Re: [Xen-devel] [v8][PATCH 12/17] xen/x86/ept: handle reserved device memory in ept_handle_violation

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Dec 01, 2014 at 05:24:30PM +0800, Tiejun Chen wrote:
> We always reserve these ranges since we never allow any stuff to
> poke them.

s/any stuff to poke them/guest to access them./
> 
> But in theory some untrusted VM can maliciously access them. So we
> need to intercept this approach. But we just don't want to leak
> anything or introduce any side affect since other OSs may touch them
> by careless behavior, so its enough to have a lightweight way, and
> it shouldn't be same as those broken pages which cause domain crush.

s/crush/crash/
> 
> So we just need to return with next eip then let VM/OS itself handle

s/So//

s/itself//
> such a scenario as its own logic.

s/as its own/using its own/
> 
> Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
> ---
>  xen/arch/x86/hvm/vmx/vmx.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 2907afa..3ee884a 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -2403,6 +2403,7 @@ static void ept_handle_violation(unsigned long 
> qualification, paddr_t gpa)
>      p2m_type_t p2mt;
>      int ret;
>      struct domain *d = current->domain;
> +    struct p2m_get_reserved_device_memory pgrdm;
>  
>      /*
>       * We treat all write violations also as read violations.
> @@ -2438,6 +2439,23 @@ static void ept_handle_violation(unsigned long 
> qualification, paddr_t gpa)
>          __trace_var(TRC_HVM_NPF, 0, sizeof(_d), &_d);
>      }
>  
> +    /* This means some untrusted VM can maliciously access reserved
> +     * device memory. But we just don't want to leak anything or
> +     * introduce any side affect since other OSs may touch them by
> +     * careless behavior, so its enough to have a lightweight way.
> +     * Here we just need to return with next eip then let VM/OS itself
> +     * handle such a scenario as its own logic.
> +     */
> +    pgrdm.gfn = gfn;
> +    pgrdm.domain = d;
> +    ret = iommu_get_reserved_device_memory(p2m_check_reserved_device_memory,
> +                                           &pgrdm);
> +    if ( ret )
> +    {
> +        update_guest_eip();
> +        return;
> +    }
> +
>      if ( qualification & EPT_GLA_VALID )
>      {
>          __vmread(GUEST_LINEAR_ADDRESS, &gla);
> -- 
> 1.9.1
> 

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