KVM: LAPIC: Fix pv ipis out-of-bounds access
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@oracle.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
[Add second "if (min > map->max_apic_id)" to complete the fix. -Radim]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3ad10f6..8e90488 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1455,7 +1455,7 @@
void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu);
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);
u64 kvm_get_arch_capabilities(void);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0cefba2..17c0472 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -548,7 +548,7 @@
}
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 +571,31 @@
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;
- 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);
+
+ if (min > map->max_apic_id)
+ goto out;
+
+ 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;
}