[PATCH v2] KVM: apic: avoid calculating pending eoi from an uninitialized val

[PATCH v2] KVM: apic: avoid calculating pending eoi from an uninitialized val

[linmiaohe]

From: Miaohe Lin <linmiaohe@huawei.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.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.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;
 }
 
-- 
2.19.1

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

[Vitaly Kuznetsov]

linmiaohe <linmiaohe@huawei.com> writes:

> From: Miaohe Lin <linmiaohe@huawei.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@redhat.com>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.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

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

[linmiaohe]

Vitaly Kuznetsov <vkuznets@redhat.com> writes:
>linmiaohe <linmiaohe@huawei.com> writes:
>
>> From: Miaohe Lin <linmiaohe@huawei.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.

My bad, sorry about it, I should be more careful about it. I will drop the last sentence in v3. Thanks.