From: Tetsu Yamamoto <tyamamot@redhat.com>
Date: Mon, 7 Apr 2008 17:13:21 -0400
Subject: [xen] memory corruption due to VNIF increase
Message-id: 47FA8E71.3010403@redhat.com
O-Subject: [RHEL5.2][PATCH] xen: Memory corruption due to VNIF increase
Bugzilla: 441390

This patch is for BZ#441390.
https://bugzilla.redhat.com/show_bug.cgi?id=441390

[Description]
The extendable grant table to allow to increase VNIF number per guest
has a problem.  It assumed that one of its data structure, free list,
was the same size as the grant table.  But actually it's only half as
large.  This may cause memory corruption.  This patch fix the free list
allocation.

[Upstream Status]
Already committed:
- fix grant table bug
  http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/4018c0da3360

[brew ID]
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1245014

[Test Status]
Tested on i386, x86_64, and ia64, with kernel -88.
Using netperf (TCP, 16/131072 byte message size), Dom0 and PV guest with
6 VNIFs can communicate simultaneously with no problem.

I have no idea how to test the memory corruption directly, but I believe
the netperf test shows at leaset there is no regression.

Please review and ACK.

Tetsu Yamamoto

# HG changeset patch
# User Keir Fraser <keir.fraser@citrix.com>
# Date 1206957787 -3600
# Node ID 4018c0da336008e5dfb1163bddbdfbc328c8f5c4
# Parent  5486a234923da1fbab13eef6165f25c54ab63bd9
xen: fix grant table bug

A PV OS has two grant table data structures: the grant table itself
and a free list.  The free list is composed of an array of pages,
which grow dynamically as the guest OS requires more grants.  While
the grant table contains 8-byte entries, the free list contains 4-byte
entries.  So we have half as many pages in the free list than in the
grant table.

There was a bug in the free list allocation code. The free list was
indexed as if it was the same size as the grant table.  But it's only
half as large.  So memory got corrupted, and I was seeing crashes in
the slab allocator later on.

Signed-off-by: Michael Abd-El-Malek <mabdelmalek@cmu.edu>

Acked-by: Mark McLoughlin <markmc@redhat.com>
Acked-by: Bill Burns <bburns@redhat.com>
Acked-by: Don Dutile <ddutile@redhat.com>

diff --git a/drivers/xen/core/gnttab.c b/drivers/xen/core/gnttab.c
index fe3228f..e6dd198 100644
--- a/drivers/xen/core/gnttab.c
+++ b/drivers/xen/core/gnttab.c
@@ -46,7 +46,7 @@
 /* External tools reserve first few grant table entries. */
 #define NR_RESERVED_ENTRIES 8
 #define GNTTAB_LIST_END 0xffffffff
-#define GREFS_PER_GRANT_FRAME (PAGE_SIZE / sizeof(grant_entry_t))
+#define ENTRIES_PER_GRANT_FRAME (PAGE_SIZE / sizeof(grant_entry_t))
 
 static grant_ref_t **gnttab_list;
 static unsigned int nr_grant_frames;
@@ -67,6 +67,9 @@ static int gnttab_expand(unsigned int req_entries);
 #define RPP (PAGE_SIZE / sizeof(grant_ref_t))
 #define gnttab_entry(entry) (gnttab_list[(entry) / RPP][(entry) % RPP])
 
+#define nr_freelist_frames(grant_frames)				\
+	(((grant_frames) * ENTRIES_PER_GRANT_FRAME + RPP - 1) / RPP)
+
 static int get_free_entries(int count)
 {
 	unsigned long flags;
@@ -368,24 +371,25 @@ EXPORT_SYMBOL_GPL(gnttab_cancel_free_callback);
 static int grow_gnttab_list(unsigned int more_frames)
 {
 	unsigned int new_nr_grant_frames, extra_entries, i;
+	unsigned int nr_glist_frames, new_nr_glist_frames;
 
 	new_nr_grant_frames = nr_grant_frames + more_frames;
-	extra_entries       = more_frames * GREFS_PER_GRANT_FRAME;
+	extra_entries       = more_frames * ENTRIES_PER_GRANT_FRAME;
 
-	for (i = nr_grant_frames; i < new_nr_grant_frames; i++)
-	{
+	nr_glist_frames = nr_freelist_frames(nr_grant_frames);
+	new_nr_glist_frames = nr_freelist_frames(new_nr_grant_frames);
+	for (i = nr_glist_frames; i < new_nr_glist_frames; i++) {
 		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_ATOMIC);
 		if (!gnttab_list[i])
 			goto grow_nomem;
 	}
 
-
-	for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;
-	     i < GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
+	for (i = ENTRIES_PER_GRANT_FRAME * nr_grant_frames;
+	     i < ENTRIES_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
 		gnttab_entry(i) = i + 1;
 
 	gnttab_entry(i) = gnttab_free_head;
-	gnttab_free_head = GREFS_PER_GRANT_FRAME * nr_grant_frames;
+	gnttab_free_head = ENTRIES_PER_GRANT_FRAME * nr_grant_frames;
 	gnttab_free_count += extra_entries;
 
 	nr_grant_frames = new_nr_grant_frames;
@@ -395,7 +399,7 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 	
 grow_nomem:
-	for ( ; i >= nr_grant_frames; i--)
+	for ( ; i >= nr_glist_frames; i--)
 		free_page((unsigned long) gnttab_list[i]);
 	return -ENOMEM;
 }
@@ -566,8 +570,8 @@ static int gnttab_expand(unsigned int req_entries)
 	unsigned int cur, extra;
 
 	cur = nr_grant_frames;
-	extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /
-		 GREFS_PER_GRANT_FRAME);
+	extra = ((req_entries + (ENTRIES_PER_GRANT_FRAME-1)) /
+		 ENTRIES_PER_GRANT_FRAME);
 	if (cur + extra > max_nr_grant_frames())
 		return -ENOSPC;
 
@@ -580,7 +584,7 @@ static int gnttab_expand(unsigned int req_entries)
 int __init gnttab_init(void)
 {
 	int i;
- 	unsigned int max_nr_glist_frames;
+	unsigned int max_nr_glist_frames, nr_glist_frames;
  	unsigned int nr_init_grefs;
 
 	if (!is_running_on_xen())
@@ -592,16 +596,15 @@ int __init gnttab_init(void)
  	/* Determine the maximum number of frames required for the
  	 * grant reference free list on the current hypervisor.
  	 */
- 	max_nr_glist_frames = (boot_max_nr_grant_frames *
- 			       GREFS_PER_GRANT_FRAME /
- 			       (PAGE_SIZE / sizeof(grant_ref_t)));
+	max_nr_glist_frames = nr_freelist_frames(boot_max_nr_grant_frames);
  
  	gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
  			      GFP_KERNEL);
  	if (gnttab_list == NULL)
  		return -ENOMEM;
  
- 	for (i = 0; i < nr_grant_frames; i++) {
+	nr_glist_frames = nr_freelist_frames(nr_grant_frames);
+	for (i = 0; i < nr_glist_frames; i++) {
  		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);
  		if (gnttab_list[i] == NULL)
  			goto ini_nomem;
@@ -610,7 +613,7 @@ int __init gnttab_init(void)
 	if (gnttab_resume() < 0)
 		return -ENODEV;
 
- 	nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;
+	nr_init_grefs = nr_grant_frames * ENTRIES_PER_GRANT_FRAME;
  
  	for (i = NR_RESERVED_ENTRIES; i < nr_init_grefs - 1; i++)
  		gnttab_entry(i) = i + 1;