[Xen-devel] [PATCH 6/7] x86emul: vendor specific SYSCALL behavior

[Jan Beulich <jbeulich@xxxxxxxx>]

AMD CPUs permit the insn everywhere (even outside of protected mode),
while Intel ones restrict it to 64-bit mode. While at it also add the
so far missing CPUID bit check.

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

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1870,6 +1870,7 @@ amd_like(const struct x86_emulate_ctxt *
 #define vcpu_has_f16c()        (ctxt->cpuid->basic.f16c)
 #define vcpu_has_rdrand()      (ctxt->cpuid->basic.rdrand)
 
+#define vcpu_has_syscall()     (ctxt->cpuid->extd.syscall)
 #define vcpu_has_mmxext()      (ctxt->cpuid->extd.mmxext || vcpu_has_sse())
 #define vcpu_has_3dnow_ext()   (ctxt->cpuid->extd._3dnowext)
 #define vcpu_has_3dnow()       (ctxt->cpuid->extd._3dnow)
@@ -5897,13 +5898,13 @@ x86_emulate(
         break;
 
     case X86EMUL_OPC(0x0f, 0x05): /* syscall */
-        generate_exception_if(!in_protmode(ctxt, ops), EXC_UD);
-
+        vcpu_must_have(syscall);
         /* Inject #UD if syscall/sysret are disabled. */
         fail_if(ops->read_msr == NULL);
         if ( (rc = ops->read_msr(MSR_EFER, &msr_val, ctxt)) != X86EMUL_OKAY )
             goto done;
         generate_exception_if((msr_val & EFER_SCE) == 0, EXC_UD);
+        generate_exception_if(!amd_like(ctxt) && !mode_64bit(), EXC_UD);
 
         if ( (rc = ops->read_msr(MSR_STAR, &msr_val, ctxt)) != X86EMUL_OKAY )
             goto done;