Re: [PATCH 3/4] KVM: arm64: Allow PtrAuth to be enabled from userspace on non-VHE systems

Andrew Scull
2020-06-15T09:09:43Z

On Mon, Jun 15, 2020 at 09:19:53AM +0100, Marc Zyngier wrote:
> Now that the scene is set for enabling PtrAuth on non-VHE, drop
> the restrictions preventing userspace from enabling it.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/reset.c | 21 ++++++++++-----------
> 1 file changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index d3b209023727..2a929789fe2e 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -42,6 +42,11 @@ static u32 kvm_ipa_limit;
> #define VCPU_RESET_PSTATE_SVC (PSR_AA32_MODE_SVC | PSR_AA32_A_BIT | \
> PSR_AA32_I_BIT | PSR_AA32_F_BIT)
>
> +static bool system_has_full_ptr_auth(void)
> +{
> + return system_supports_address_auth() && system_supports_generic_auth();
> +}
> +
> /**
> * kvm_arch_vm_ioctl_check_extension
> *
> @@ -80,8 +85,7 @@ int kvm_arch_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> break;
> case KVM_CAP_ARM_PTRAUTH_ADDRESS:
> case KVM_CAP_ARM_PTRAUTH_GENERIC:
> - r = has_vhe() && system_supports_address_auth() &&
> - system_supports_generic_auth();
> + r = system_has_full_ptr_auth();
> break;
> default:
> r = 0;
> @@ -205,19 +209,14 @@ static void kvm_vcpu_reset_sve(struct kvm_vcpu *vcpu)
>
> static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
> {
> - /* Support ptrauth only if the system supports these capabilities. */
> - if (!has_vhe())
> - return -EINVAL;
> -
> - if (!system_supports_address_auth() ||
> - !system_supports_generic_auth())
> - return -EINVAL;
> /*
> * For now make sure that both address/generic pointer authentication
> - * features are requested by the userspace together.
> + * features are requested by the userspace together and the system
> + * supports these capabilities.
> */
> if (!test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
> - !test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features))
> + !test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features) ||
> + !system_has_full_ptr_auth())
> return -EINVAL;
>
> vcpu->arch.flags |= KVM_ARM64_GUEST_HAS_PTRAUTH;

That was easy. Let EL2 use ptrauth and it can save and restore the
guest's state and done.

Acked-by: Andrew Scull <ascull@google.com>