linux-kernel - Re: [PATCH 1/6] KVM: nVMX: avoid NULL pointer dereference with incorrect EVMCS GPAs

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Date:   Tue, 10 Mar 2020 02:15:22 +0000
From:   linmiaohe <linmiaohe@...wei.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH 1/6] KVM: nVMX: avoid NULL pointer dereference with
 incorrect EVMCS GPAs

Hi:
Vitaly Kuznetsov <vkuznets@...hat.com> writes:
>When an EVMCS enabled L1 guest on KVM will tries doing enlightened VMEnter with EVMCS GPA = 0 the host crashes because the
>
>evmcs_gpa != vmx->nested.hv_evmcs_vmptr
>
>condition in nested_vmx_handle_enlightened_vmptrld() will evaluate to false (as nested.hv_evmcs_vmptr is zeroed after init). The crash will happen on vmx->nested.hv_evmcs pointer dereference.
>
>Another problematic EVMCS ptr value is '-1' but it only causes host crash after nested_release_evmcs() invocation. The problem is exactly the same as with '0', we mistakenly think that the EVMCS pointer hasn't changed and thus nested.hv_evmcs_vmptr is valid.
>
>Resolve the issue by adding an additional !vmx->nested.hv_evmcs check to nested_vmx_handle_enlightened_vmptrld(), this way we will always be trying kvm_vcpu_map() when nested.hv_evmcs is NULL and this is supposed to catch all invalid EVMCS GPAs.
>
>Also, initialize hv_evmcs_vmptr to '0' in nested_release_evmcs() to be consistent with initialization where we don't currently set hv_evmcs_vmptr to '-1'.
>
>Cc: stable@...r.kernel.org
>Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>---
> arch/x86/kvm/vmx/nested.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)

Good catch! Patch looks good for me. Thanks!
Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>