Re: [PATCH] KVM: LAPIC: Fix pv ipis out-of-bounds access

Radim Krcmar
2018-08-29T13:55:40Z

2018-08-29 13:43+0300, Liran Alon:
> Why is “min” defined as “int” instead of “unsigned int”?
> It represents the lowest APIC ID in bitmap so it can’t be negative…

Right,

I think the code would look better as something like (untested):

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0cefba28c864..24fc84eb97d2 100644
--- 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;
@@ -557,6 +557,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
struct kvm_lapic_irq irq = {0};
int cluster_size = op_64_bit ? 64 : 32;
int count = 0;
+ unsigned long ipi_bitmap[2] = {ipi_bitmap_low, ipi_bitmap_high};

irq.vector = icr & APIC_VECTOR_MASK;
irq.delivery_mode = icr & APIC_MODE_MASK;
@@ -571,16 +572,14 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
rcu_read_lock();
map = rcu_dereference(kvm->arch.apic_map);

- /* 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);
- }
+ if (min <= map->max_apic_id) {
+ size_t ipi_bitmap_size = MIN(sizeof(ipi_bitmap) * 8,
+ map->max_apic_id - min + 1);

- min += cluster_size;
- 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, ipi_bitmap_size) {
+ vcpu = map->phys_map[min + i]->vcpu;
+ count += kvm_apic_set_irq(vcpu, &irq, NULL);
+ }
}

rcu_read_unlock();