Hi Andre,
On 4/15/19 4:03 PM, Steven Price wrote:
> On 15/04/2019 12:15, Andre Przywara wrote:
>> 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
>
> I find the naming here a little confusing - it's not really clear what
> "mitigated" means (see below).
>
>> +
>> +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");
>
> Here "mitigated" means "not affected".
>
>> -
>> - if (__hardenbp_enab)
>> + case ARM64_BP_HARDEN_NEEDED:
>> return sprintf(buf, "Mitigation: Branch predictor hardening\n");
>
> And "harden needed" means mitigated.
>
>> -
>> - 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;
>
> Would KVM_BP_HARDEN_NOT_REQUIRED be a more logical name?
I tend to agree with Steven's comment
But then why not also choosing the same terminology for the uapi:
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_UNAFFECTED?
For the same case we seem to have 3 different terminologies. But maybe I
miss something.
In the uapi doc, in case the workaround is not needed do we actually
care to mention the wa is supported?
Thanks
Eric
>
> Steve
>
>> + break;
>> + }
>> break;
>> case ARM_SMCCC_ARCH_WORKAROUND_2:
>> switch (kvm_arm_have_ssbd()) {
>>
>
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