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

(Cherry-picked from commit e8861cfe2c75bdce36655b64d7ce02c2b31b604d)

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e0f010e53f63..dd7892740314 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4576,6 +4576,7 @@ 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 = vcpu->arch.mmu.gva_to_gpa(vcpu, old_tss_base);
 
@@ -4598,7 +4599,10 @@ 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;
         }