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Re: [Xen-devel] [PATCH v6 06/11] x86/vmce: emulate MSR_IA32_MCG_EXT_CTL

>>> On 06.07.17 at 04:03, <haozhong.zhang@xxxxxxxxx> wrote:
> How is about generalize above two else cases by
>             else if ( evc->size >= offsetof(typeof(*evc), mcg_cap) +
>                                    sizeof(evc->mcg_cap) )
>             {
>                 struct hvm_vmce_vcpu vmce = { };
>                 memcpy(&vmce, &evc->vmce,
>                        evc->size - offsetof(typeof(*evc), mcg_cap));
>                 ret = vmce_restore_vcpu(v, &vmce);
>             }

Fundamentally yes, but as you say ...

> However, I'm not sure whether it's safe to blindly copy what is passed
> in 'evc->vmce'. Before this patch, the else-if branch only copies
> mcg_cap if the size of evc->vmce is larger than the size of mcg_cap,
> so it implies no?

... I think we ought to at least avoid copying partial fields. Hence
I think the generalization would involve introduction of a table of
sizes / boundaries at which the copied range may end.


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