[src/trunk]: src/sys/arch/xen/xen fix intentional, but eventually faulty off-...

[jdolecek <jdolecek%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/fbc444039414
branches:  trunk
changeset: 1022620:fbc444039414
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Wed Jul 28 21:38:50 2021 +0000

description:
fix intentional, but eventually faulty off-by-one for the maximum number
of segments for I/O - this was supposed to allow MAXPHYS-size I/O even
with page offset, but actually ended up letting through I/O up to
MAXPHYS+PAGE_SIZE

the KASSERT(bcount < MAXPHYS) is kept as-is, since at that place the number
of segments should already be validated, so it's kernel bug if the size
is still too big there

fixes PR port-xen/56328 by Greg Oster

diffstat:

 sys/arch/xen/xen/xbdback_xenbus.c |  7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diffs (28 lines):

diff -r 20b9b2375c1a -r fbc444039414 sys/arch/xen/xen/xbdback_xenbus.c
--- a/sys/arch/xen/xen/xbdback_xenbus.c Wed Jul 28 11:32:21 2021 +0000
+++ b/sys/arch/xen/xen/xbdback_xenbus.c Wed Jul 28 21:38:50 2021 +0000
@@ -1,4 +1,4 @@
-/*      $NetBSD: xbdback_xenbus.c,v 1.97 2021/02/21 20:02:25 jdolecek Exp $      */
+/*      $NetBSD: xbdback_xenbus.c,v 1.98 2021/07/28 21:38:50 jdolecek Exp $      */
 
 /*
  * Copyright (c) 2006 Manuel Bouyer.
@@ -26,7 +26,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xbdback_xenbus.c,v 1.97 2021/02/21 20:02:25 jdolecek Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xbdback_xenbus.c,v 1.98 2021/07/28 21:38:50 jdolecek Exp $");
 
 #include <sys/buf.h>
 #include <sys/condvar.h>
@@ -71,8 +71,7 @@
 #define VBD_BSIZE 512
 #define VBD_MAXSECT ((PAGE_SIZE / VBD_BSIZE) - 1)
 
-/* Need to alloc one extra page to account for possible mapping offset */
-#define VBD_VA_SIZE    (MAXPHYS + PAGE_SIZE)
+#define VBD_VA_SIZE                    MAXPHYS
 #define VBD_MAX_INDIRECT_SEGMENTS      VBD_VA_SIZE >> PAGE_SHIFT
 
 CTASSERT(XENSHM_MAX_PAGES_PER_REQUEST >= VBD_MAX_INDIRECT_SEGMENTS);