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Date: Mon, 18 Sep 2017 10:41:21 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Yu Zhang <yu.c.zhang@...ux.intel.com>, Jim Mattson <jmattson@...gle.com> Cc: kvm list <kvm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Radim Krčmář <rkrcmar@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, xiaoguangrong@...cent.com, Joerg Roedel <joro@...tes.org> Subject: Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on its physical address width. On 18/09/2017 10:15, Yu Zhang wrote: >> >> static bool emulator_get_cpuid(struct x86_emulate_ctxt *ctxt, >> u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, bool >> check_limit) >> { >> return kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx, >> check_limit); >> } >> >> And: >> >> bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, >> u32 *ecx, u32 *edx, bool check_limit) >> { >> u32 function = *eax, index = *ecx; >> struct kvm_cpuid_entry2 *best; >> bool entry_found = true; >> ... >> >> Doesn't this immediately try to dereference a NULL pointer? How much >> testing have you done of this code? > > Thanks Jim. > I have tested this code in a simulator to successfully boot a VM in > shadow mode. Seems this code is not covered(but I am now still > perplexed why this is not covered). Any possibility that the > check_cr_write() is not triggered when emulating the cr operations? CR moves usually don't go through the emulator (the main exception is emulation of invalid guest state when the processor doesn't support unrestricted_guest=1, but even that is unlikely to happen with EFER.LMA=1). This explains why you didn't see the failure. > Anyway, this should be a bug and thanks for pointing this out, and > I'll send out the fix later. Thanks, Paolo
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