KVM: VMX: Check cpl before emulating debug register access

Debug registers may only be accessed from cpl 0.  Unfortunately, vmx will
code to emulate the instruction even though it was issued from guest
userspace, possibly leading to an unexpected trap later.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7627ff607a90..4137cc579ba5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -223,6 +223,19 @@ void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
 EXPORT_SYMBOL_GPL(kvm_queue_exception_e);
 
 /*
+ * Checks if cpl <= required_cpl; if true, return true.  Otherwise queue
+ * a #GP and return false.
+ */
+bool kvm_require_cpl(struct kvm_vcpu *vcpu, int required_cpl)
+{
+        if (kvm_x86_ops->get_cpl(vcpu) <= required_cpl)
+                return true;
+        kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
+        return false;
+}
+EXPORT_SYMBOL_GPL(kvm_require_cpl);
+
+/*
  * Load the pae pdptrs.  Return true is they are all valid.
  */
 int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3)