arm64: KVM: Propagate full Spectre v2 workaround state to KVM guests

Recent commits added the explicit notion of "workaround not required" to
the state of the Spectre v2 (aka. BP_HARDENING) workaround, where we
just had "needed" and "unknown" before.

Export this knowledge to the rest of the kernel and enhance the existing
kvm_arm_harden_branch_predictor() to report this new state as well.
Export this new state to guests when they use KVM's firmware interface
emulation.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 18 insertions, 5 deletions

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index ca11ff7bf55e..1e43ba5c79b7 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -554,6 +554,17 @@ cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
 static bool __hardenbp_enab = true;
 static bool __spectrev2_safe = true;
 
+int get_spectre_v2_workaround_state(void)
+{
+	if (__spectrev2_safe)
+		return ARM64_BP_HARDEN_NOT_REQUIRED;
+
+	if (!__hardenbp_enab)
+		return ARM64_BP_HARDEN_UNKNOWN;
+
+	return ARM64_BP_HARDEN_WA_NEEDED;
+}
+
 /*
  * List of CPUs that do not need any Spectre-v2 mitigation at all.
  */
@@ -854,13 +865,15 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
 ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
 		char *buf)
 {
-	if (__spectrev2_safe)
+	switch (get_spectre_v2_workaround_state()) {
+	case ARM64_BP_HARDEN_NOT_REQUIRED:
 		return sprintf(buf, "Not affected\n");
-
-	if (__hardenbp_enab)
+        case ARM64_BP_HARDEN_WA_NEEDED:
 		return sprintf(buf, "Mitigation: Branch predictor hardening\n");
-
-	return sprintf(buf, "Vulnerable\n");
+        case ARM64_BP_HARDEN_UNKNOWN:
+	default:
+		return sprintf(buf, "Vulnerable\n");
+	}
 }
 
 ssize_t cpu_show_spec_store_bypass(struct device *dev,