[PATCH 4/4] KVM: x86: lapic: don't allow to set non default apic id when not using x2apic api

Maxim Levitsky
2022-03-01T13:56:11Z

Fix a loop hole in setting the apic state that didn't check if
apic id == vcpu_id when x2apic is enabled but userspace is using
a older variant of the ioctl which didn't had 32 bit apic ids.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/lapic.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 80a2020c4db40..8d35f56c64020 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2618,15 +2618,14 @@ static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
u32 *ldr = (u32 *)(s->regs + APIC_LDR);
u64 icr;

- if (vcpu->kvm->arch.x2apic_format) {
- if (*id != vcpu->vcpu_id)
- return -EINVAL;
- } else {
- if (set)
- *id >>= 24;
- else
- *id <<= 24;
- }
+ if (!vcpu->kvm->arch.x2apic_format && set)
+ *id >>= 24;
+
+ if (*id != vcpu->vcpu_id)
+ return -EINVAL;
+
+ if (!vcpu->kvm->arch.x2apic_format && !set)
+ *id <<= 24;

/*
* In x2APIC mode, the LDR is fixed and based on the id. And
--
2.26.3