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

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Date:   Thu, 20 Feb 2020 17:33:17 +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] KVM: apic: avoid calculating pending eoi from an uninitialized val

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

> From: Miaohe Lin <linmiaohe@...wei.com>
>
> When get user eoi value failed, var val would be uninitialized and result
> in calculating pending eoi from an uninitialized val. Initialize var val
> to 0 to fix this case.

Let me try to suggest an alternative wording,

"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."

>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  arch/x86/kvm/lapic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 4f14ec7525f6..7e77e94f3176 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -626,7 +626,7 @@ static inline bool pv_eoi_enabled(struct kvm_vcpu *vcpu)
>  
>  static bool pv_eoi_get_pending(struct kvm_vcpu *vcpu)
>  {
> -	u8 val;
> +	u8 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);

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

But why compilers don't complain?

-- 
Vitaly