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([2001:b07:6468:f312:8d3e:39e5:cd88:13cc]) by smtp.gmail.com with ESMTPSA id a8sm8171159wrg.85.2020.05.07.06.46.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 May 2020 06:46:10 -0700 (PDT) Subject: Re: [PATCH 1/2] KVM: nSVM: Check that MBZ bits in CR3 and CR4 are not set on vmrun of nested guests To: Krish Sadhukhan , kvm@vger.kernel.org, Wei Huang References: <20200504223523.7166-1-krish.sadhukhan@oracle.com> <20200504223523.7166-2-krish.sadhukhan@oracle.com> From: Paolo Bonzini Message-ID: Date: Thu, 7 May 2020 15:46:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200504223523.7166-2-krish.sadhukhan@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 05/05/20 00:35, Krish Sadhukhan wrote: > + if (!(vmcb->save.efer & EFER_LMA)) { > + if (vmcb->save.cr4 & X86_CR4_PAE) { > + if (vmcb->save.cr3 & MSR_CR3_LEGACY_PAE_RESERVED_MASK) > + return false; > + } else { > + if (vmcb->save.cr3 & MSR_CR3_LEGACY_RESERVED_MASK) > + return false; > + } > + if (vmcb->save.cr4 & MSR_CR4_LEGACY_RESERVED_MASK) > + return false; > + } else { > + if ((vmcb->save.cr4 & X86_CR4_PAE) && > + (vmcb->save.cr3 & MSR_CR3_LONG_RESERVED_MASK)) > + return false; > + if (vmcb->save.cr4 & MSR_CR4_RESERVED_MASK) > + return false; > + } > + > if ((vmcb->control.intercept & (1ULL << INTERCEPT_VMRUN)) == 0) > return false; > I think checking LMA from the guest state is incorrect, the number of bits in CR3 and CR4 remains 64 as long as the host processor is 64-bits. This of course is unless you have reproduced on bare metal that a hypervisor running in 32-bit mode ignores the top 32 bits. Also, the checks for CR4 must use the guest's reserved bits, using kvm_valid_cr4. However this can be a bit slow so it is probably a good idea to cache the bits in kvm_update_cpuid. Thanks, Paolo > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h > index df3474f..796c083 100644 > --- a/arch/x86/kvm/svm/svm.h > +++ b/arch/x86/kvm/svm/svm.h > @@ -354,7 +354,12 @@ static inline bool gif_set(struct vcpu_svm *svm) > } > > /* svm.c */ > -#define MSR_INVALID 0xffffffffU > +#define MSR_CR3_LEGACY_RESERVED_MASK 0xfe7U > +#define MSR_CR3_LEGACY_PAE_RESERVED_MASK 0x7U > +#define MSR_CR3_LONG_RESERVED_MASK 0xfff0000000000fe7U > +#define MSR_CR4_LEGACY_RESERVED_MASK 0xffbaf000U > +#define MSR_CR4_RESERVED_MASK 0xffffffffffbaf000U > +#define MSR_INVALID 0xffffffffU >