2018-08-30 10:03+0800, Wanpeng Li:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> Dan Carpenter reported that the untrusted data returns from kvm_register_read()
> results in the following static checker warning:
> arch/x86/kvm/lapic.c:576 kvm_pv_send_ipi()
> error: buffer underflow 'map->phys_map' 's32min-s32max'
>
> KVM guest can easily trigger this by executing the following assembly sequence
> in Ring0:
>
> mov $10, %rax
> mov $0xFFFFFFFF, %rbx
> mov $0xFFFFFFFF, %rdx
> mov $0, %rsi
> vmcall
>
> As this will cause KVM to execute the following code-path:
> vmx_handle_exit() -> handle_vmcall() -> kvm_emulate_hypercall() -> kvm_pv_send_ipi()
> which will reach out-of-bounds access.
>
> This patch fixes it by adding a check to kvm_pv_send_ipi() against map->max_apic_id,
> ignoring destinations that are not present and delivering the rest. We also check
> whether or not map->phys_map[min + i] is NULL since the max_apic_id is set to the
> max apic id, some phys_map maybe NULL when apic id is sparse, especially kvm
> unconditionally set max_apic_id to 255 to reserve enough space for any xAPIC ID.
>
> Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Reviewed-by: Liran Alon <liran.alon@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Liran Alon <liran.alon@xxxxxxxxxx>
> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
> v1 -> v2:
> * add min > map->max_apic_id check
> * change min to u32
> * add min((u32)BITS_PER_LONG, (map->max_apic_id - min + 1))
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> @@ -548,7 +548,7 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq,
> }
>
> int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
> - unsigned long ipi_bitmap_high, int min,
> + unsigned long ipi_bitmap_high, u32 min,
> unsigned long icr, int op_64_bit)
> {
> int i;
> @@ -571,18 +571,27 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
> rcu_read_lock();
> map = rcu_dereference(kvm->arch.apic_map);
>
> + if (min > map->max_apic_id)
> + goto out;
> /* Bits above cluster_size are masked in the caller. */
> - for_each_set_bit(i, &ipi_bitmap_low, BITS_PER_LONG) {
> - vcpu = map->phys_map[min + i]->vcpu;
> - count += kvm_apic_set_irq(vcpu, &irq, NULL);
> + for_each_set_bit(i, &ipi_bitmap_low,
> + min((u32)BITS_PER_LONG, (map->max_apic_id - min + 1))) {
> + if (map->phys_map[min + i]) {
> + vcpu = map->phys_map[min + i]->vcpu;
> + count += kvm_apic_set_irq(vcpu, &irq, NULL);
> + }
> }
>
> min += cluster_size;
We need a second
if (min > map->max_apic_id)
goto out;
here. I will add it while applying if there are no other change
requests.
> - for_each_set_bit(i, &ipi_bitmap_high, BITS_PER_LONG) {
> - vcpu = map->phys_map[min + i]->vcpu;
> - count += kvm_apic_set_irq(vcpu, &irq, NULL);
> + for_each_set_bit(i, &ipi_bitmap_high,
> + min((u32)BITS_PER_LONG, (map->max_apic_id - min + 1))) {
> + if (map->phys_map[min + i]) {
> + vcpu = map->phys_map[min + i]->vcpu;
> + count += kvm_apic_set_irq(vcpu, &irq, NULL);
> + }
> }
>
> +out:
> rcu_read_unlock();
> return count;
> }
> --
> 2.7.4
>
