Re: [PATCH v3 16/30] KVM: x86 emulator: If LOCK prefix is used dest arg should be memory.

[Andre Przywara <andre.przywara@amd.com>]

Gleb Natapov wrote:
> If LOCK prefix is used dest arg should be memory, otherwise instruction
> should generate #UD.
Well, there is one exception:
There is an AMD specific "lock mov cr0 = mov cr8" equivalence, where 
there is no memory involved (and we intercept this). I am not sure if 
anyone actually uses this code sequence, but it is definitely legal.

Regards,
Andre.

> 
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> ---
>  arch/x86/kvm/emulate.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index b89a8f2..46a7ee3 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -1842,7 +1842,7 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
>  	}
>  
>  	/* LOCK prefix is allowed only with some instructions */
> -	if (c->lock_prefix && !(c->d & Lock)) {
> +	if (c->lock_prefix && (!(c->d & Lock) || c->dst.type != OP_MEM)) {
>  		kvm_queue_exception(ctxt->vcpu, UD_VECTOR);
>  		goto done;
>  	}


-- 
Andre Przywara
AMD-OSRC (Dresden)
Tel: x29712