linux-kernel - Re: [PATCH v2] KVM: apic: avoid calculating pending eoi from an uninitialized val

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Message-ID: <8736b3rk8j.fsf@vitty.brq.redhat.com>
Date:   Fri, 21 Feb 2020 17:14:04 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        pbonzini@...hat.com, rkrcmar@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com
Subject: Re: [PATCH v2] KVM: apic: avoid calculating pending eoi from an uninitialized val

linmiaohe <linmiaohe@...wei.com> writes:

> From: Miaohe Lin <linmiaohe@...wei.com>
>
> When pv_eoi_get_user() fails, 'val' may remain uninitialized and the return
> value of pv_eoi_get_pending() becomes random. Fix the issue by initializing
> the variable.

Well, now the 'perfect' commit message doesn't match the patch :-). I
think you (or Paolo upon commit) can just drop the last sentence.

>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
> v1->v2:
> Collect Vitaly' R-b.
> Use Vitaly' alternative wording.
> Explicitly handle the error, as suggested by Sean.
> ---
>  arch/x86/kvm/lapic.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 4f14ec7525f6..b4aca77efc8e 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -627,9 +627,11 @@ static inline bool pv_eoi_enabled(struct kvm_vcpu *vcpu)
>  static bool pv_eoi_get_pending(struct kvm_vcpu *vcpu)
>  {
>  	u8 val;
> -	if (pv_eoi_get_user(vcpu, &val) < 0)
> +	if (pv_eoi_get_user(vcpu, &val) < 0) {
>  		printk(KERN_WARNING "Can't read EOI MSR value: 0x%llx\n",
>  			   (unsigned long long)vcpu->arch.pv_eoi.msr_val);
> +		return false;
> +	}
>  	return val & 0x1;
>  }

-- 
Vitaly