x86/spec_ctrl: Add lock to serialize changes to ibrs and ibpb control

CVE-2017-5715 (Spectre v2 Intel)
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(backported from commit 33e16ee8bd43aa4f065e17abbe9ed66457327b84)
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/kernel/cpu/intel.c

@@ -529,16 +529,18 @@ static void init_intel(struct cpuinfo_x86 *c)
 
 	init_intel_energy_perf(c);
 
-	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
-                printk_once(KERN_INFO "FEATURE SPEC_CTRL Present\n");
-		set_ibrs_supported();
-		set_ibpb_supported();
-		if (ibrs_inuse)
-			sysctl_ibrs_enabled = 1;
-		if (ibpb_inuse)
-			sysctl_ibpb_enabled = 1;
-        } else {
-                printk_once(KERN_INFO "FEATURE SPEC_CTRL Not Present\n");
+	if (!c->cpu_index) {
+		if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
+			printk(KERN_INFO "FEATURE SPEC_CTRL Present\n");
+			set_ibrs_supported();
+			set_ibpb_supported();
+			if (ibrs_inuse)
+				sysctl_ibrs_enabled = 1;
+			if (ibpb_inuse)
+				sysctl_ibpb_enabled = 1;
+		} else {
+			printk(KERN_INFO "FEATURE SPEC_CTRL Not Present\n");
+		}
 	}
 }
 

arch/x86/kernel/cpu/microcode/core.c

@@ -422,12 +422,14 @@ static ssize_t reload_store(struct device *dev,
 
 	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
 		printk_once(KERN_INFO "FEATURE SPEC_CTRL Present\n");
+		mutex_lock(&spec_ctrl_mutex);
 		set_ibrs_supported();
 		set_ibpb_supported();
 		if (ibrs_inuse)
 			sysctl_ibrs_enabled = 1;
 		if (ibpb_inuse)
 			sysctl_ibpb_enabled = 1;
+		mutex_unlock(&spec_ctrl_mutex);
 	}
 
 	mutex_unlock(&microcode_mutex);

kernel/smp.c

@@ -520,6 +520,10 @@ int use_ibpb;
 EXPORT_SYMBOL(use_ibpb);
 #endif
 
+/* mutex to serialize IBRS & IBPB control changes */
+DEFINE_MUTEX(spec_ctrl_mutex);
+EXPORT_SYMBOL(spec_ctrl_mutex);
+
 /*
  * Setup routine for controlling SMP activation
  *

kernel/sysctl.c

@@ -69,6 +69,7 @@
 #include <linux/mount.h>
 
 #include <asm/uaccess.h>
+#include <linux/mutex.h>
 #include <asm/processor.h>
 
 #ifdef CONFIG_X86
@@ -2424,12 +2425,17 @@ int proc_dointvec_minmax(struct ctl_table *table, int write,
 int proc_dointvec_ibrs_dump(struct ctl_table *table, int write,
 	void __user *buffer, size_t *lenp, loff_t *ppos)
 {
-	int ret;
+	int ret, orig_inuse;
 	unsigned int cpu;
 
+
 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	printk("sysctl_ibrs_enabled = %u, sysctl_ibpb_enabled = %u\n", sysctl_ibrs_enabled, sysctl_ibpb_enabled);
 	printk("use_ibrs = %d, use_ibpb = %d\n", use_ibrs, use_ibpb);
+	mutex_lock(&spec_ctrl_mutex);
+	orig_inuse = use_ibrs;
+	/* temporary halt to ibrs usage to dump ibrs values */
+	clear_ibrs_inuse();
 	for_each_online_cpu(cpu) {
 	       u64 val;
 
@@ -2439,6 +2445,8 @@ int proc_dointvec_ibrs_dump(struct ctl_table *table, int write,
 		       val = 0;
 	       printk("read cpu %d ibrs val %lu\n", cpu, (unsigned long) val);
 	}
+	use_ibrs = orig_inuse;
+	mutex_unlock(&spec_ctrl_mutex);
 	return ret;
 }
 
@@ -2451,6 +2459,7 @@ int proc_dointvec_ibrs_ctrl(struct ctl_table *table, int write,
 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	pr_debug("sysctl_ibrs_enabled = %u, sysctl_ibpb_enabled = %u\n", sysctl_ibrs_enabled, sysctl_ibpb_enabled);
 	pr_debug("before:use_ibrs = %d, use_ibpb = %d\n", use_ibrs, use_ibpb);
+	mutex_lock(&spec_ctrl_mutex);
 	if (sysctl_ibrs_enabled == 0) {
 		/* always set IBRS off */
 		set_ibrs_disabled();
@@ -2474,6 +2483,7 @@ int proc_dointvec_ibrs_ctrl(struct ctl_table *table, int write,
 			/* platform don't support ibrs */
 			sysctl_ibrs_enabled = 0;
 	}
+	mutex_unlock(&spec_ctrl_mutex);
 	pr_debug("after:use_ibrs = %d, use_ibpb = %d\n", use_ibrs, use_ibpb);
 	return ret;
 }
@@ -2486,6 +2496,7 @@ int proc_dointvec_ibpb_ctrl(struct ctl_table *table, int write,
 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	pr_debug("sysctl_ibrs_enabled = %u, sysctl_ibpb_enabled = %u\n", sysctl_ibrs_enabled, sysctl_ibpb_enabled);
 	pr_debug("before:use_ibrs = %d, use_ibpb = %d\n", use_ibrs, use_ibpb);
+	mutex_lock(&spec_ctrl_mutex);
 	if (sysctl_ibpb_enabled == 0)
 		set_ibpb_disabled();
 	else if (sysctl_ibpb_enabled == 1) {
@@ -2494,6 +2505,7 @@ int proc_dointvec_ibpb_ctrl(struct ctl_table *table, int write,
 			/* platform don't support ibpb */
 			sysctl_ibpb_enabled = 0;
 	}
+	mutex_unlock(&spec_ctrl_mutex);
 	pr_debug("after:use_ibrs = %d, use_ibpb = %d\n", use_ibrs, use_ibpb);
 	return ret;
 }