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

From: Andrew Scull <ascull@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kernel-team@android.com
Subject: Re: [PATCH 3/4] KVM: arm64: Allow PtrAuth to be enabled from userspace on non-VHE systems
Date: Mon, 15 Jun 2020 10:09:35 +0100	[thread overview]
Message-ID: <20200615090935.GF177680@google.com> (raw)
In-Reply-To: <20200615081954.6233-4-maz@kernel.org>

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>