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KVM: selftests: Add a testcase to verify x2APIC is fully readonly

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Add a test to verify that userspace can't change a vCPU's x2APIC ID by
abusing KVM_SET_LAPIC.  KVM models the x2APIC ID (and x2APIC LDR) as
readonly, and silently ignores userspace attempts to change the x2APIC ID
for backwards compatibility.

Signed-off-by: Michal Luczaj <mhal@rbox.co>
[sean: write changelog, add to existing test]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240802202941.344889-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Michal Luczaj 2024-08-02 13:29:41 -07:00 committed by Paolo Bonzini
parent 4b7c3f6d04
commit 238d3d63d1
1 changed files with 28 additions and 0 deletions
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28
tools/testing/selftests/kvm/x86_64/xapic_state_test.c
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@ -184,6 +184,33 @@ static void test_apic_id(void)
kvm_vm_free(vm);
}
static void test_x2apic_id(void)
{
struct kvm_lapic_state lapic = {};
struct kvm_vcpu *vcpu;
struct kvm_vm *vm;
int i;
vm = vm_create_with_one_vcpu(&vcpu, NULL);
vcpu_set_msr(vcpu, MSR_IA32_APICBASE, MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE);
/*
* Try stuffing a modified x2APIC ID, KVM should ignore the value and
* always return the vCPU's default/readonly x2APIC ID.
*/
for (i = 0; i <= 0xff; i++) {
*(u32 *)(lapic.regs + APIC_ID) = i << 24;
*(u32 *)(lapic.regs + APIC_SPIV) = APIC_SPIV_APIC_ENABLED;
vcpu_ioctl(vcpu, KVM_SET_LAPIC, &lapic);
vcpu_ioctl(vcpu, KVM_GET_LAPIC, &lapic);
TEST_ASSERT(*((u32 *)&lapic.regs[APIC_ID]) == vcpu->id << 24,
"x2APIC ID should be fully readonly");
}
kvm_vm_free(vm);
}
int main(int argc, char *argv[])
{
struct xapic_vcpu x = {
@ -211,4 +238,5 @@ int main(int argc, char *argv[])
kvm_vm_free(vm);
test_apic_id();
test_x2apic_id();
}