Re: [Xen-devel] [v8][PATCH 13/17] xen/mem_access: don't allow accessing reserved device memory

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.12.14 at 10:24, <tiejun.chen@xxxxxxxxx> wrote:
> --- a/xen/common/mem_access.c
> +++ b/xen/common/mem_access.c
> @@ -55,6 +55,43 @@ void mem_access_resume(struct domain *d)
>      }
>  }
>  
> +/* We can't expose reserved device memory. */
> +static int mem_access_check_rdm(struct domain *d, uint64_aligned_t start,
> +                                uint32_t nr)
> +{
> +    uint32_t i;
> +    struct p2m_get_reserved_device_memory pgrdm;
> +    int rc = 0;
> +
> +    if ( !is_hardware_domain(d) && iommu_use_hap_pt(d) )

Why?

> +    {
> +        for ( i = 0; i < nr; i++ )
> +        {
> +            pgrdm.gfn = start + i;
> +            pgrdm.domain = d;
> +            rc = 
> iommu_get_reserved_device_memory(p2m_check_reserved_device_memory,
> +                                                  &pgrdm);
> +            if ( rc < 0 )
> +            {
> +                printk(XENLOG_WARNING
> +                       "Domain %d can't check reserved device memory.\n",

If I saw this text in a log file, it wouldn't mean anything to me.
Additionally this is only partly useful without also listing the
offending domain (which isn't d afaict) and the GFN.

> +                       d->domain_id);
> +                return rc;
> +            }
> +
> +            if ( rc == 1 )
> +            {
> +                printk(XENLOG_WARNING
> +                       "Domain %d: we shouldn't mem_access reserved device 
> memory.\n",

This one's only marginally better than the one above.

> +                       d->domain_id);
> +                return rc;
> +            }
> +        }
> +    }
> +
> +    return rc;
> +}
> +
>  int mem_access_memop(unsigned long cmd,
>                       XEN_GUEST_HANDLE_PARAM(xen_mem_access_op_t) arg)
>  {
> @@ -99,6 +136,10 @@ int mem_access_memop(unsigned long cmd,
>                ((mao.pfn + mao.nr - 1) > domain_get_maximum_gpfn(d))) )
>              break;
>  
> +        rc =  mem_access_check_rdm(d, mao.pfn, mao.nr);
> +        if ( rc == 1 )
> +            break;

So you decided to return 1 from the hypercall - what is that
supposed to mean to an unaware caller?

Jan


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