linux-kernel - Re: [PATCH v10 1/5] KVM: arm64: Add a vcpu flag to control ptrauth for guest

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Date:   Tue, 23 Apr 2019 16:44:19 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Amit Daniel Kachhap <amit.kachhap@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Kristina Martsenko <kristina.martsenko@....com>,
        kvmarm@...ts.cs.columbia.edu,
        Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 1/5] KVM: arm64: Add a vcpu flag to control ptrauth
 for guest

On Tue, Apr 23, 2019 at 10:12:34AM +0530, Amit Daniel Kachhap wrote:
> A per vcpu flag is added to check if pointer authentication is
> enabled for the vcpu or not. This flag may be enabled according to
> the necessary user policies and host capabilities.
> 
> This patch also adds a helper to check the flag.
> 
> Reviewed-by: Dave Martin <Dave.Martin@....com>
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Christoffer Dall <christoffer.dall@....com>
> Cc: kvmarm@...ts.cs.columbia.edu
> ---
> Changes since v9:
> 
> * Added ptrauth cpufeature static check in vcpu_has_ptrauth [Marc Zyngier].
> 
>  arch/arm64/include/asm/kvm_host.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 7a096fd..7ccac42 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -355,10 +355,15 @@ struct kvm_vcpu_arch {
>  #define KVM_ARM64_HOST_SVE_ENABLED	(1 << 4) /* SVE enabled for EL0 */
>  #define KVM_ARM64_GUEST_HAS_SVE		(1 << 5) /* SVE exposed to guest */
>  #define KVM_ARM64_VCPU_SVE_FINALIZED	(1 << 6) /* SVE config completed */
> +#define KVM_ARM64_GUEST_HAS_PTRAUTH	(1 << 7) /* PTRAUTH exposed to guest */
>  
>  #define vcpu_has_sve(vcpu) (system_supports_sve() && \
>  			    ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
>  
> +#define vcpu_has_ptrauth(vcpu)	((system_supports_address_auth() || \
> +				  system_supports_generic_auth()) && \

Come to think of it, should this be
system_supports_address_auth() _&&_ system_supports_generic_auth()?

It won't make a functional difference today though, since today
kvm_vcpu_enable_ptrauth() won't set KVM_ARM64_GUEST_HAS_PTRAUTH without
system_supports_address_auth() and system_supports_generic_auth() both
true.

With || here, we won't have to change this if supporting the two auth
types independently in the future though.

Either way, my Reviewed-by stands.

Cheers
---Dave