Patch "[Variant 2/Spectre-v2] arm64: KVM: Report SMCCC_ARCH_WORKAROUND_1 BP hardening support" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

[Variant 2/Spectre-v2] arm64: KVM: Report SMCCC_ARCH_WORKAROUND_1 BP hardening support

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-kvm-report-smccc_arch_workaround_1-bp-hardening-support.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marc Zyngier <[email protected]>
Date: Tue, 6 Feb 2018 17:56:14 +0000
Subject: [Variant 2/Spectre-v2] arm64: KVM: Report SMCCC_ARCH_WORKAROUND_1 BP hardening support

From: Marc Zyngier <[email protected]>

Commit 6167ec5c9145 upstream.

A new feature of SMCCC 1.1 is that it offers firmware-based CPU workarounds. In particular, SMCCC_ARCH_WORKAROUND_1 provides BP hardening for CVE-2017-5715.

If the host has some mitigation for this issue, report that we deal with it using SMCCC_ARCH_WORKAROUND_1, as we apply the host workaround on every guest exit.

Conflicts:
arch/arm/include/asm/kvm_host.h
arch/arm64/include/asm/kvm_host.h

---
 arch/arm/include/asm/kvm_host.h   |    6 ++++++
 arch/arm64/include/asm/kvm_host.h |    5 +++++
 include/linux/arm-smccc.h         |    5 +++++
 virt/kvm/arm/psci.c               |    9 ++++++++-
 4 files changed, 24 insertions(+), 1 deletion(-)

@@ -301,4 +301,10 @@ int kvm_arm_vcpu_arch_has_attr(struct kv
 /* All host FP/SIMD state is restored on guest exit, so nothing to save: */
 static inline void kvm_fpsimd_flush_cpu_state(void) {}
 
+static inline bool kvm_arm_harden_branch_predictor(void)
+{
+	/* No way to detect it yet, pretend it is not there. */
+	return false;
+}
+
 #endif /* __ARM_KVM_HOST_H__ */

@@ -396,4 +396,9 @@ static inline void kvm_fpsimd_flush_cpu_
 		sve_flush_cpu_state();
 }
 
+static inline bool kvm_arm_harden_branch_predictor(void)
+{
+	return cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR);
+}
+
 #endif /* __ARM64_KVM_HOST_H__ */

@@ -73,6 +73,11 @@
 			   ARM_SMCCC_SMC_32,				\
 			   0, 1)
 
+#define ARM_SMCCC_ARCH_WORKAROUND_1					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   0, 0x8000)
+
 #ifndef __ASSEMBLY__
 
 #include <linux/linkage.h>

@@ -405,13 +405,20 @@ int kvm_hvc_call_handler(struct kvm_vcpu
 {
 	u32 func_id = smccc_get_function(vcpu);
 	u32 val = PSCI_RET_NOT_SUPPORTED;
+	u32 feature;
 
 	switch (func_id) {
 	case ARM_SMCCC_VERSION_FUNC_ID:
 		val = ARM_SMCCC_VERSION_1_1;
 		break;
 	case ARM_SMCCC_ARCH_FEATURES_FUNC_ID:
-		/* Nothing supported yet */
+		feature = smccc_get_arg1(vcpu);
+		switch(feature) {
+		case ARM_SMCCC_ARCH_WORKAROUND_1:
+			if (kvm_arm_harden_branch_predictor())
+				val = 0;
+			break;
+		}
 		break;
 	default:
 		return kvm_psci_call(vcpu);

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/arm-arm64-smccc-make-function-identifiers-an-unsigned-quantity.patch queue-4.15/arm64-move-bp-hardening-to-check_and_switch_context.patch queue-4.15/arm-arm64-kvm-advertise-smccc-v1.1.patch queue-4.15/arm64-move-post_ttbr_update_workaround-to-c-code.patch queue-4.15/firmware-psci-expose-psci-conduit.patch queue-4.15/arm64-force-kpti-to-be-disabled-on-cavium-thunderx.patch queue-4.15/arm64-entry-apply-bp-hardening-for-high-priority-synchronous-exceptions.patch queue-4.15/arm64-kpti-fix-the-interaction-between-asid-switching-and-software-pan.patch queue-4.15/firmware-psci-expose-smccc-version-through-psci_ops.patch queue-4.15/arm64-implement-branch-predictor-hardening-for-affected-cortex-a-cpus.patch queue-4.15/arm-arm64-kvm-add-psci_version-helper.patch queue-4.15/arm64-kill-psci_get_version-as-a-variant-2-workaround.patch queue-4.15/arm64-entry-apply-bp-hardening-for-suspicious-interrupts-from-el0.patch queue-4.15/arm64-capabilities-handle-duplicate-entries-for-a-capability.patch queue-4.15/arm64-add-arm_smccc_arch_workaround_1-bp-hardening-support.patch queue-4.15/arm-arm64-kvm-turn-kvm_psci_version-into-a-static-inline.patch queue-4.15/arm-arm64-kvm-implement-psci-1.0-support.patch queue-4.15/arm64-kvm-add-smccc_arch_workaround_1-fast-handling.patch queue-4.15/arm64-kvm-report-smccc_arch_workaround_1-bp-hardening-support.patch queue-4.15/arm-arm64-smccc-implement-smccc-v1.1-inline-primitive.patch queue-4.15/arm64-idmap-use-awx-flags-for-.idmap.text-.pushsection-directives.patch queue-4.15/arm64-kvm-make-psci_version-a-fast-path.patch queue-4.15/arm64-cpufeature-__this_cpu_has_cap-shouldn-t-stop-early.patch queue-4.15/arm64-kpti-add-enable-callback-to-remap-swapper-using-ng-mappings.patch queue-4.15/arm-arm64-kvm-consolidate-the-psci-include-files.patch queue-4.15/arm64-add-skeleton-to-harden-the-branch-predictor-against-aliasing-attacks.patch queue-4.15/arm-arm64-kvm-add-smccc-accessors-to-psci-code.patch queue-4.15/arm64-kvm-use-per-cpu-vector-when-bp-hardening-is-enabled.patch queue-4.15/arm64-kvm-increment-pc-after-handling-an-smc-trap.patch