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KVM: LAPIC: Fix pv ipis out-of-bounds access

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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>
This commit is contained in:
Wanpeng Li 2018-08-30 10:03:30 +08:00 committed by Radim Krčmář
parent b5861e5cf2
commit bdf7ffc899
2 changed files with 21 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/kvm_host.h
View File

@ -1455,7 +1455,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
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);

27
arch/x86/kvm/lapic.c
View File

@ -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 +571,31 @@ 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;
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;
}