arm64: add sysfs vulnerability show for spectre-v2

Track whether all the cores in the machine are vulnerable to Spectre-v2,
and whether all the vulnerable cores have been mitigated. We then expose
this information to userspace via sysfs.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index a9c3ad4f794865c99b54df36347244676c93c429..d2bbafa04b3c7817605c618c57ccbdee9261c2b8 100644 (file)
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -512,6 +512,10 @@ cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
        .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,                 \
        CAP_MIDR_RANGE_LIST(midr_list)
 
+/* Track overall mitigation state. We are only mitigated if all cores are ok */
+static bool __hardenbp_enab = true;
+static bool __spectrev2_safe = true;
+
 /*
  * List of CPUs that do not need any Spectre-v2 mitigation at all.
  */
@@ -522,6 +526,10 @@ static const struct midr_range spectre_v2_safe_list[] = {
        { /* sentinel */ }
 };
 
+/*
+ * Track overall bp hardening for all heterogeneous cores in the machine.
+ * We are only considered "safe" if all booted cores are known safe.
+ */
 static bool __maybe_unused
 check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
 {
@@ -543,6 +551,8 @@ check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
        if (!need_wa)
                return false;
 
+       __spectrev2_safe = false;
+
        if (!IS_ENABLED(CONFIG_HARDEN_BRANCH_PREDICTOR)) {
                pr_warn_once("spectrev2 mitigation disabled by kernel configuration\n");
                __hardenbp_enab = false;
@@ -552,11 +562,14 @@ check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
        /* forced off */
        if (__nospectre_v2) {
                pr_info_once("spectrev2 mitigation disabled by command line option\n");
+               __hardenbp_enab = false;
                return false;
        }
 
-       if (need_wa < 0)
+       if (need_wa < 0) {
                pr_warn_once("ARM_SMCCC_ARCH_WORKAROUND_1 missing from firmware\n");
+               __hardenbp_enab = false;
+       }
 
        return (need_wa > 0);
 }
@@ -779,3 +792,15 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
 {
        return sprintf(buf, "Mitigation: __user pointer sanitization\n");
 }
+
+ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
+               char *buf)
+{
+       if (__spectrev2_safe)
+               return sprintf(buf, "Not affected\n");
+
+       if (__hardenbp_enab)
+               return sprintf(buf, "Mitigation: Branch predictor hardening\n");
+
+       return sprintf(buf, "Vulnerable\n");
+}