linux-kernel - Re: [PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with SVE

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Date:   Wed, 17 Jun 2020 11:47:41 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Steven Price <steven.price@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with
 SVE

Hi Steven,

On 2020-06-17 11:43, Steven Price wrote:
> If SVE is enabled then 'ret' can be assigned the return value of
> kvm_vcpu_enable_sve() which may be 0 causing future "goto out" sites to
> erroneously return 0 on failure rather than -EINVAL as expected.
> 
> Remove the initialisation of 'ret' and make setting the return value
> explicit to avoid this situation in the future.
> 
> Fixes: 9a3cdf26e336 ("KVM: arm64/sve: Allow userspace to enable SVE for 
> vcpus")
> Reported-by: James Morse <james.morse@....com>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
> The problematic chunk isn't visible in the diff, so reproduced here:
> 
> 	if (!kvm_arm_vcpu_sve_finalized(vcpu)) {
> 		if (test_bit(KVM_ARM_VCPU_SVE, vcpu->arch.features)) {
> 			ret = kvm_vcpu_enable_sve(vcpu);
> 			if (ret)
> 				goto out;
> 		}
> 	} else {
> 		kvm_vcpu_reset_sve(vcpu);
> 	}
> 
>  arch/arm64/kvm/reset.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index d3b209023727..f1057603b756 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -245,7 +245,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu 
> *vcpu)
>   */
>  int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>  {
> -	int ret = -EINVAL;
> +	int ret;
>  	bool loaded;
>  	u32 pstate;
> 
> @@ -269,15 +269,19 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> 
>  	if (test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
>  	    test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features)) {
> -		if (kvm_vcpu_enable_ptrauth(vcpu))
> +		if (kvm_vcpu_enable_ptrauth(vcpu)) {
> +			ret = -EINVAL;
>  			goto out;
> +		}
>  	}
> 
>  	switch (vcpu->arch.target) {
>  	default:
>  		if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
> -			if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
> +			if (cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {

Do you really mean this? Seems counter-productive... :-(

> +				ret = -EINVAL;
>  				goto out;
> +			}
>  			pstate = VCPU_RESET_PSTATE_SVC;
>  		} else {
>  			pstate = VCPU_RESET_PSTATE_EL1;

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...