Add definition for Intel Speculative Store Bypass Disable MSR bits

Security:	CVE-2018-3639
Sponsored by:	The FreeBSD Foundation
MFC after:	3 days

sys/x86/include/specialreg.h

@@ -428,10 +428,12 @@
 #define	CPUID_STDEXT3_IBPB	0x04000000
 #define	CPUID_STDEXT3_STIBP	0x08000000
 #define	CPUID_STDEXT3_ARCH_CAP	0x20000000
+#define	CPUID_STDEXT3_SSBD	0x80000000
 
 /* MSR IA32_ARCH_CAP(ABILITIES) bits */
 #define	IA32_ARCH_CAP_RDCL_NO	0x00000001
 #define	IA32_ARCH_CAP_IBRS_ALL	0x00000002
+#define	IA32_ARCH_CAP_SSBD_NO	0x00000004
 
 /*
  * CPUID manufacturers identifiers
@@ -704,6 +706,7 @@
 /* MSR IA32_SPEC_CTRL */
 #define	IA32_SPEC_CTRL_IBRS	0x00000001
 #define	IA32_SPEC_CTRL_STIBP	0x00000002
+#define	IA32_SPEC_CTRL_SSBD	0x00000004
 
 /* MSR IA32_PRED_CMD */
 #define	IA32_PRED_CMD_IBPB_BARRIER	0x0000000000000001ULL

sys/x86/x86/identcpu.c

@@ -990,6 +990,7 @@ printcpuinfo(void)
 				       "\033IBPB"
 				       "\034STIBP"
 				       "\036ARCH_CAP"
+				       "\040SSBD"
 				       );
 			}