KVM: x86: Fix TSS size check for 16-bit tasks

A 16-bit TSS is only 44 bytes long. So make sure to test for the correct
size on task switch.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 45aa90f..3c4ca98 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5126,6 +5126,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
        int ret = 0;
        u32 old_tss_base = get_segment_base(vcpu, VCPU_SREG_TR);
        u16 old_tss_sel = get_segment_selector(vcpu, VCPU_SREG_TR);
+       u32 desc_limit;
 
        old_tss_base = kvm_mmu_gva_to_gpa_write(vcpu, old_tss_base, NULL);
 
@@ -5148,7 +5149,10 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
                }
        }
 
-       if (!nseg_desc.p || get_desc_limit(&nseg_desc) < 0x67) {
+       desc_limit = get_desc_limit(&nseg_desc);
+       if (!nseg_desc.p ||
+           ((desc_limit < 0x67 && (nseg_desc.type & 8)) ||
+            desc_limit < 0x2b)) {
                kvm_queue_exception_e(vcpu, TS_VECTOR, tss_selector & 0xfffc);
                return 1;
        }