On 5/9/20 7:59 AM, Paolo Bonzini wrote:
> On 09/05/20 00:09, Jim Mattson wrote:
>>> + if (static_cpu_has(X86_FEATURE_PKU) &&
>>> + kvm_read_cr4_bits(vcpu, X86_CR4_PKE) &&
>>> + vcpu->arch.pkru != vcpu->arch.host_pkru)
>>> + __write_pkru(vcpu->arch.pkru);
>> This doesn't seem quite right to me. Though rdpkru and wrpkru are
>> contingent upon CR4.PKE, the PKRU resource isn't. It can be read with
>> XSAVE and written with XRSTOR. So, if we don't set the guest PKRU
>> value here, the guest can read the host value, which seems dodgy at
>> best.
>>
>> Perhaps the second conjunct should be: (kvm_read_cr4_bits(vcpu,
>> X86_CR4_PKE) || (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU)).
Thanks Jim.
>
> You're right. The bug was preexistent, but we should fix it in 5.7 and
> stable as well.
Paolo, Do you want me to send this fix separately? Or I will send v3 just
adding this fix. Thanks
>
>>> }
>>> EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
>>>
>>> void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
>>> {
>>> + /*
>>> + * eager fpu is enabled if PKEY is supported and CR4 is switched
>>> + * back on host, so it is safe to read guest PKRU from current
>>> + * XSAVE.
>>> + */
>> I don't understand the relevance of this comment to the code below.
>>
>
> It's probably stale.
Will remove it.
>
> Paolo
>
