From fae7d5be8bb8b7a5b7005c4f3b812a47661a721e Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Tue, 20 Jun 2017 14:29:51 +0200 Subject: [PATCH] x86/mm: disallow page stealing from HVM domains The operation's success can't be controlled by the guest, as the device model may have an active mapping of the page. If we nevertheless permitted this operation, we'd have to add further TLB flushing to prevent scenarios like "Domains A (HVM), B (PV), C (PV); B->target==A Steps: 1. B maps page X from A as writable 2. B unmaps page X without a TLB flush 3. A sends page X to C via GNTTABOP_transfer 4. C maps page X as pagetable (potentially causing a TLB flush in C, but not in B) At this point, X would be mapped as a pagetable in C while being writable through a stale TLB entry in B." A similar scenario could be constructed for A using XENMEM_exchange and some arbitrary PV domain C then having this page allocated. This is XSA-217. Reported-by: Jann Horn Signed-off-by: Jan Beulich Acked-by: George Dunlap Reviewed-by: Konrad Rzeszutek Wilk --- xen/arch/x86/mm.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 101ab33193..5dfb876e54 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -4418,6 +4418,9 @@ int steal_page( bool_t drop_dom_ref = 0; const struct domain *owner = dom_xen; + if ( paging_mode_external(d) ) + return -1; + spin_lock(&d->page_alloc_lock); if ( is_xen_heap_page(page) || ((owner = page_get_owner(page)) != d) ) -- 2.30.2