x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support

CVE-2018-3639 (x86)

(cherry picked from commit 20ffa1ca)

Expose indirect_branch_prediction_barrier() for use in subsequent patches.

[ tglx: Add IBPB status to spectre_v2 sysfs file ]
Co-developed-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: ak@linux.intel.com
Cc: ashok.raj@intel.com
Cc: dave.hansen@intel.com
Cc: arjan@linux.intel.com
Cc: torvalds@linux-foundation.org
Cc: peterz@infradead.org
Cc: bp@alien8.de
Cc: pbonzini@redhat.com
Cc: tim.c.chen@linux.intel.com
Cc: gregkh@linux-foundation.org
Link: https://lkml.kernel.org/r/1516896855-7642-8-git-send-email-dwmw@amazon.co.ukSigned-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(backported from commit 31fd9eda linux-4.9.y)
[juergh: This is only a partial backport, hence UBUNTU: SAUCE:!
 - Context adjustments.
 - Drop previous #define X86_FEATURE_IBPB.
 - Don't define indirect_branch_prediction_barrier() (not needed yet in
   Xenial).]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>

arch/x86/include/asm/cpufeatures.h

@@ -200,6 +200,8 @@
 /* Because the ALTERNATIVE scheme is for members of the X86_FEATURE club... */
 #define X86_FEATURE_KAISER     ( 7*32+31) /* CONFIG_PAGE_TABLE_ISOLATION w/o nokaiser */
 
+#define X86_FEATURE_IBPB		( 7*32+21) /* Indirect Branch Prediction Barrier enabled*/
+
 /* Virtualization flags: Linux defined, word 8 */
 #define X86_FEATURE_TPR_SHADOW  ( 8*32+ 0) /* Intel TPR Shadow */
 #define X86_FEATURE_VNMI        ( 8*32+ 1) /* Intel Virtual NMI */
@@ -244,7 +246,6 @@
 
 /* Intel-defined CPU QoS Sub-leaf, CPUID level 0x0000000F:0 (edx), word 11 */
 #define X86_FEATURE_CQM_LLC	(11*32+ 1) /* LLC QoS if 1 */
-#define X86_FEATURE_IBPB	(13*32+12) /* Indirect Branch Prediction Barrier */
 
 /* Intel-defined CPU QoS Sub-leaf, CPUID level 0x0000000F:1 (edx), word 12 */
 #define X86_FEATURE_CQM_OCCUP_LLC (12*32+ 0) /* LLC occupancy monitoring if 1 */

arch/x86/kernel/cpu/bugs.c

@@ -280,6 +280,13 @@ static void __init spectre_v2_select_mitigation(void)
 	spectre_v2_enabled = mode;
 	pr_info("%s\n", spectre_v2_strings[mode]);
 
+	/* Initialize Indirect Branch Prediction Barrier if supported */
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL) ||
+	    boot_cpu_has(X86_FEATURE_AMD_PRED_CMD)) {
+		setup_force_cpu_cap(X86_FEATURE_IBPB);
+		pr_info("Enabling Indirect Branch Prediction Barrier\n");
+	}
+
 	pr_info("Speculation control IBPB %s IBRS %s",
 	        ibpb_supported ? "supported" : "not-supported",
 	        ibrs_supported ? "supported" : "not-supported");