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([2001:b07:6468:f312:a0c0:5d2e:1d35:17bb]) by smtp.gmail.com with ESMTPSA id a1sm7316698wmj.29.2020.06.04.06.20.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Jun 2020 06:20:54 -0700 (PDT) Subject: Re: WARNING in kvm_inject_emulated_page_fault To: Vitaly Kuznetsov , kvm@vger.kernel.org, sean.j.christopherson@intel.com Cc: syzbot , bp@alien8.de, hpa@zytor.com, jmattson@google.com, joro@8bytes.org, linux-kernel@vger.kernel.org, mingo@redhat.com, syzkaller-bugs@googlegroups.com, tglx@linutronix.de, wanpengli@tencent.com, x86@kernel.org References: <000000000000c8a76e05a73e3be3@google.com> <874krrf6ga.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Message-ID: Date: Thu, 4 Jun 2020 15:20:53 +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: <874krrf6ga.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/06/20 12:53, Vitaly Kuznetsov wrote: > Exception we're trying to inject comes from > > nested_vmx_get_vmptr() > kvm_read_guest_virt() > kvm_read_guest_virt_helper() > vcpu->arch.walk_mmu->gva_to_gpa() > > but it seems it is only set if GVA to GPA convertion fails. In case it > doesn't, we can still fail kvm_vcpu_read_guest_page() and return > X86EMUL_IO_NEEDED but nested_vmx_get_vmptr() doesn't case what we return > and does kvm_inject_emulated_page_fault(). This can happen when VMXON > parameter is MMIO, for example. > > How do fix this? We can either properly exit to userspace for handling > or, if we decide that handling such requests makes little sense, just > inject #GP if exception is not set, e.g. > > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > index 9c74a732b08d..a21e2f32f59b 100644 > --- a/arch/x86/kvm/vmx/nested.c > +++ b/arch/x86/kvm/vmx/nested.c > @@ -4635,7 +4635,11 @@ static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer) > return 1; > > if (kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e)) { > - kvm_inject_emulated_page_fault(vcpu, &e); > + if (e.vector == PF_VECTOR) > + kvm_inject_emulated_page_fault(vcpu, &e); > + else > + kvm_inject_gp(vcpu, 0); > + > return 1; > } > Yes, this is a plausible fix (with a comment explaining that we are taking a shortcut). Perhaps a better check would be r = kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e); if (r != X86EMUL_CONTINUE) { if (r == X86EMUL_PROPAGATE_FAULT) { kvm_inject_emulated_page_fault(vcpu, &e); } else { /* ... */ kvm_inject_gp(vcpu, 0); } return 1; } Are you going to send a patch? Paolo