x86/vmscape: Enable the mitigation

commit 556c1ad666ad90c50ec8fccb930dd5046cfbecfb upstream.

Enable the previously added mitigation for VMscape. Add the cmdline
vmscape={off|ibpb|force} and sysfs reporting.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Amit Shah <amit.shah@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 86 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3b9ba4b227d5..68a7a1d989f9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2537,6 +2537,15 @@ config MITIGATION_TSA
 	  security vulnerability on AMD CPUs which can lead to forwarding of
 	  invalid info to subsequent instructions and thus can affect their
 	  timing and thereby cause a leakage.
+
+config MITIGATION_VMSCAPE
+	bool "Mitigate VMSCAPE"
+	depends on KVM
+	default y
+	help
+	  Enable mitigation for VMSCAPE attacks. VMSCAPE is a hardware security
+	  vulnerability on Intel and AMD CPUs that may allow a guest to do
+	  Spectre v2 style attacks on userspace hypervisor.
 endif
 
 config ARCH_HAS_ADD_PAGES
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index dd3379c00c4a..f317f87d1681 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -50,6 +50,7 @@ static void __init gds_select_mitigation(void);
 static void __init srso_select_mitigation(void);
 static void __init its_select_mitigation(void);
 static void __init tsa_select_mitigation(void);
+static void __init vmscape_select_mitigation(void);
 
 /* The base value of the SPEC_CTRL MSR without task-specific bits set */
 u64 x86_spec_ctrl_base;
@@ -193,6 +194,7 @@ void __init cpu_select_mitigations(void)
 	gds_select_mitigation();
 	its_select_mitigation();
 	tsa_select_mitigation();
+	vmscape_select_mitigation();
 }
 
 /*
@@ -2899,6 +2901,68 @@ pred_cmd:
 }
 
 #undef pr_fmt
+#define pr_fmt(fmt)	"VMSCAPE: " fmt
+
+enum vmscape_mitigations {
+	VMSCAPE_MITIGATION_NONE,
+	VMSCAPE_MITIGATION_AUTO,
+	VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER,
+	VMSCAPE_MITIGATION_IBPB_ON_VMEXIT,
+};
+
+static const char * const vmscape_strings[] = {
+	[VMSCAPE_MITIGATION_NONE]		= "Vulnerable",
+	/* [VMSCAPE_MITIGATION_AUTO] */
+	[VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER]	= "Mitigation: IBPB before exit to userspace",
+	[VMSCAPE_MITIGATION_IBPB_ON_VMEXIT]	= "Mitigation: IBPB on VMEXIT",
+};
+
+static enum vmscape_mitigations vmscape_mitigation __ro_after_init =
+	IS_ENABLED(CONFIG_MITIGATION_VMSCAPE) ? VMSCAPE_MITIGATION_AUTO : VMSCAPE_MITIGATION_NONE;
+
+static int __init vmscape_parse_cmdline(char *str)
+{
+	if (!str)
+		return -EINVAL;
+
+	if (!strcmp(str, "off")) {
+		vmscape_mitigation = VMSCAPE_MITIGATION_NONE;
+	} else if (!strcmp(str, "ibpb")) {
+		vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER;
+	} else if (!strcmp(str, "force")) {
+		setup_force_cpu_bug(X86_BUG_VMSCAPE);
+		vmscape_mitigation = VMSCAPE_MITIGATION_AUTO;
+	} else {
+		pr_err("Ignoring unknown vmscape=%s option.\n", str);
+	}
+
+	return 0;
+}
+early_param("vmscape", vmscape_parse_cmdline);
+
+static void __init vmscape_select_mitigation(void)
+{
+	if (cpu_mitigations_off() ||
+	    !boot_cpu_has_bug(X86_BUG_VMSCAPE) ||
+	    !boot_cpu_has(X86_FEATURE_IBPB)) {
+		vmscape_mitigation = VMSCAPE_MITIGATION_NONE;
+		return;
+	}
+
+	if (vmscape_mitigation == VMSCAPE_MITIGATION_AUTO)
+		vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER;
+
+	if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB ||
+	    srso_mitigation == SRSO_MITIGATION_IBPB_ON_VMEXIT)
+		vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_ON_VMEXIT;
+
+	if (vmscape_mitigation == VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER)
+		setup_force_cpu_cap(X86_FEATURE_IBPB_EXIT_TO_USER);
+
+	pr_info("%s\n", vmscape_strings[vmscape_mitigation]);
+}
+
+#undef pr_fmt
 #define pr_fmt(fmt) fmt
 
 #ifdef CONFIG_SYSFS
@@ -3146,6 +3210,11 @@ static ssize_t tsa_show_state(char *buf)
 	return sysfs_emit(buf, "%s\n", tsa_strings[tsa_mitigation]);
 }
 
+static ssize_t vmscape_show_state(char *buf)
+{
+	return sysfs_emit(buf, "%s\n", vmscape_strings[vmscape_mitigation]);
+}
+
 static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
 			       char *buf, unsigned int bug)
 {
@@ -3210,6 +3279,9 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 	case X86_BUG_TSA:
 		return tsa_show_state(buf);
 
+	case X86_BUG_VMSCAPE:
+		return vmscape_show_state(buf);
+
 	default:
 		break;
 	}
@@ -3299,4 +3371,9 @@ ssize_t cpu_show_tsa(struct device *dev, struct device_attribute *attr, char *bu
 {
 	return cpu_show_common(dev, attr, buf, X86_BUG_TSA);
 }
+
+ssize_t cpu_show_vmscape(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return cpu_show_common(dev, attr, buf, X86_BUG_VMSCAPE);
+}
 #endif