x86/enter: MACROS to set/clear IBRS and set IBPB

CVE-2017-5715 (Spectre v2 Intel)

Setup macros to control IBRS and IBPB
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(cherry picked from commit 582c3ac1ea2fd287fca743f4e498e844a0e2b606)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

arch/x86/include/asm/spec_ctrl.h

+#ifndef _ASM_X86_SPEC_CTRL_H
+#define _ASM_X86_SPEC_CTRL_H
+
+#include <linux/stringify.h>
+#include <asm/msr-index.h>
+#include <asm/cpufeatures.h>
+#include <asm/alternative-asm.h>
+
+#ifdef __ASSEMBLY__
+
+#define __ASM_ENABLE_IBRS			\
+	pushq %rax;				\
+	pushq %rcx;				\
+	pushq %rdx;				\
+	movl $MSR_IA32_SPEC_CTRL, %ecx;		\
+	movl $0, %edx;				\
+	movl $FEATURE_ENABLE_IBRS, %eax;	\
+	wrmsr;					\
+	popq %rdx;				\
+	popq %rcx;				\
+	popq %rax
+#define __ASM_ENABLE_IBRS_CLOBBER		\
+	movl $MSR_IA32_SPEC_CTRL, %ecx;		\
+	movl $0, %edx;				\
+	movl $FEATURE_ENABLE_IBRS, %eax;	\
+	wrmsr;
+#define __ASM_DISABLE_IBRS			\
+	pushq %rax;				\
+	pushq %rcx;				\
+	pushq %rdx;				\
+	movl $MSR_IA32_SPEC_CTRL, %ecx;		\
+	movl $0, %edx;				\
+	movl $0, %eax;				\
+	wrmsr;					\
+	popq %rdx;				\
+	popq %rcx;				\
+	popq %rax
+
+.macro ENABLE_IBRS
+ALTERNATIVE "", __stringify(__ASM_ENABLE_IBRS), X86_FEATURE_SPEC_CTRL
+.endm
+
+.macro ENABLE_IBRS_CLOBBER
+ALTERNATIVE "", __stringify(__ASM_ENABLE_IBRS_CLOBBER), X86_FEATURE_SPEC_CTRL
+.endm
+
+.macro DISABLE_IBRS
+ALTERNATIVE "", __stringify(__ASM_DISABLE_IBRS), X86_FEATURE_SPEC_CTRL
+.endm
+
+#endif /* __ASSEMBLY__ */
+#endif /* _ASM_X86_SPEC_CTRL_H */