Re: [Xen-devel] [PATCH v3] x86: allow 64-bit PV guest kernels to suppress user mode exposure of M2P

[Tim Deegan <tim@xxxxxxx>]

Hi,

At 15:31 +0100 on 24 Apr (1429889471), Jan Beulich wrote:
> --- a/xen/arch/x86/mm/shadow/multi.c
> +++ b/xen/arch/x86/mm/shadow/multi.c
> @@ -1435,6 +1435,14 @@ void sh_install_xen_entries_in_l4(struct
>          shadow_l4e_from_mfn(page_to_mfn(d->arch.perdomain_l3_pg),
>                              __PAGE_HYPERVISOR);
>  
> +    if ( !shadow_mode_refcounts(d) && !is_pv_32on64_domain(d) &&

I think the right check here is !shadow_mode_external(d), i.e. that
this l4e is a mapping of the M2P and not some guest-controlled mapping.

> +         !VM_ASSIST(d, m2p_strict) )
> +    {
> +        /* zap_ro_mpt(mfn_x(sl4mfn)); */
> +        sl4e[shadow_l4_table_offset(RO_MPT_VIRT_START)] = shadow_l4e_empty();
> +        zap_ro_mpt(mfn_x(gl4mfn));

Here and below -- shouldn't the existing PV paths be taking care of
zapping/filling the guest pagetable before we get here?  It doesn't
seem right for shadow pagetable code to be making this kind of change
- especially in a mapping that's not actually "shadowed" per se.

Cheers,

Tim.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel