KVM: Allow emulation of syscalls instructions on #UD

Add the opcodes for syscall, sysenter and sysexit to the list of instructions
handled by the undefined opcode handler.

Signed-off-by: Christoph Egger <christoph.egger@amd.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 892a7a6..57e76b3 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2667,14 +2667,33 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 
                r = x86_decode_insn(&vcpu->arch.emulate_ctxt, &emulate_ops);
 
-               /* Reject the instructions other than VMCALL/VMMCALL when
-                * try to emulate invalid opcode */
+               /* Only allow emulation of specific instructions on #UD
+                * (namely VMMCALL, sysenter, sysexit, syscall)*/
                c = &vcpu->arch.emulate_ctxt.decode;
-               if ((emulation_type & EMULTYPE_TRAP_UD) &&
-                   (!(c->twobyte && c->b == 0x01 &&
-                     (c->modrm_reg == 0 || c->modrm_reg == 3) &&
-                      c->modrm_mod == 3 && c->modrm_rm == 1)))
-                       return EMULATE_FAIL;
+               if (emulation_type & EMULTYPE_TRAP_UD) {
+                       if (!c->twobyte)
+                               return EMULATE_FAIL;
+                       switch (c->b) {
+                       case 0x01: /* VMMCALL */
+                               if (c->modrm_mod != 3 || c->modrm_rm != 1)
+                                       return EMULATE_FAIL;
+                               break;
+                       case 0x34: /* sysenter */
+                       case 0x35: /* sysexit */
+                               if (c->modrm_mod != 0 || c->modrm_rm != 0)
+                                       return EMULATE_FAIL;
+                               break;
+                       case 0x05: /* syscall */
+                               if (c->modrm_mod != 0 || c->modrm_rm != 0)
+                                       return EMULATE_FAIL;
+                               break;
+                       default:
+                               return EMULATE_FAIL;
+                       }
+
+                       if (!(c->modrm_reg == 0 || c->modrm_reg == 3))
+                               return EMULATE_FAIL;
+               }
 
                ++vcpu->stat.insn_emulation;
                if (r)  {