Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation

[Wanpeng Li]

Ping, :)
2017-07-11 15:13 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y
> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries
> to emulate invalid guest state task-switch:
>
> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
> kvm_emulate_insn: 42000:0:0f 0b (0x2)
> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
> kvm_inj_exception: #UD (0x0)
> kvm_entry: vcpu 0
> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
> kvm_emulate_insn: 42000:0:0f 0b (0x2)
> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
> kvm_inj_exception: #UD (0x0)
> ......................
>
> It appears that the task-switch emulation updates rflags (and vm86
> flag) only after the segments are loaded, causing vmx->emulation_required
> to be set, when in fact invalid guest state emulation is not needed.
>
> This patch fixes it by updating vmx->emulation_required after the
> rflags (and vm86 flag) is updated in task-switch emulation.
>
> Suggested-by: Nadav Amit <nadav.amit@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
>  arch/x86/kvm/vmx.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f50cbfd..70270a2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu)
>          * TODO: What about debug traps on tss switch?
>          *       Are we supposed to inject them and update dr6?
>          */
> +       vmx->emulation_required = emulation_required(vcpu);
>
>         return 1;
>  }
> --
> 2.7.4
>