Re: [PATCH 1/4] xen: Introduce non-broken hypercalls for the paging mempool size

[Anthony PERARD <anthony.perard@citrix.com>]

On Thu, Nov 17, 2022 at 01:08:01AM +0000, Andrew Cooper wrote:
> The existing XEN_DOMCTL_SHADOW_OP_{GET,SET}_ALLOCATION have problems:
> 
>  * All set_allocation() flavours have an overflow-before-widen bug when
>    calculating "sc->mb << (20 - PAGE_SHIFT)".
>  * All flavours have a granularity of 1M.  This was tolerable when the size of
>    the pool could only be set at the same granularity, but is broken now that
>    ARM has a 16-page stopgap allocation in use.
>  * All get_allocation() flavours round up, and in particular turn 0 into 1,
>    meaning the get op returns junk before a successful set op.
>  * The x86 flavours reject the hypercalls before the VM has vCPUs allocated,
>    despite the pool size being a domain property.
>  * Even the hypercall names are long-obsolete.
> 
> Implement a better interface, which can be first used to unit test the
> behaviour, and subsequently correct a broken implementation.  The old
> interface will be retired in due course.
> 
> The unit of bytes (as opposed pages) is a deliberate API/ABI improvement to
> more easily support multiple page granularities.
> 
> This is part of XSA-409 / CVE-2022-33747.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Release-acked-by: Henry Wang <Henry.Wang@arm.com>

Acked-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks,

-- 
Anthony PERARD