Re: [Xen-devel] [PATCH v2 3/3] x86/HVM: don't crash guest upon problems occurring in user mode

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/11/14 15:37, Jan Beulich wrote:

This extends commit 5283b310 ("x86/HVM: only kill guest when unknown VM
exit occurred in guest kernel mode") to a few more cases, including the
failed VM entry one that XSA-110 was needed to be issued for.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

---
v2: - s/crash_or_gp/crash_or_fault/
    - drop changes to svm_do_nested_pgfault(), svm_vmexit_handler()'s
      VMEXIT_NPF handling, and ept_handle_violation()

--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -90,6 +90,15 @@ static bool_t amd_erratum383_found __rea
 static uint64_t osvw_length, osvw_status;
 static DEFINE_SPINLOCK(osvw_lock);
 
+/* Only crash the guest if the problem originates in kernel mode. */
+static void svm_crash_or_fault(struct vcpu *v)
+{
+    if ( vmcb_get_cpl(v->arch.hvm_svm.vmcb) )
+        hvm_inject_hw_exception(TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE);
+    else
+        domain_crash(v->domain);
+}
+
 void __update_guest_eip(struct cpu_user_regs *regs, unsigned int inst_len)
 {
     struct vcpu *curr = current;
@@ -100,7 +109,7 @@ void __update_guest_eip(struct cpu_user_
     if ( unlikely(inst_len > 15) )
     {
         gdprintk(XENLOG_ERR, "Bad instruction length %u\n", inst_len);
-        domain_crash(curr->domain);
+        svm_crash_or_fault(curr);
         return;
     }
 
@@ -2680,11 +2689,7 @@ void svm_vmexit_handler(struct cpu_user_
                  "exitinfo1 = %#"PRIx64", exitinfo2 = %#"PRIx64"\n",
                  exit_reason, 
                  (u64)vmcb->exitinfo1, (u64)vmcb->exitinfo2);
-        if ( vmcb_get_cpl(vmcb) )
-            hvm_inject_hw_exception(TRAP_invalid_op,
-                                    HVM_DELIVER_NO_ERROR_CODE);
-        else
-            domain_crash(v->domain);
+        svm_crash_or_fault(v);
         break;
     }
 
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -134,6 +134,18 @@ static void vmx_vcpu_destroy(struct vcpu
     passive_domain_destroy(v);
 }
 
+/* Only crash the guest if the problem originates in kernel mode. */
+static void vmx_crash_or_fault(struct vcpu *v)
+{
+    struct segment_register ss;
+
+    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);
+}
+
 static DEFINE_PER_CPU(struct vmx_msr_state, host_msr_state);
 
 static const u32 msr_index[] =
@@ -2508,7 +2520,7 @@ static void vmx_failed_vmentry(unsigned 
     vmcs_dump_vcpu(curr);
     printk("**************************************\n");
 
-    domain_crash(curr->domain);
+    vmx_crash_or_fault(curr);
 }
 
 void vmx_enter_realmode(struct cpu_user_regs *regs)
@@ -3161,19 +3173,8 @@ void vmx_vmexit_handler(struct cpu_user_
     /* fall through */
     default:
     exit_and_crash:
-        {
-            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);
-        }
+        gdprintk(XENLOG_WARNING, "Bad vmexit (reason %#lx)\n", exit_reason);
+        vmx_crash_or_fault(v);
         break;
     }
 

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