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xen/grant-table: correctly initialize grant table version 1
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Commit 85ff6ac (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.

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.

Signed-off-by: Matt Wilson <msw@amazon.com>
Reviewed-and-Tested-by: Steven Noonan <snoonan@amazon.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Annie Li <annie.li@oracle.com>
Cc: xen-devel@lists.xen.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # v3.3 and newer
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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@mswilson @konradwilk
mswilson authored and konradwilk committed Jan 15, 2013
1 parent 6337a23 commit d0b4d64
Showing 1 changed file with 29 additions and 19 deletions.
48 changes: 29 additions & 19 deletions drivers/xen/grant-table.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -56,10 +56,6 @@
/* 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;
Expand Down Expand Up @@ -154,6 +150,7 @@ 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;

Expand Down Expand Up @@ -767,25 +764,27 @@ 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])
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 = 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;
Expand Down Expand Up @@ -957,7 +956,8 @@ 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)
Expand Down Expand Up @@ -1115,6 +1115,7 @@ 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) {
/*
Expand All @@ -1127,17 +1128,17 @@ 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)
static int gnttab_setup(void)
{
unsigned int max_nr_gframes;

gnttab_request_version();
max_nr_gframes = gnttab_max_grant_frames();
if (max_nr_gframes < nr_grant_frames)
return -ENOSYS;
Expand All @@ -1160,6 +1161,12 @@ int gnttab_resume(void)
return 0;
}

int gnttab_resume(void)
{
gnttab_request_version();
return gnttab_setup();
}

int gnttab_suspend(void)
{
gnttab_interface->unmap_frames();
Expand All @@ -1171,9 +1178,10 @@ 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;

Expand All @@ -1191,21 +1199,23 @@ 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) {
Expand All @@ -1214,12 +1224,12 @@ int gnttab_init(void)
}
}

if (gnttab_resume() < 0) {
if (gnttab_setup() < 0) {
ret = -ENODEV;
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;
Expand Down

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