
- vcpu->arch.apic_base = value;
/* update jump label if enable bit changes */ if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE) { @@ -1753,7 +1752,6 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value) static_key_slow_dec_deferred(&apic_hw_disabled); else static_key_slow_inc(&apic_hw_disabled.key); - recalculate_apic_map(vcpu->kvm); }
if ((old_value ^ value) & X2APIC_ENABLE) { @@ -1764,6 +1762,8 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value) kvm_x86_ops->set_virtual_x2apic_mode(vcpu, false); }
+ vcpu->arch.apic_base = value; + recalculate_apic_map(vcpu->kvm); apic->base_address = apic->vcpu->arch.apic_base & MSR_IA32_APICBASE_BASE;
btw, i noticed that there is no apic map recalculation after turn off the x2apic mode.Is it correct?
-- best regards yang
| |