Re: [Xen-devel] [PATCH v6 7/8] xen/arm: don't iomem_permit_access for reserved-memory regions

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 16/08/2019 00:36, Stefano Stabellini wrote:
> Don't allow reserved-memory regions to be remapped into any unprivileged
> guests, until reserved-memory regions are properly supported in Xen. For
> now, do not call iomem_permit_access on them, because giving
> iomem_permit_access to dom0 means that the toolstack will be able to
> assign the region to a domU.
>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> ---
>
> Changes in v6:
> - compare against "/reserved-memory/"
>
> Changes in v5:
> - fix check condition
> - use strnicmp
> - return error
> - improve commit message
>
> Changes in v4:
> - compare the parent name with reserved-memory
> - use dt_node_cmp
>
> Changes in v3:
> - new patch
> ---
>   xen/arch/arm/domain_build.c | 24 ++++++++++++++++--------
>   1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 4c8404155a..673ffa453f 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -1155,15 +1155,23 @@ static int __init map_range_to_domain(const struct 
> dt_device_node *dev,
>       bool need_mapping = !dt_device_for_passthrough(dev);
>       int res;
>   
> -    res = iomem_permit_access(d, paddr_to_pfn(addr),
> -                              paddr_to_pfn(PAGE_ALIGN(addr + len - 1)));
> -    if ( res )
> +    /*
> +     * Don't give iomem permissions for reserved-memory ranges to domUs
In upstream Xen, this is only called for Dom0. So what are you referring to?

> +     * until reserved-memory support is complete.
But as I pointed out before reserved-memory support is not going to happen via 
iomem. This is an abuse of the interface.
> +     */
A better comment would be:

"reserved-memory regions are RAM carved out for special purpose. They are not 
MMIO and therefore a domain should not be able to manage them via the IOMEM 
interface".
> +    if ( strnicmp(dt_node_full_name(dev), "/reserved-memory/",
> +         strlen("/reserved-memory/")) != 0 )
>       {
> -        printk(XENLOG_ERR "Unable to permit to dom%d access to"
> -               " 0x%"PRIx64" - 0x%"PRIx64"\n",
> -               d->domain_id,
> -               addr & PAGE_MASK, PAGE_ALIGN(addr + len) - 1);
> -        return res;
> +        res = iomem_permit_access(d, paddr_to_pfn(addr),
> +                paddr_to_pfn(PAGE_ALIGN(addr + len - 1)));
> +        if ( res )
> +        {
> +            printk(XENLOG_ERR "Unable to permit to dom%d access to"
> +                    " 0x%"PRIx64" - 0x%"PRIx64"\n",
> +                    d->domain_id,
> +                    addr & PAGE_MASK, PAGE_ALIGN(addr + len) - 1);
> +            return res;
> +        }
>       }
>   
>       if ( need_mapping )
Cheers,

--
Julien Grall

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