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SubjectRe: [PATCH] KVM: X86: Fix SMRAM accessing even if VM is shutdown
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On 07/02/2018 07:25, Wanpeng Li wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 786cd00..445e702 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7458,6 +7458,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> goto out;
> }
>
> + if (unlikely(vcpu->run->exit_reason == KVM_EXIT_SHUTDOWN)) {
> + r = -EINVAL;
> + goto out;
> + }
> +
> if (vcpu->run->kvm_dirty_regs) {
> r = sync_regs(vcpu);
> if (r != 0)
>

This most likely breaks triple faults in the usual case where they
should result in resetting the system; the KVM API doesn't say that you
should clear vcpu->run->exit_reason before entering.

What exactly causes the EPT misconfig to reach the WARN? That is, how
does kvm_mmu_page_fault end up returning a negative errno value? If I
read the code correctly only tdp_page_fault can do so, so my guess would
be kvm_handle_bad_page:

if (pfn == KVM_PFN_ERR_RO_FAULT)
return RET_PF_EMULATE;

if (pfn == KVM_PFN_ERR_HWPOISON) {
kvm_send_hwpoison_signal(kvm_vcpu_gfn_to_hva(vcpu, gfn),
current);
return RET_PF_RETRY;
}

/* KVM_PFN_ERR_FAULT */
return -EFAULT;

Maybe it should return RET_PF_EMULATE, which would cause an emulation
failure and then an exit with KVM_EXIT_INTERNAL_ERROR.

Thanks,

Paolo

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