Recent commits added the explicit notion of "Not affected" 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@xxxxxxx>
---
arch/arm/include/asm/kvm_host.h | 12 +++++++++---
arch/arm64/include/asm/cpufeature.h | 6 ++++++
arch/arm64/include/asm/kvm_host.h | 16 ++++++++++++++--
arch/arm64/kernel/cpu_errata.c | 23 ++++++++++++++++++-----
virt/kvm/arm/psci.c | 10 +++++++++-
5 files changed, 56 insertions(+), 11 deletions(-)
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 770d73257ad9..836479e4b340 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -364,7 +364,11 @@ static inline void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) {}
static inline void kvm_arm_vhe_guest_enter(void) {}
static inline void kvm_arm_vhe_guest_exit(void) {}
-static inline bool kvm_arm_harden_branch_predictor(void)
+#define KVM_BP_HARDEN_UNKNOWN -1
+#define KVM_BP_HARDEN_NEEDED 0
+#define KVM_BP_HARDEN_MITIGATED 1
+
+static inline int kvm_arm_harden_branch_predictor(void)
{
switch(read_cpuid_part()) {
#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
@@ -372,10 +376,12 @@ static inline bool kvm_arm_harden_branch_predictor(void)
case ARM_CPU_PART_CORTEX_A12:
case ARM_CPU_PART_CORTEX_A15:
case ARM_CPU_PART_CORTEX_A17:
- return true;
+ return KVM_BP_HARDEN_NEEDED;
#endif
+ case ARM_CPU_PART_CORTEX_A7:
+ return KVM_BP_HARDEN_MITIGATED;
default:
- return false;
+ return KVM_BP_HARDEN_UNKNOWN;
}
}
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 6ccdc97e5d6a..3c5b25c1bda1 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -622,6 +622,12 @@ static inline bool system_uses_irq_prio_masking(void)
cpus_have_const_cap(ARM64_HAS_IRQ_PRIO_MASKING);
}
+#define ARM64_BP_HARDEN_UNKNOWN -1
+#define ARM64_BP_HARDEN_NEEDED 0
+#define ARM64_BP_HARDEN_MITIGATED 1
+
+int get_spectre_v2_workaround_state(void);
+
#define ARM64_SSBD_UNKNOWN -1
#define ARM64_SSBD_FORCE_DISABLE 0
#define ARM64_SSBD_KERNEL 1
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index a01fe087e022..bf9a59b7d1ce 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -555,9 +555,21 @@ static inline void kvm_arm_vhe_guest_exit(void)
isb();
}
-static inline bool kvm_arm_harden_branch_predictor(void)
+#define KVM_BP_HARDEN_UNKNOWN -1
+#define KVM_BP_HARDEN_NEEDED 0
+#define KVM_BP_HARDEN_MITIGATED 1
+
+static inline int kvm_arm_harden_branch_predictor(void)
{
- return cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR);
+ switch (get_spectre_v2_workaround_state()) {
+ case ARM64_BP_HARDEN_NEEDED:
+ return KVM_BP_HARDEN_NEEDED;
+ case ARM64_BP_HARDEN_MITIGATED:
+ return KVM_BP_HARDEN_MITIGATED;
+ case ARM64_BP_HARDEN_UNKNOWN:
+ default:
+ return KVM_BP_HARDEN_UNKNOWN;
+ }
}
#define KVM_SSBD_UNKNOWN -1
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index a1f3188c7be0..7fa23ab09d4e 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -555,6 +555,17 @@ 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_MITIGATED;
+
+ if (!__hardenbp_enab)
+ return ARM64_BP_HARDEN_UNKNOWN;
+
+ return ARM64_BP_HARDEN_NEEDED;
+}
+
/*
* List of CPUs that do not need any Spectre-v2 mitigation at all.
*/
@@ -834,13 +845,15 @@ 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_MITIGATED:
return sprintf(buf, "Not affected\n");
-
- if (__hardenbp_enab)
+ case ARM64_BP_HARDEN_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,
diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
index 34d08ee63747..1da53e0e38f7 100644
--- a/virt/kvm/arm/psci.c
+++ b/virt/kvm/arm/psci.c
@@ -412,8 +412,16 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
feature = smccc_get_arg1(vcpu);
switch(feature) {
case ARM_SMCCC_ARCH_WORKAROUND_1:
- if (kvm_arm_harden_branch_predictor())
+ switch (kvm_arm_harden_branch_predictor()) {
+ case KVM_BP_HARDEN_UNKNOWN:
+ break;
+ case KVM_BP_HARDEN_NEEDED:
val = SMCCC_RET_SUCCESS;
+ break;
+ case KVM_BP_HARDEN_MITIGATED:
+ val = SMCCC_RET_NOT_REQUIRED;
+ break;
+ }
break;
case ARM_SMCCC_ARCH_WORKAROUND_2:
switch (kvm_arm_have_ssbd()) {
--
2.17.1
