From 9808ed0b1ebc3a5d2aa08a9ff91fcf3ecb42bc9f Mon Sep 17 00:00:00 2001 From: George Dunlap Date: Thu, 15 Jun 2017 16:24:02 +0100 Subject: [PATCH 1/4] gnttab: Fix handling of dev_bus_addr during unmap If a grant has been mapped with the GNTTAB_device_map flag, calling grant_unmap_ref() with dev_bus_addr set to zero should cause the GNTTAB_device_map part of the mapping to be left alone. Unfortunately, at the moment, op->dev_bus_addr is implicitly checked before clearing the map and adjusting the pin count, but only the bits above 12; and it is not checked at all before dropping page references. This means a guest can repeatedly make such a call to cause the reference count to drop to zero, causing the page to be freed and re-used, even though it's still mapped in its pagetables. To fix this, always check op->dev_bus_addr explicitly for being non-zero, as well as op->flag & GNTMAP_device_map, before doing operations on the device_map. While we're here, make the logic a bit cleaner: * Always initialize op->frame to zero and set it from act->frame, to reduce the chance of untrusted input being used * Explicitly check the full dev_bus_addr against act->frame << PAGE_SHIFT, rather than ignoring the lower 12 bits This is part of XSA-224. Reported-by: Jan Beulich Signed-off-by: George Dunlap Signed-off-by: Jan Beulich --- xen/common/grant_table.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c index ba10e76..2671761 100644 --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -1085,8 +1085,6 @@ __gnttab_unmap_common( ld = current->domain; lgt = ld->grant_table; - op->frame = (unsigned long)(op->dev_bus_addr >> PAGE_SHIFT); - if ( unlikely(op->handle >= lgt->maptrack_limit) ) { gdprintk(XENLOG_INFO, "Bad handle (%d).\n", op->handle); @@ -1169,16 +1167,14 @@ __gnttab_unmap_common( goto act_release_out; } - if ( op->frame == 0 ) - { - op->frame = act->frame; - } - else + op->frame = act->frame; + + if ( op->dev_bus_addr ) { - if ( unlikely(op->frame != act->frame) ) + if ( unlikely(op->dev_bus_addr != pfn_to_paddr(act->frame)) ) PIN_FAIL(act_release_out, GNTST_general_error, - "Bad frame number doesn't match gntref. (%lx != %lx)\n", - op->frame, act->frame); + "Bus address doesn't match gntref (%"PRIx64" != %"PRIpaddr")\n", + op->dev_bus_addr, pfn_to_paddr(act->frame)); map->flags &= ~GNTMAP_device_map; } @@ -1271,7 +1267,8 @@ __gnttab_unmap_common_complete(struct gnttab_unmap_common *op) else status = &status_entry(rgt, op->ref); - if ( unlikely(op->frame != act->frame) ) + if ( op->dev_bus_addr && + unlikely(op->dev_bus_addr != pfn_to_paddr(act->frame)) ) { /* * Suggests that __gntab_unmap_common failed early and so @@ -1282,7 +1279,7 @@ __gnttab_unmap_common_complete(struct gnttab_unmap_common *op) pg = mfn_to_page(op->frame); - if ( op->flags & GNTMAP_device_map ) + if ( op->dev_bus_addr && (op->flags & GNTMAP_device_map) ) { if ( !is_iomem_page(act->frame) ) { @@ -1353,6 +1350,7 @@ __gnttab_unmap_grant_ref( /* Intialise these in case common contains old state */ common->new_addr = 0; common->rd = NULL; + common->frame = 0; __gnttab_unmap_common(common); op->status = common->status; @@ -1417,6 +1415,7 @@ __gnttab_unmap_and_replace( /* Intialise these in case common contains old state */ common->dev_bus_addr = 0; common->rd = NULL; + common->frame = 0; __gnttab_unmap_common(common); op->status = common->status; -- 2.1.4