58 lines
2.0 KiB
Diff
58 lines
2.0 KiB
Diff
|
From 4e2bc423e0cef0a42f93d989c0980301df1bd462 Mon Sep 17 00:00:00 2001
|
||
|
|
From: David Vrabel <david.vrabel@citrix.com>
|
||
|
|
Date: Fri, 30 Oct 2015 14:58:08 +0000
|
||
|
|
Subject: [PATCH 1/7] xen: Add RING_COPY_REQUEST()
|
||
|
|
|
||
|
|
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>
|
||
|
|
---
|
||
|
|
v2: Update about GCC and bitfields.
|
||
|
|
---
|
||
|
|
include/xen/interface/io/ring.h | 14 ++++++++++++++
|
||
|
|
1 file changed, 14 insertions(+)
|
||
|
|
|
||
|
|
diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
|
||
|
|
index 7d28aff..7dc685b 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))
|
||
|
|
|
||
|
|
--
|
||
|
|
2.1.0
|
||
|
|
|