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Date: Mon, 18 Sep 2017 17:35:19 +0800 From: Yu Zhang <yu.c.zhang@...ux.intel.com> To: Paolo Bonzini <pbonzini@...hat.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 9/18/2017 4:41 PM, Paolo Bonzini wrote: > 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. Oh, right. It normally goes to handle_cr(). Thanks, Paolo. Yu > >> 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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