Re: [PATCH] KVM: nVMX: Clear pending KVM_REQ_GET_VMCS12_PAGES when leaving nested

[Jan Kiszka <jan.kiszka@web.de>]

On 21.07.19 13:57, Liran Alon wrote:
>
>
>> On 21 Jul 2019, at 14:52, Jan Kiszka <jan.kiszka@web.de> wrote:
>>
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> Letting this pend may cause nested_get_vmcs12_pages to run against an
>> invalid state, corrupting the effective vmcs of L1.
>>
>> This was triggerable in QEMU after a guest corruption in L2, followed by
>> a L1 reset.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>
> Good catch.
> Reviewed-by: Liran Alon <liran.alon@oracle.com>
>
> This would have been more easily diagnosed in case free_nested() would NULL cached_vmcs12 and cached_shadow_vmcs12
> after kfree() and add to get_vmcs12() & get_shadow_vmcs12() a relevant BUG_ON() call.

The NULL'ifying makes sense, patch follows. But the helpers are too often called
unconditionally, thus cause false positives when adding the BUG_ON.

Jan

>
> I would submit such a patch separately.
>
> -Liran
>
>> ---
>>
>> And another gremlin. I'm afraid there is at least one more because
>> vmport access from L2 is still failing in QEMU. This is just another
>> fallout from that. At least the host seems stable now.
>>
>> arch/x86/kvm/vmx/nested.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index 0f1378789bd0..4cdab4b4eff1 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -220,6 +220,8 @@ static void free_nested(struct kvm_vcpu *vcpu)
>> 	if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon)
>> 		return;
>>
>> +	kvm_clear_request(KVM_REQ_GET_VMCS12_PAGES, vcpu);
>> +
>> 	vmx->nested.vmxon = false;
>> 	vmx->nested.smm.vmxon = false;
>> 	free_vpid(vmx->nested.vpid02);
>> --
>> 2.16.4