linux-kernel - Re: [PATCH] KVM/nVMX: Do not validate that posted_intr_desc

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Date:   Wed, 24 Oct 2018 04:01:09 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH] KVM/nVMX: Do not validate that posted_intr_desc_addr is
 page aligned

On Sat, Oct 20, 2018 at 11:42:59PM +0200, KarimAllah Ahmed wrote:
> The spec only requires the posted interrupt descriptor address to be
> 64-bytes aligned (i.e. bits[0:5] == 0). Using page_address_valid also
> forces the address to be page aligned.
> 
> Only validate that the address does not cross the maximum physical address
> without enforcing a page alignment.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Fixes: 6de84e581c0 ("nVMX x86: check posted-interrupt descriptor addresss on vmentry of L2")
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
>  arch/x86/kvm/vmx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 30bf860..47962f2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11668,7 +11668,7 @@ static int nested_vmx_check_apicv_controls(struct kvm_vcpu *vcpu,
>  	    !nested_exit_intr_ack_set(vcpu) ||
>  	    (vmcs12->posted_intr_nv & 0xff00) ||
>  	    (vmcs12->posted_intr_desc_addr & 0x3f) ||
> -	    (!page_address_valid(vcpu, vmcs12->posted_intr_desc_addr))))
> +	    (vmcs12->posted_intr_desc_addr >> cpuid_maxphyaddr(vcpu)))
>  		return -EINVAL;

Can you update the comment for this code block?  It has a stale blurb
about "the descriptor address has been already checked in
nested_get_vmcs12_pages" and it'd be nice to state why bits[5:0] must
be zero (your changelog is much more helpful than the current comment).

With that:

Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>

>  
>  	/* tpr shadow is needed by all apicv features. */
> -- 
> 2.7.4
>