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Subject[PATCH v2 10/16] arm64: KVM: Report SMCCC_ARCH_WORKAROUND_1 BP hardening support
Date
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.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
include/linux/arm-smccc.h | 5 +++++
virt/kvm/arm/psci.c | 17 +++++++++++++++--
2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index dc68aa5a7261..e1ef944ef1da 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.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>
diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
index a021b62ed762..5677d16abc71 100644
--- a/virt/kvm/arm/psci.c
+++ b/virt/kvm/arm/psci.c
@@ -407,14 +407,27 @@ static int kvm_psci_call(struct kvm_vcpu *vcpu)
int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
{
u32 func_id = smccc_get_function(vcpu);
- u32 val;
+ u32 val, feature;

switch (func_id) {
case ARM_SMCCC_VERSION_FUNC_ID:
val = ARM_SMCCC_VERSION_1_1;
break;
case ARM_SMCCC_ARCH_FEATURES_FUNC_ID:
- val = -1; /* Nothing supported yet */
+ feature = smccc_get_arg1(vcpu);
+ switch(feature) {
+#ifdef CONFIG_ARM64
+ case ARM_SMCCC_ARCH_WORKAROUND_1:
+ if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR))
+ val = 0;
+ else
+ val = -1;
+ break;
+#endif
+ default:
+ val = -1;
+ break;
+ }
break;
default:
return kvm_psci_call(vcpu);
--
2.14.2
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