Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on its physical address width.

From: Yu Zhang
Date: Mon Sep 18 2017 - 05:59:15 EST

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
return kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx,


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.


Anyway, this should be a bug and thanks for pointing this out, and
I'll send out the fix later.