x86/HVM: only kill guest when unknown VM exit occurred in guest kernel mode

A recent KVM change by Nadav Amit <namit@cs.technion.ac.il> pointed out
that unconditional VM exits (like VMX'es ones for the INVEPT, INVVPID,
and XSETBV instructions) may result from guest user mode activity (in
the example cases, e.g. prior to a privilege level check being done).
Consequently convert the unconditional domain_crash() to a conditional
one (when guest is in kernel mode) with the alternative of injecting
#UD (when in user mode).

This is meant to be a precaution against in-guest security issues
introduced when any such VM exit becomes possible (on newer hardware)
without the hypervisor immediately being aware of it. There are no such
unhandled VM exits currently (and hence this is not an active security
issue), but old (no longer security maintained) versions exhibit issues
in the cases given as examples above.

Suggested-by: Tim Deegan <tim@xen.org>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index e3e15655c50bcb79337d15c528ff9bb50c0799e6..8aca6e6a34cd20d15cb6310d6818c1e47ec1e615 100644 (file)
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2680,7 +2680,11 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
                  "exitinfo1 = %#"PRIx64", exitinfo2 = %#"PRIx64"\n",
                  exit_reason, 
                  (u64)vmcb->exitinfo1, (u64)vmcb->exitinfo2);
-        domain_crash(v->domain);
+        if ( vmcb_get_cpl(vmcb) )
+            hvm_inject_hw_exception(TRAP_invalid_op,
+                                    HVM_DELIVER_NO_ERROR_CODE);
+        else
+            domain_crash(v->domain);
         break;
     }
 

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 79a69b1d0cf30b703867be234a21cc66fbda0a15..0bf92b25c2435913b828e880e1c30a6a0acc8b4d 100644 (file)
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -3161,8 +3161,19 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
     /* fall through */
     default:
     exit_and_crash:
-        gdprintk(XENLOG_ERR, "Bad vmexit (reason %#lx)\n", exit_reason);
-        domain_crash(v->domain);
+        {
+            struct segment_register ss;
+
+            gdprintk(XENLOG_WARNING, "Bad vmexit (reason %#lx)\n",
+                     exit_reason);
+
+            vmx_get_segment_register(v, x86_seg_ss, &ss);
+            if ( ss.attr.fields.dpl )
+                hvm_inject_hw_exception(TRAP_invalid_op,
+                                        HVM_DELIVER_NO_ERROR_CODE);
+            else
+                domain_crash(v->domain);
+        }
         break;
     }