linux-kernel - Re: [RFC PATCH 3/3] nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU races

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Date:   Tue, 14 Sep 2021 10:20:32 +0200
From:   Emanuele Giuseppe Esposito <eesposit@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] nSVM: use svm->nested.save to load vmcb12
 registers and avoid TOC/TOU races



On 12/09/2021 12:42, Maxim Levitsky wrote:
>>   
>> -	if (!nested_vmcb_valid_sregs(vcpu, &vmcb12->save) ||
>> +	if (!nested_vmcb_valid_sregs(vcpu, &svm->nested.save) ||
>>   	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {

> If you use a different struct for the copied fields, then it makes
> sense IMHO to drop the 'control' parameter from nested_vmcb_check_controls,
> and just use the svm->nested.save there directly.
> 

Ok, what you say in patch 2 makes sense to me. I can create a new struct 
vmcb_save_area_cached, but I need to keep nested.ctl because 1) it is 
used also elsewhere, and different fields from the one checked here are 
read/set and 2) using another structure (or the same 
vmcb_save_area_cached) in its place would just duplicate the same fields 
of nested.ctl, creating even more confusion and possible inconsistency.

Let me know if you disagree.

Thank you,
Emanuele