Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <41b9a6c6-37b0-5d23-ebfb-134af360ebf9@redhat.com>
Date:   Tue, 28 Sep 2021 18:52:47 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.1.0
Subject: Re: [PATCH v2 0/4] KVM: nSVM: avoid TOC/TOU race when checking vmcb12
Content-Language: en-US
To:     Emanuele Giuseppe Esposito <eesposit@redhat.com>,
        kvm@vger.kernel.org
Cc:     Maxim Levitsky <mlevitsk@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org
References: <20210917120329.2013766-1-eesposit@redhat.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <20210917120329.2013766-1-eesposit@redhat.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 17/09/21 14:03, Emanuele Giuseppe Esposito wrote:
> Currently there is a TOC/TOU race between the check of vmcb12's
> efer, cr0 and cr4 registers and the later save of their values in
> svm_set_*, because the guest could modify the values in the meanwhile.
> 
> To solve this issue, this serie introuces and uses svm->nested.save
> structure in enter_svm_guest_mode to save the current value of efer,
> cr0 and cr4 and later use these to set the vcpu->arch.* state.
> 
> Patch 1 just refactor the code to simplify the next two patches,
> patch 2 introduces svm->nested.save to cache the efer, cr0 and cr4 fields
> and in patch 3 and 4 we use it to avoid TOC/TOU races.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>

Most of my remarks from the RFC still apply, so I will wait for v3. 
Thanks, and sorry for the time between send and review.

Paolo