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

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Message-ID: <f9ebe12e-b6df-690b-1279-b7e2709c9e25@arm.com>
Date:   Wed, 24 Apr 2019 11:27:50 +0530
From:   Amit Daniel Kachhap <amit.kachhap@....com>
To:     Dave Martin <Dave.Martin@....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

Hi,

On 4/23/19 9:14 PM, Dave Martin wrote:
> 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()?
I thought about it and kept it this way so that the implementation 
limitation is not introduced in this patch but only in a single place in 
the 3rd patch where all the documentation and reasoning is present on 
doing this way.
> 
> 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.
Yes right.
> 
> Either way, my Reviewed-by stands.
Thanks,
Amit D
> 
> Cheers
> ---Dave
>