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SubjectRe: [PATCH v2 10/16] arm64: KVM: Report SMCCC_ARCH_WORKAROUND_1 BP hardening support
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On 29/01/18 17:45, Marc Zyngier wrote:
> 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 */

Conceptually, might it still make sense to initialise val to
NOT_SUPPORTED here, then overwrite it if and when a feature actually is
present? It would in this case save a few lines as well, but I know
multiple assignment can be one of those religious issues, so I'm not too
fussed either way.

Robin.

> + 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);
>

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