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Re: [Xen-devel] [PATCH] xen/grant-table: correctly initialize grant table version 1
On 2012-12-20 4:20, Matt Wilson wrote:
Commit 85ff6acb075a484780b3d763fdf41596d8fc0970 (xen/granttable: Grant
tables V2 implementation) changed the GREFS_PER_GRANT_FRAME macro from
a constant to a conditional expression. The expression depends on
grant_table_version being appropriately set. Unfortunately, at init
time grant_table_version will be 0. The GREFS_PER_GRANT_FRAME
conditional expression checks for "grant_table_version == 1", and
therefore returns the number of grant references per frame for v2.
This causes gnttab_init() to allocate fewer pages for gnttab_list, as
a frame can old half the number of v2 entries than v1 entries. After
gnttab_resume() is called, grant_table_version is appropriately
set. nr_init_grefs will then be miscalculated and gnttab_free_count
will hold a value larger than the actual number of free gref entries.
Correct.
If a guest is heavily utilizing improperly initialized v1 grant
tables, memory corruption can occur. One common manifestation is
corruption of the vmalloc list, resulting in a poisoned pointer
derefrence when accessing /proc/meminfo or /proc/vmallocinfo:
[ 40.770064] BUG: unable to handle kernel paging request at 0000200200001407
[ 40.770083] IP: [<ffffffff811a6fb0>] get_vmalloc_info+0x70/0x110
[ 40.770102] PGD 0
[ 40.770107] Oops: 0000 [#1] SMP
[ 40.770114] CPU 10
This patch introduces a static variable, grefs_per_grant_frame, to
cache the calculated value. gnttab_init() now calls
gnttab_request_version() early so that grant_table_version and
grefs_per_grant_frame can be appropriately set. A few BUG_ON()s have
been added to prevent this type of bug from reoccurring in the future.
Thanks for posting this.
This is caused by not initializing grant_table_version in gnttab_init()
before gnttab_resume(). How about only adding gnttab_request_version()
and BUG_ON() to check grant_table_version in gnttab_init(), then no need
to change GREFS_PER_GRANT_FRAME into grefs_per_grant_frame and add more
BUG_ON() to check grefs_per_grant_frame?
For example, in gnttab_init()
....
+gnttab_request_version();
+BUG_ON(grant_table_version == 0);
....
Thanks
Annie
Signed-off-by: Matt Wilson<msw@xxxxxxxxxx>
Reviewed-and-Tested-by: Steven Noonan<snoonan@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk<konrad.wilk@xxxxxxxxxx>
Cc: Annie Li<annie.li@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxx
---
drivers/xen/grant-table.c | 41 +++++++++++++++++++++++------------------
1 files changed, 23 insertions(+), 18 deletions(-)
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 043bf07..011fdc3 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -55,10 +55,6 @@
/* External tools reserve first few grant table entries. */
#define NR_RESERVED_ENTRIES 8
#define GNTTAB_LIST_END 0xffffffff
-#define GREFS_PER_GRANT_FRAME \
-(grant_table_version == 1 ? \
-(PAGE_SIZE / sizeof(struct grant_entry_v1)) : \
-(PAGE_SIZE / sizeof(union grant_entry_v2)))
static grant_ref_t **gnttab_list;
static unsigned int nr_grant_frames;
@@ -153,6 +149,7 @@ static struct gnttab_ops *gnttab_interface;
static grant_status_t *grstatus;
static int grant_table_version;
+static int grefs_per_grant_frame;
static struct gnttab_free_callback *gnttab_free_callback_list;
@@ -766,12 +763,14 @@ 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;
+ BUG_ON(grefs_per_grant_frame == 0);
+
new_nr_grant_frames = nr_grant_frames + more_frames;
- extra_entries = more_frames * GREFS_PER_GRANT_FRAME;
+ extra_entries = more_frames * grefs_per_grant_frame;
- nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) /
