path: root/include
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authorDavid Vrabel <david.vrabel@citrix.com>2015-10-30 14:58:08 +0000
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2015-12-18 10:00:17 -0500
commit454d5d882c7e412b840e3c99010fe81a9862f6fb (patch)
treed5365a0ffb5807285da7af3834b6a73c8531d9bd /include
parent20f36e0380a7e871a711d5e4e59d04d4948326b4 (diff)
Using RING_GET_REQUEST() on a shared ring is easy to use incorrectly (i.e., by not considering that the other end may alter the data in the shared ring while it is being inspected). Safe usage of a request generally requires taking a local copy. Provide a RING_COPY_REQUEST() macro to use instead of RING_GET_REQUEST() and an open-coded memcpy(). This takes care of ensuring that the copy is done correctly regardless of any possible compiler optimizations. Use a volatile source to prevent the compiler from reordering or omitting the copy. This is part of XSA155. CC: stable@vger.kernel.org Signed-off-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Diffstat (limited to 'include')
1 files changed, 14 insertions, 0 deletions
diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
index 7d28aff605c7..7dc685b4057d 100644
--- a/include/xen/interface/io/ring.h
+++ b/include/xen/interface/io/ring.h
@@ -181,6 +181,20 @@ struct __name##_back_ring { \
#define RING_GET_REQUEST(_r, _idx) \
(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
+ * Get a local copy of a request.
+ *
+ * Use this in preference to RING_GET_REQUEST() so all processing is
+ * done on a local copy that cannot be modified by the other end.
+ *
+ * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
+ * to be ineffective where _req is a struct which consists of only bitfields.
+ */
+#define RING_COPY_REQUEST(_r, _idx, _req) do { \
+ /* Use volatile to force the copy into _req. */ \
+ *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \
+} while (0)
#define RING_GET_RESPONSE(_r, _idx) \
(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))