linux-kernel - Re: [PATCH 2/2] KVM: x86: fix KVM_SET

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Date:	Thu, 17 Oct 2013 21:04:21 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, gleb@...hat.com, agraf@...e.de,
	chao.zhou@...el.com, magnus@...en.cx, kvm@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: fix KVM_SET_XCRS loop

On Thu, Oct 17, 2013 at 04:50:47PM +0200, Paolo Bonzini wrote:
> The loop was always using 0 as the index.  This means that
> any rubbish after the first element of the array went undetected.
> It seems reasonable to assume that no KVM userspace did that.

It is not a typo, look at __kvm_set_xcr when setting
guest_xcrs->xcrs[i].value, with i != 0.

The code is not prepared to deal with XCR != 0 (because its not
implemented in hw).

> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f4e1391..f91dff2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3062,9 +3062,9 @@ static int kvm_vcpu_ioctl_x86_set_xcrs(struct kvm_vcpu *vcpu,
>  
>  	for (i = 0; i < guest_xcrs->nr_xcrs; i++)
>  		/* Only support XCR0 currently */
> -		if (guest_xcrs->xcrs[0].xcr == XCR_XFEATURE_ENABLED_MASK) {
> +		if (guest_xcrs->xcrs[i].xcr == XCR_XFEATURE_ENABLED_MASK) {
>  			r = __kvm_set_xcr(vcpu, XCR_XFEATURE_ENABLED_MASK,
> -				guest_xcrs->xcrs[0].value);
> +				guest_xcrs->xcrs[i].value);
>  			break;
>  		}
>  	if (r)
> -- 
> 1.8.3.1
--
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