RPP;
+ nr_glist_frames = (nr_grant_frames * grefs_per_grant_frame + RPP - 1) /
RPP;
new_nr_glist_frames =
- (new_nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
+ (new_nr_grant_frames * grefs_per_grant_frame + RPP - 1) / RPP;
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])
@@ -779,12 +778,12 @@ static int grow_gnttab_list(unsigned int more_frames)
}
- for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;
- i< GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
+ for (i = grefs_per_grant_frame * nr_grant_frames;
+ i< grefs_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 = grefs_per_grant_frame * nr_grant_frames;
gnttab_free_count += extra_entries;
nr_grant_frames = new_nr_grant_frames;
@@ -904,7 +903,8 @@ EXPORT_SYMBOL_GPL(gnttab_unmap_refs);
static unsigned nr_status_frames(unsigned nr_grant_frames)
{
- return (nr_grant_frames * GREFS_PER_GRANT_FRAME + SPP - 1) / SPP;
+ BUG_ON(grefs_per_grant_frame == 0);
+ return (nr_grant_frames * grefs_per_grant_frame + SPP - 1) / SPP;
}
static int gnttab_map_frames_v1(xen_pfn_t *frames, unsigned int nr_gframes)
@@ -1068,6 +1068,7 @@ static void gnttab_request_version(void)
rc = HYPERVISOR_grant_table_op(GNTTABOP_set_version,&gsv, 1);
if (rc == 0&& gsv.version == 2) {
grant_table_version = 2;
+ grefs_per_grant_frame = PAGE_SIZE / sizeof(union
grant_entry_v2);
gnttab_interface =&gnttab_v2_ops;
} else if (grant_table_version == 2) {
/*
@@ -1080,10 +1081,9 @@ static void gnttab_request_version(void)
panic("we need grant tables version 2, but only version 1 is
available");
} else {
grant_table_version = 1;
+ grefs_per_grant_frame = PAGE_SIZE / sizeof(struct
grant_entry_v1);
gnttab_interface =&gnttab_v1_ops;
}
- printk(KERN_INFO "Grant tables using version %d layout.\n",
- grant_table_version);
}
int gnttab_resume(void)
@@ -1092,6 +1092,8 @@ int gnttab_resume(void)
char *kmsg = "Failed to kmalloc pages for pv in hvm grant frames\n";
gnttab_request_version();
+ printk(KERN_INFO "Grant tables using version %d layout.\n",
+ grant_table_version);
max_nr_gframes = gnttab_max_grant_frames();
if (max_nr_gframes< nr_grant_frames)
return -ENOSYS;
@@ -1137,9 +1139,10 @@ static int gnttab_expand(unsigned int req_entries)
int rc;
unsigned int cur, extra;
+ BUG_ON(grefs_per_grant_frame == 0);
cur = nr_grant_frames;
- extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /
- GREFS_PER_GRANT_FRAME);
+ extra = ((req_entries + (grefs_per_grant_frame-1)) /
+ grefs_per_grant_frame);
if (cur + extra> gnttab_max_grant_frames())
return -ENOSPC;
@@ -1157,21 +1160,23 @@ int gnttab_init(void)
unsigned int nr_init_grefs;
int ret;
+ gnttab_request_version();
nr_grant_frames = 1;
boot_max_nr_grant_frames = __max_nr_grant_frames();
/* Determine the maximum number of frames required for the
* grant reference free list on the current hypervisor.
*/
+ BUG_ON(grefs_per_grant_frame == 0);
max_nr_glist_frames = (boot_max_nr_grant_frames *
- GREFS_PER_GRANT_FRAME / RPP);
+ grefs_per_grant_frame / RPP);
gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
GFP_KERNEL);
if (gnttab_list == NULL)
return -ENOMEM;
- nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) /
RPP;
+ nr_glist_frames = (nr_grant_frames * grefs_per_grant_frame + RPP - 1) /
RPP;
for (i = 0; i< nr_glist_frames; i++) {
gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);
if (gnttab_list[i] == NULL) {
@@ -1185,7 +1190,7 @@ int gnttab_init(void)
goto ini_nomem;
}
- nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;
+ nr_init_grefs = nr_grant_frames * grefs_per_grant_frame;
for (i = NR_RESERVED_ENTRIES; i< nr_init_grefs - 1; i++)
gnttab_entry(i) = i + 1;
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