KVM: VMX: Fix %ds/%es clobber

The vmx exit code unconditionally restores %ds and %es to __USER_DS.  This
can override the user's values, since %ds and %es are not saved and restored
in x86_64 syscalls.  In practice, this isn't dangerous since nobody uses
segment registers in long mode, least of all programs that use KVM.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3062ea95266ea6cf6b8ed500ea0bb11846386238..f2ee016e1004af6fd9a2727f17b8b0a76a9c8760 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6102,7 +6102,10 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
 static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 {
        struct vcpu_vmx *vmx = to_vmx(vcpu);
+       u16 _ds, _es;
 
+       savesegment(ds, _ds);
+       savesegment(es, _es);
        if (is_guest_mode(vcpu) && !vmx->nested.nested_run_pending) {
                struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
                if (vmcs12->idt_vectoring_info_field &
@@ -6263,7 +6266,8 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
                }
        }
 
-       asm("mov %0, %%ds; mov %0, %%es" : : "r"(__USER_DS));
+       loadsegment(ds, _ds);
+       loadsegment(es, _es);
        vmx->loaded_vmcs->launched = 1;
 
        vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);