ports/emulators/xen-kernel/files/0004-gnttab-correct-maptrack-table-accesses.patch
Roger Pau Monné 50c059acb6 xen: apply XSA-{217,218,219,220,221,222,224}
Approved by:	bapt
Sponsored by:	Citrix Systems R&D
MFH:		2017Q2
2017-06-20 13:04:23 +00:00

84 lines
2.9 KiB
Diff

From bb765f7863e5d19eebcfb29c117e2909bce241e7 Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Thu, 15 Jun 2017 12:05:29 +0100
Subject: [PATCH 4/4] gnttab: correct maptrack table accesses
In order to observe a consistent (limit,pointer-table) pair, the reader
needs to either hold the maptrack lock (in line with documentation) or
both sides need to order their accesses suitably (the writer side
barrier was removed by commit dff515dfea ["gnttab: use per-VCPU
maptrack free lists"], and a read side barrier has never been there).
Make the writer publish a new table page before limit (for bounds
checks to work), and new list head last (for racing maptrack_entry()
invocations to work). At the same time add read barriers to lockless
readers.
Additionally get_maptrack_handle() must not assume ->maptrack_head to
not change behind its back: Another handle may be put (updating only
->maptrack_tail) and then got or stolen (updating ->maptrack_head).
This is part of XSA-218.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
---
xen/common/grant_table.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index 81a1a8b..c4d73af 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -395,7 +395,7 @@ get_maptrack_handle(
struct grant_table *lgt)
{
struct vcpu *curr = current;
- int i;
+ unsigned int i, head;
grant_handle_t handle;
struct grant_mapping *new_mt;
@@ -451,17 +451,20 @@ get_maptrack_handle(
new_mt[i].ref = handle + i + 1;
new_mt[i].vcpu = curr->vcpu_id;
}
- new_mt[i - 1].ref = curr->maptrack_head;
/* Set tail directly if this is the first page for this VCPU. */
if ( curr->maptrack_tail == MAPTRACK_TAIL )
curr->maptrack_tail = handle + MAPTRACK_PER_PAGE - 1;
- write_atomic(&curr->maptrack_head, handle + 1);
-
lgt->maptrack[nr_maptrack_frames(lgt)] = new_mt;
+ smp_wmb();
lgt->maptrack_limit += MAPTRACK_PER_PAGE;
+ do {
+ new_mt[i - 1].ref = read_atomic(&curr->maptrack_head);
+ head = cmpxchg(&curr->maptrack_head, new_mt[i - 1].ref, handle + 1);
+ } while ( head != new_mt[i - 1].ref );
+
spin_unlock(&lgt->maptrack_lock);
return handle;
@@ -727,6 +730,7 @@ static unsigned int mapkind(
for ( handle = 0; !(kind & MAPKIND_WRITE) &&
handle < lgt->maptrack_limit; handle++ )
{
+ smp_rmb();
map = &maptrack_entry(lgt, handle);
if ( !(map->flags & (GNTMAP_device_map|GNTMAP_host_map)) ||
map->domid != rd->domain_id )
@@ -1094,6 +1098,7 @@ __gnttab_unmap_common(
return;
}
+ smp_rmb();
map = &maptrack_entry(lgt, op->handle);
grant_read_lock(lgt);
--
2.1.4